C A R S O L O G I C A Carsologica 15 Urednik zbirke / Series Editor Franci Gabrovšek MitjaPrelovšek THE DYNAMICS OF THE PRESENT-DAY SPELEOGENETIC PROCESSES IN THE STREAM CAVES OF SLOVENIA Recenzenta / Reviewed by Franci Gabrovšek and Andrej Kranjc Jezikovni pregled / Language review Amidas d.o.o. Oblikovanje in prelom / Design and typesetting Mitja Prelovšek Naslovna fotografija/Cover photo Alojz Troha, DLKJ Izdajatelj / Issued by Inštitut za raziskovanje krasa ZRC SAZU, Postojna / Karst Research Institute ZRC SAZU, Postojna Zanj / Represented by Tadej Slabe Založnik / Published by Založba ZRC / ZRC Publishing, Ljubljana Za založnika / For the publisher Oto Luthar Glavni urednik / Editor-in-Chief Aleš Pogačnik Tisk / Printed by Collegium Graphicum d.o.o. Naklada / Printrun 300 Izdajo knjige je podrpla Javna agencija za knjigo Republike Slovenije. The publication was subsidised by the Slovene Book Agency. CIP - Kataložni zapis o publikaciji Narodna in univerzitetna knjižnica, Ljubljana 551.44(497.4) PRELOVŠEK, Mitja, 1980- The dynamics of the present-day speleogenetic processes in the stream caves of Slovenia / Mitja Prelovšek. - Ljubljana : Založba ZRC = ZRC Publishing, 2012. - (Carsologica, ISSN 1854-2964 ; 15) ISBN 978-961-254-405-8 264383232 © 2012, Založba ZRC, ZRC SAZU. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or trans-mitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Mitja Prelovšek The Dynamics of The PresenT-Day sPeLeogeneTic Processes in The sTream caves of sLovenia Postojna – Ljubljana 2012 conTenTs 1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1 FOREwORD � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 7 1.2 THEORETICAL BACKGROUND � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 8 1.3 FOCUS OF RESEARCH, POSED PROBLEMS, APPROACH � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �11 2 RESEARCH METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.1 MICROMETER MEASUREMENTS � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 15 2.2 MEASUREMENTS wITH LIMESTONE TABLETS� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �16 2�2�1 Preparation of limestone tablets� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �17 2�2�2 Test study � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �18 2�2�3 Measurement errors and correction factors � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 20 2�2�4 Absolute precision of measurements with limestone tablets – comparison with micrometer measurements � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 26 2.3 HYDROCHEMICAL METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.4 OTHER COMPLEMENTARY METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3 CASE STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.1 KRIžNA JAMA-KRIžNA JAMA 2 CAVE SYSTEM � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 33 3�1�1 Measurement location KJ-1 – temporal variability of processes at Brzice� � � � � � � � � � � � � � � � � � � � � � � 39 3�1�2 Measurement location KJ-2 – temporal and spatial variability of processes in the first lake � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 45 3�1�3 Comparison of measurement locations KJ-1 and KJ-2 – differences in sinter deposition rates between rapids and lakes � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 47 3�1�4 Measurement locations KJ-3, KJ-4, and KJ-5 – spatial variability of processes in the water course between Kalvarija and Ponor � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 49 3�1�5 Measurement locations KJ-5, KJ-6, and KJ-7 – mixing of streams from Pisani Rov and from the Blata passage at Kalvarija� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 55 3�1�6 Measurement locations KJ-8, KJ-9, and KJ-10 – speleogenetic processes in Pisani Rov � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 58 3�1�7 Measurement locations KJ-11, KJ-12, KJ-13, and KJ-14 – the influence of tributaries in the Blata passage � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �61 3�1�8 Measurement locations KJ-3 and KJ2-2 (KJ-2-1) – temporal variation of processes in the entrance part of Križna Jama 2 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 64 3�1�9 Measurement locations KJ2-3, KJ2-4, KJ2-5, and KJ2-6 – spatial variability of processes along the main water course in Križna Jama 2� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 67 3�1�10 Conclusion � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 72 3.2 LEKINKA CAVE� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 75 3�2�1 Measurement location L-1 – temporal variability of dissolution rates 75 m from the ponor � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 80 3�2�2 Measurement location L-1 – vertical variability of dissolution rates � � � � � � � � � � � � � � � � � � � � � � � � � � � 86 3�2�3 Measurement locations L-2, L-1, L-3, L-4, L-5, and L-6 – longitudinal variability of dissolution in the entrance part of Lekinka (along a 250 m long watercourse) � � � � � � � � � � � � � � � � 90 3�2�4 Measurement locations L-2, L-1, L-3, L-5, L-6, L-7, L-8, L-9, and L-10 – longitudinal variability of dissolution rates all along the underground water course in Lekinka (from the entrance to the sump) � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 94 3�2�5 Conclusion � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 97 3.3 ŠKOCJANSKE JAME� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 99 3�3�1 Measurement place S-1 and S-2 – temporal variability of processes at Swidovo Razgledišče� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 103 3�3�2 Measurement places S-3, S-4, S-5 and S-6, S-7, S-8, and S-9 – vertical variability of processes at Swidovo Razgledišče and at Martelovo Jezero � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 106 3�3�3 Measurement places S-6, S-3, S-10, S-11, and S-12 – longitudinal variability of processes between flysch-limestone contact and Martelovo Jezero � � � � � � � � � � � � � � � � � � � � � � � � � � � �110 3�3�4 Conclusion � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �112 3.4 POSTOJNA BASIN-PLANINA POLJE CAVE SYSTEM� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �113 3�4�1 Measurement location P-1 – temporal and vertical variability of processes in the entrance area of Postojna cave system � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �118 3�4�2 Measurement locations P-1, P-2, P-3, P-4, P-5, P-6, P-7, and P-8 – temporal and longitudinal variability of processes along underground water flow from Postojna basin to Planina polje� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 122 3�4�3 Measurement locations P-7, P-8, and C-7 – measurement of mixing corrosion at underground confluence of Pivka River and Rak River � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 124 3�4�4 Conclusion � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 126 4 GENERAL CONCLUSIONS, DISCUSSION AND POTENTIAL FOR FURTHER RESEARCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 4.1 METHODOLOGY � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 127 4.2 RATES OF DISSOLUTION/SINTER DEPOSITION� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 128 4.3 RELATION BETwEEN PRESENT-DAY PROCESSES, FACTORS AND FEATURES� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �131 5 POVZETEK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 5.1 UVOD � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 133 5.2 RAZISKOVALNE METODE � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 134 5.3 IZBRANI PRIMERI S SLOVENSKEGA KRASA� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 136 5.4 SPLOŠNI ZAKLJUčKI, DISKUSIJAIN MOžNOST NADALJNJIH RAZISKAV� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �141 6 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 iNTR 1 OduCTiON 1.1 FOREwORD Nearly all current general knowledge related about greatly improved understanding of the to the development of caves in limestone areas chemical equilibrium and chemical kinetics of harkens back to the 19th century, some even to carbonate rock dissolution (White 2000)� The the 18th� At the beginning of the 20th century, the quantification of speleogenetic phenomena principal role of dissolution due to CO2 from the made possible computer modelling of karst soil, nearly all important chemical reactions that aquifer development, which is currently making take place on karst surfaces and underground, great progress� The next step is the successful principles of underground water flow and verti- integration of modelling and field observation, cal hydrological zonation of karst massifs were which has already been done in some studies all familiar� Several researchers defended their to an extent (Palmer 2007, Covington et al� in “universal” ideas with limited field observa- press)� tions but there were also some (e�g� E�A� Martel The knowledge of the underground karst in 1896) that were already aware that “no theory is deepening but some ideas that have already about the origin of caves is universal” and “all of become generally accepted beliefs still require them are partly correct” (Lowe 2000; 30)� comprehensive confirmation� One such generally Many karstological studies during the accepted belief is dissolutional origin and the 20th century brought shifts in emphases from development of caves, which seems to be an on-general theories (e�g� water table controls) to going process in all karst areas� But to be sure investigations of individual underlying processes about that and to obtain more reliable insight and mechanisms of cave development (White into the dissolutional speleogenesis in stream 2000) that deepened the understanding of the caves, comprehensive field measurements are geomorphic evolution of karst surfaces and necessary� To begin this task, the methodology caves, hydrogeological functioning of karst for dissolution rate measurements requires aquifers, and chemical and physical processes substantial improvement and testing in different that take place in the karst� General human karst environments� This has been done in development also helped fulfil the desire for this study and the experiences are presented intensive investigation in many karst regions in Chapter 2� On the basis of field data and and made possible deeper, longer, more efficient experiences, detailed investigation was possible and scientifically supported cave exploration, in the largest and the most interesting cave especially due to the invention of the single rope systems (Chapter 3)� We asked ourselves how technique in the second half of the 20th century� high dissolution rates are, how variable in space The second half of the 20th century also brought and time, where the highest and the lowest rates 7 Introduction are, and what causes them� A temporally and can be sure that they are correct since they are spatially dense net of measurement locations quantitatively based and therefore objective� Our made possible field observation of dissolutional research was carried out in known Slovenian phenomena and a reliable synthesis of results for Classic Karst that developed mainly on limestone each cave system� As a result, though several cave and dolomite under the influence of relatively systems were chosen and limited information shallow - rarely as much as hundreds of meters about dissolution rates were illuminated, we deep - circulation of meteoric water� 1.2 THEORETICAL BACKGROUND Comprehensively speaking, cave systems are in comparison with abrasion when channels formed through the action of speleogenetic agents are big enough for the transport of sediments, which, given various factors and through various dissolution can be recognized easily from processes produce speleogenetic features within a dissolution load in spring waters� it is clear that speleogenetic environment� dissolution takes place in karst massifs, but The main speleogenetic agent in the karst the portion of dissolution involved in channel is water, which transfers dissolved or partly enlargement is usually unknown and therefore weathered rock through karst massifs and also must still be estimated� Generally speaking, the tears away weakly attached rocks/crystals� Water amount of carbonate dissolved in a solution at in a karst system is also a medium that transfers equilibrium depends on the concentration of dissolved or partly weathered rock through a hydrogen ions� The latter is usually defined by speleogenetic environment� Accordingly, water CO2 concentration in the air, with which the erodes, transport and accumulates material water is in contact� When all available CO2 is in/through caves as a part of a water and rock used for dissolution, water becomes saturated� cycle (Natek 1987; 75)� universal physical and The kinetics of the process is at least as chemical laws, particular to the speleogenetic important as the equilibrium� The highest rates environment, define how much rock can be are achieved when a concentration of individual eroded/dissolved, transported or deposited� ions is far from equilibrium (e�g� when water is At a particular location, physicochemical highly undersaturated or supersaturated with properties of water (e�g� CO2 concentration, Ca2+ respect to Ca2+; Ford & Williams 2007; 65)� The concentration, temperature, viscosity, density) highest rate of dissolution or sinter deposition is and some other conditions (e�g� velocity of controlled by a rate-limiting process which can be flow, hydraulic head, structure, texture of rock, (a) a reaction on a crystal surface, (b) conversion erosion base) are crucial factors in regard to the of CO - 2 to H+ and HCO3 (or vice versa) in the water geomorphic action of water� or (c) the transport of ions by diffusion in the Speleogenetic processes are sequences of diffusion boundary layer (dreybrodt & Eisenlohr changes that occur through the actions of agents 2000)� The rate of reaction can be lower due to in a speleogenetic environment and may result impurities in the minerals which inhibit the in specific cave feature formation� it is generally surface reaction (dreybrodt & Eisenlohr 2000)� accepted that the dissolution of carbonate rocks Some substances in the water (e�g� lead, copper, is the most necessary and important process manganese, phosphates, sulphates, sodium for cave formation and development� Although chloride) affect equilibrium concentrations and/ we can debate the importance of dissolution or the kinetics of reaction (Jennings 1985; 23)� 8 Introduction Therefore, the amount and rate of dissolution and the biological (e�g� density of organisms is controlled by many speleogenetic factors� The and their metabolic processes)� Some factors influence of some of them have been studied increase the solubility of carbonates or increase theoretically and experimentally (dreybrodt dissolution rates (e�g� small grains of calcite-1988, dreybrodt 2004), but the variety and micrites, low water Ca2+ concentration, high temporal variability of factors in the natural water CO2 concentration, high flow velocity, environment is usually too great to calculate mixing of saturated waters with different and predict actual rates of processes� Therefore, CO2 concentrations, transition from laminar to several field techniques exist to measure turbulent flow, presence of other acids (sulphuric dissolution rates in caves� acid, nitric acid) and some diluted salts (sodium Although dissolution is (almost) inevitable chloride); some decrease the solubility of for karst and cave formation, the variety and carbonates or decrease dissolution rates or lead rates of other speleogenetic processes can be even toward calcite precipitation (e�g� large quite high, even in karst areas, especially if we crystals-sparites, high water Ca2+ concentration, are dealing with caves close to contact with high degree of poorly soluble rock impurities, non-karstifiable rock (corrasion, sedimentation presence of dolomite, small or decreasing of allochthonous material) or close to cave CO2 concentration in the water, presence of metal entrances in occasionally colder climates ions (lead, zinc, copper, manganese), presence (mechanical breakdown)� The latter is a logical of common ions with CaCO3 or CaMg(CO3)2, consequence of mechanical disequilibrium in presence of bases) and others have bidirectional a karst massif, which is established after the influence (e�g� temperature of water, organic caves are formed (Jennings 1985; 28)� Biological acids, microorganisms, phosphates, presence of weathering can, especially in a warm (20-25 °C) magnesium) (Sweeting 1972, Jennings 1985; 22, and humid climate, play an important role in dreybrodt 1988, dreybrodt 2000; dreybrodt & speleogenesis (Jennings 1985, 32)� Bacterial films Eisenlohr 2000, Ford & Williams 2007, Srdoč exist practically all over the cave’s wall and can et al� 1985)� be responsible for dissolution or deposition� All Speleogenetic features/forms are geomorphic these processes can be complementary to or features that developed under the action of spe-contrary to dissolution� The extent of the final leogenetic processes within cave systems� They form (cave system or individual micro-feature) can be a result of a single process or a combi-depends on the rate of processes and available nation of processes (polygenetic features)� Since time� The latter is highly variable� the early and main topic of geomorphology (and Speleogenetic processes are dependent upon speleology) was dedicated mainly to forms and speleogenetic factors that define how intensively their (sometimes very subjectively determined) an agent will influence the karst massif and geneses (Gams 1962; 3, Natek, 1987), descriptive what kind of influences can be expected� They literature on features is far more common in spe-are numerous and various and range from the leology in comparison with that which discusses geological (e�g� degree of fracturization, chemical speleogenetic processes or factors� composition of rocks, texture and structure of Features that can be found in caves are rock), to the hydrological (e�g� CO2 concentration, numerous by type, genesis and individual Ca2+ concentration, temperature, flow morphology� A comprehensive study of cave velocity, sediment load, presence of other rock features is presented by Slabe (1995)� ions), the meteorological (e�g� external and Nevertheless, the genesis of even some basic cave temperatures, CO2 concentration in and well-studied features (e�g� scallops) is still the air, degree and direction of ventilation) not fully explained� The genesis of scallops is 9 Introduction generally attributed to dissolution (Curl 1966 According to Swinnerton (1932 after Gabrovšek & 1974 after Slabe 1995; 19, Goodchild & Ford 2005) and Rhoades & Sinacori (1941 after Lowe 1971 after Slabe 1995; 20, Lauritzen et al� 1983, 2000), the majority of underground water moves Lauritzen & Lundberg 2000, Ford & Williams along the water table at the top of the phreatic 2007; 256-259), while some authors attribute at zone due to its having the most direct connec-least the initiation to corrasion (Renault 1968; tion between sinks and springs and also due to 563 after Slabe 1995; 20, Häuselmann 2002; 8), high secondary (or tertiary, according to Ford & since they can be found on the surface of almost Williams 2007; 104) porosity� The latter is a result insoluble rocks (e�g� granite)� of long-term evolution, in which the epiphreatic Speleogenetic environments are three- zone seems to be particularly effective for cave dimensional spaces where speleogenesis takes formation (Sweeting 1950 after Jennings 1985; place� usually, they are divided into several 148, Palmer 1984 after Jennings 1985; 148, White zones regarding the prevailing medium that 1988; 269-271 after Gams 2003; 46)� According fills the voids in the karst massif (air or water; to Ford & Ewers (1978) and Ford & Williams permanently, occasionally)� Two main zones are (2007; 129-130), the degree of secondary (or ter-usually put forward (vadose and phreatic)� in the tiary) porosity in the epiphreatic zone strongly vadose, water percolates downwards planarly depends on fracture density – the higher it is, and usually make contact with soil CO2� Since the shallower is a water flow through the phre-such water is highly undersaturated, the majority atic zone (such (sub)horizontal flow can also of dissolution takes place within this zone take place in the epiphreatic zone)� Nevertheless, (Smith & Mead 1962 after Jennings 1985; 156, some researchers (e�g� Jeannin et al� 2000; 345-Gams 1966b, Williams 1963 & 1968 after Ford 346, Häuselmann et al� 2003) agree to the special & Williams 2007; 94, Sweeting 1966 after Ford suitability of the epiphreatic zone for the forma- & Williams 2007; 94)� Contact with air is absent tion of (sub)horizontal flow but do not agree that in phreatic zone, where the water moves due to a there is a relation between the (sub)horizontal hydraulic head in a full pipe flow� The portion of caves in epiphreatic zone to high fracture den-overall dissolution in a phreatic zone is estimated sity (and the four state model described in Ford usually at 5-20 %, in rare cases up to 40 % (Ford & Ewers (1978), since some areas (Siebenhengste- & Williams 2007; 94)� Nevertheless, dissolution Hohgant-Lake of Thun) also exhibit the forma-in the phreatic zone takes place at relatively small tion of passages around 200 m below the water reaction surfaces; therefore, dissolution rates can level, although the rock is densely fractured� be relatively high (Gunn 1986; 382)� dissolution The temporal and spatial variations of karst in the phreatic zone also has significant processes and factors are very common� From geomorphological and hydrological importance, the viewpoint of dissolution, large differences since it makes possible the drainage of extensive in dissolution rates are observed within even non-karst regions� one flood pulse� Nevertheless, speleogenetic Because of high secondary porosity and fluc- processes are so slow that such short time scale tuation of water levels between vadose and phre- variations are often neglected� usually from atic zone, the epiphreatic zone is often enlight- several 10,000s to millions of years are needed ened� This zone (also referred to as the epiphreas, for the formation of a substantial cave system� floodwater zone, temporarily flooded zone) can The dating of cave sediments confirms the very be defined with the highest and the lowest pi- old age of several systems (see Zupan Hajna et ezometric water level in a karst massif (Gams al� 2008 for details)� during such a long period, 2003; 46) or the zone that is regularly flooded speleogenetic factors particularly and related (Häuselmann 2002; 8, Häuselmann et al� 2003)� processes can change significantly� Change of 10 Introduction climate is the most obvious factor, although be understood as just a moment during the long-some significant changes in the catchment term evolution of a cave system, while it remains area, the tectonic position of the karst massif important for the understanding of present-and the position of inflow/outflow are possible� day relations in different climatic-geomorphic Therefore present-day speleogenetic activity can settings� 1.3 FOCUS OF RESEARCH, POSED PROBLEMS, APPROACH The title of this book frames the subject of this are two approaches to this: empirical (from large work in time, theme and space: to small scales; knowledge comes from field • temporal framework (actual, present-day observations) and analytical (from small to large activity and its short-term (daily, monthly, scales; knowledge of basic principles of physics yearly) variation), and chemistry results in an understanding • thematic framework (speleogenetic processes of complex cave system networks; Gabrovšek and their relations to factors and features) and 2005)� The analytical approach was substantially • spatial framework (stream caves usually in deepened in recent decades by physicists and the epiphreatic zone)� chemists while empirical studies of processes are rare even today� in contradistinction to the numerous studies in the past, present-day processes and factors on fossil speleogenesis we decided to focus on were, in the field, mostly defined by the study present-day geomorphic activity� The latter has of cave morphology on the basis of known re-mostly been disregarded in the past due to a pre- lationships between morphology, processes and vailing interest in long-term geomorphic evolu- factors� This provides us the opportunity to in-tion� But we should always be aware that evolu- terpret relevant processes and factors from mor-tionary studies are based on the interpretation of phology� Such an approach (Lauritzen et al� 2000, recent morphology and present-day connections Fig� 1�1a) was and remains common in geomor-between features, factors and relevant processes� phology and speleology� it is very effective and Therefore, the study of present-day phenomena justifiable in an environment where the relations will provide us good insight into the connec- are clear, sometimes even visible, and processes tion between processes, factors and forms and act relatively rapidly� in caves, processes are usu-should reflect all the complexity of geomorphic ally slow, and, since the rock is transformed into activities as well as provide missing quantitative solution, also invisible but observable� Changes data on dissolution and sinter deposition rates in in the hydrological role of underground passages stream caves� are also common (Gospodarič 1976, Šušteršič The second reason for studying present-day et al� 2002)� Additionally, the connection of speleogenetic processes is the limited knowledge karst processes and climatic conditions (trough regarding their rates and variation in known CO2 concentration, temperature and amount of cave systems� Gabrovšek (2005) states that for precipitation) makes the relationship even more the understanding of karst and its evolution one complicated� But can we really relate present-day has to study and understand the basic processes morphology with present-day processes in caves behind it� The process of dissolution is the core with a long evolutionary history? What if present-of the geomorphic activity of the karst and day morphology is inherited from the past; e�g�, knowledge about it is necessary� Basically, there the pre-Holocene period? We can at least suspect 11 Introduction Figure 1.1. Approach to “speleogenetic analysis” suggested by Lauritzen et al. (2000; A) and approach used in this book (B) to interpret speleogenetic relations between present-day processes, potential morphology, present-day factors/agents and their relations to present-day morphology. that due to morphologically, hydro(geo)logically, features� At this point a major deficiency becomes climatologically (and anthopogenically) induced apparent, as we have almost no data (especially) changes of factors that define processes, present- about present-day processes (and factors)� it is day morphology does not necessarily correspond hard to believe that from the middle of the 19th to present-day processes� century, when dissolution was recognized as Since the connection between present-day fea- the main process in cave formation, until now, tures/factors and features seems to be question- we still lack direct measurements of dissolution able or at least for the most part unconfirmed, a rates in caves� This deficiency is characteristic on different approach for interpretation is suggested a world scale (Gunn 1986)� (Fig� 1�1b)� The advantage of such an approach Since the already measured (e�g� Smith et is the separation of the study of morphology al� 1995, Gams 1996, Mihevc 2011; 64, High and processes (with factors), which seems to be & Hanna 1970 after White 2000; 151) and problematic in the study of temporally limited estimated dissolution rates from measurements phenomena� Rates of present-day processes can of factor/agents (Palmer 2007) are usually low also provide us with rough estimations of time in karst streams, we had to test and improve needed for feature formation if actual processes the methodology in order to begin our work� (with factors) are harmonized with the develop- The micro-erosion meter (MEM) seems to ment of actual features and factors not signifi- be inappropriate for expected annual µm cantly changed in the time required for feature differences and for short-term (weekly, monthly) formation� usually the age of features has been measurements, since large errors are expected calculated from dated cave deposits that overlay at places with very low rates (Spate et al� 1985)� or are in any other known temporal relation with Therefore we substantially improved the features (Bosak 2002; 201), which is the only way methodology for dissolution and sinter deposition to define the age of features if no connection is rate measurements using limestone tablets� The found between actual morphology and actual use of limestone tablets for cave measurements processes� as described in Chapter 2�2 plays a crucial role The measurement of processes and relevant in the determination of low dissolution rates factors provide us data for the definition of over relatively very short periods� The simplicity potential morphology in cave passages� Potential of the developed methodology makes possible morphology can then be compared to actual measurements at numerous locations and ones and this offers us the opportunity to consequently spatial and temporal comparison see discrepancies and the extent of inherited of results and enhanced reliability of conclusions� 12 Introduction Stream caves in epiphreatic zone represent accessible part of a karst aquifer� Where it one of the most attractive parts of karst aquifers� was possible, we took into account the cave They often conduct the greatest portion of system instead of one stream cave because the underground water flow and are from both the whole system yields more information about hydrological and geomorphological perspective the integrity of the speleogenetic environment very important� They also represent the easiest (Häuselmann 2002)� 13 RESEAR 2 CH METHOdS Research methods used in this study were measurements� using a micrometer, the accura- mainly devoted to the measurement of processes� cy amounts to the usual 10 µm to up to 0�01 µm Present-day dissolution or sinter deposition rates per measurement (Trudgill 1977; 253), but the can generally be measured using the following amount of error, which is at low rates and at high methodology: frequency measurements relatively higher, repre- • micrometer (MEM; High & Hanna 1970 after sents a serious problem (Spate et al� 1985)� Hy-White 2000, Spate et al� 1985, Mihevc 1993, drochemical measurements offer us much better Mihevc 1997, Mihevc 2001), insight into the short-term temporal variations • limestone tablets (Gams 1959, delannoy 1982 of dissolution and are extensively used over vast after Gams 1985, Gams 1986, Gams 1996, karst areas to calculate chemical denudation rates Newson 1971 after Gunn 1986; 383, Trudgill (see Komac 2005; 129-134 for details)� But from 1975 after Gunn 1986; 383, Sweeting 1979; 64- such results we cannot obtain the rate of passage 65), and enlargement since we lack many variables (i�e� • hydrochemical method (solute load and dis- reaction surface, rate of process in different parts charge; Pulina & Sauro 1993, Ford & Williams of an aquifer)� These problems can be avoided if 2007)� we are measuring the same parameters (solute load and discharge) between two measurement Measurements with MEM and with limestone points at which distance and reaction surface is tablets are highly site-specific and are highlight- known� The condition for such measurements is ed in this study� MEM has been used frequently that the processes are faster than the accuracy on bare surface rock, while limestone tablets of the method, that we have significant length have usually been used for dissolution rate meas- of passage and that hydrochemical changes are urements in soils, much more seldom in caves� not a consequence of any tributary� This is rather The intensity of dissolution in the whole aquifer hard to obtain� was usually calculated using hydrochemical data The best opportunity to obtain the results we and discharge from karst springs� are seeking, which has rarely been used in the The biggest challenge of measurements in the past, is the calculation of dissolution or sinter karst is the low intensity of karst processes, deposition rate from weight loss of limestone while the processes involved in non-karstic areas tablets� Weight loss is relatively easy to measure are usually much more intensive� in most cases with accuracy up to 0�001 mg and since we are measurements in the karst should last several dealing with a quite high reaction surface, very years to be sure that results are truly representa- precise data can be obtained� This finding led us tive� Therefore, in the short term the disadvan- to improve the methodology of using limestone tage is uncertainty of accuracy and reliability of tablets for measurements in caves and to use it as 14 a basis for dissolution and speleothem deposition into the temporal variability of processes and rates from 2005 onwards� can acquire some crucial information regarding Six years of measurements is very little time factors which control the rates of processes� in comparison with the lengthy speleogenesis Another problem is spatial extrapolation� To of some caves (the active ponor cave Markov what extent can we interpolate and extrapolate Spodmol currently contains between 0�78 and rates of processes in space? The available MEM 3�58 Ma old sediments, but the cave is even older; and limestone tablet results from high alpine Zupan Hajna et al� 2008; 247)� Therefore, results karst (Kunaver 1978) and also lowland areas of short-term measurements can be presented (White 2000) show that variability or rates only as mm/a, while other, higher units (mm/ even within medium-sized features (i�e� doline, ka, mm/Ma) are not acceptable or are even slope) can vary considerably� A similar level of extremely hazardous (Gunn 1986, Trudgill variation in the soil was recognized by Trudgil 1986; 499, Trudgill 1994; 113, White 2000)� in et al� (1994, Crabtree & Trudgil 1985), who higher units (mm/ka or mm/Ma), only data exposed 240 limestone tablets transversally to a obtained from long-term average rates should slope at different depths� Similarly to temporal be reported� Generally speaking, the longer the extrapolation, spatial extrapolation depends measurements are taken, the longer the results on the variability of factors which control the can be extrapolated� Nevertheless, we can expect rates of processes� Nevertheless, the variability some time limitations of such measurements of factors along underground water flows in since factors can change significantly with stream caves seems to be lower� Therefore changes in the influence of the environment spatial variability should not be as high as in (i�e� changes of tectonic settings, changes in the soil, epikarst or vadose zone� in spite of drainage basin, climate change, land cover…)� this, several measurements should be made Accidentally or not, Kunaver (1978) recognized to confirm this statement, especially at places that measurements with a MEM (from -20 to where factors can change significantly (i�e� at -100 µm/a) obtained in one year on the surface of changes from free surface flow to pipe flow and the Kanin plateau fit very well with the average vice versa, at confluences due to averaging and dissolution rates (from -15 to -80 µm/a), which mixing corrosion, at changes of water velocity, were defined from pedestals formed after glacial turbulence, etc�)� Measurements at several places retreat at the end of the Pleistocene� Much better and measurements of reliable factors provide results can be obtained if the rates are measured important insight at least into the magnitudes of frequently – from such results we have insight spatial variability of processes� 2.1 MICROMETER MEASUREMENTS The micrometer, generally known also as the several researchers, including as the traversing micro-erosion meter (MEM), since we are micro-erosion meter (T-MEM; Furlani et al� usually measuring erosion (however not always), 2009)� during our measurements, we used a was quite extensively used in the evaluation of MEM from the Karst Research institute ZRC chemical denudation rates on bare karst rock� it SAZu, which had already been used by Mihevc was developed as early as the 1960s (Spate et al� (1993, 1997, 2001) in some caves and on the 1985), first used by High and Hanna (1970 after surface� it consists of a micrometer gauge Ford & Williams 2007) and later improved by connected to an equilateral triangular iron plate 15 Research Methods with 3 triangularly arranged legs at the corners, ber of measurements and the care while taking which lock precisely into stainless steel studs set measurements� Higher temperature differences into the rock surface� The micrometer gauge is (between individual measurements on one side placed several millimetres from the centre of and rock and instrument on another) and probe the iron plate, which enables us to make three erosion represent the most serious errors, which different measurements at each measurement may amount to even more than 20 µm per read-location� The resolution is about 10 µm� Accuracy ing (Spate et al� 1985)� Of yet more concern is the depends also on (Spate et al� 1985): fact that the error of measurements often exceeds • errors due to temperature changes of the the dissolution rates that were measured with a MEM, micrometer� in Yarrangobilly cave (Australia), • errors due to temperature changes of the studs where erosion rates are from 0 to -137 µm/a (with and the rock, median value -8 µm/a!), the error was estimated • errors due to probe erosion� to be between ±8 and ±22 µm (Spate et al� 1985)� Therefore, annual MEM measurements are not The exact value or error depends on tempera- reliable in stream caves that exhibit very low ero-ture changes, material from which the microm- sion/dissolution rates or where the errors (i�e� eter is formed, the softness of the rock, the num- due to temperature changes) can be high� 2.2 MEASUREMENTS wITH LIMESTONE TABLETS The first observations of dissolution using lime- Manojlović 1989, Jennings 1977 after Gavrilović stone tablets (also known as limestone plates, & Manojlović 1989, Trudgill 1977) and later limestone discs, rock tablets, micro-weighed tab- (day 1984 after Gavrilović & Manojlović 1989, lets or weight-loss tablets) were made by Cheva- Gavrilović 1986 after Gavrilović & Manojlović lier (1953 after Gams, 1959) and later by Gams 1989, Sbai 1993, Trudgill et al� 1994, urushibara- (1959)� in the 1960s, an extensive plan for disso- Yoshino 1999 after Ford & Williams 2007, Plan lution measurements in the caves of Slovenia was 2005)� Very rarely limestone tablets were used proposed by društvo za raziskovanje jam Lju- in caves (Chevalier 1953 after Gams 1985, Gams bljana (Society for Cave Exploration Ljubljana), 1959, Rebek 1964, delannoy 1982 after Gams most probably under the influence of Gams� This 1985, Gams 1996), probably because of the dif-plan was never realized� Although the first meas- ficulty of fixing them� urements were made in stream caves, later meas- The methodology of limestone tablets is based urements with limestone tablets were dedicated on weight-loss during exposure� if we know the to dissolution measurements in soil� The greatest reaction surface (the area of the limestone tablet) expansion of the use of such measurements oc- we can transform weight-loss into metric units curred between 1978 and 1983, when extensive (i�e� µm/a)� This simple calculation shows that measurements were carried out all around the we can measure dissolution or sinter deposition world under the leadership of the Commission on rates very precisely in comparison with the Karst denudation at uiS (Gams 1985)� Limestone micrometer if we are using analytical balance� tablets were used in many local studies mostly This led us to start with short-term measurements to evaluate dissolution rates at the point of soil- of dissolution and flowstone deposition rates in rock contact (Trudgill 1975 after Gavrilović & the Slovene underground karst� 16 Research Methods 2.2.1 Preparation of limestone tablets Limestone tablets used by Gams (1985) and in m ∆ this study were made of borehole cores from D = (Equation 2.1), the Lipica limestone quarry� The limestone is of ρ × A× t Senonian (upper Cretaceous) age� it contains 97�7-98�7 % of CaCO3, 0�21 % of MgO, less than where D is a dissolution or sinter deposition 0�1 % of SiO2, 0�05 % of Al2O3 and 0�05 % of S, rate, Δm change in weight of the limestone tablet, 0�007 % of Fe2O3, (GAMS 1985; 365)� According ρ is the density of limestone, A the exposed surface to Folk’s classification, Lipica’s limestone is and t the time of exposure. micrite to biopelmicrite� According to Gams (1985; 365), the density of the limestone is The diameter of the limestone tablet was 2,710 kg/m3, while our measurements, based on always 41 mm, while the thickness ranged from the weight and volume of 235 limestone tablets, 2�6 to 3�5 mm by Gams (1979; 73) and from 5 to showed a slightly lower value (2,688 kg/m3)� The 8 mm in our measurements� Before weighing, latter value was used for transformation of units Gams (1985) dried limestone tablets in an oven at from grams to millimetres with Eq� 2�1� about 110 °C and then cooled them in silica gel� Figure 2.1. Procedure from preparation to final weight calculation of limestone tablets and their treatment after exposure. 17 Research Methods A similar procedure was advised by Goudie et al� under running water, during which we washed (1981; 143)� due to repeatable measurements with away all small particles of limestone� The final individual limestone tablets, we avoided such a elimination of fine particles was achieved in procedure by drying the tablets in a chemical phase 5, when the surface of the limestone tablets laboratory for 15 days� instead of drying in an approached closer to the natural roughness� oven, we implemented a correction factor for Afterwards, limestone tablets were dried in a the amount of water which remained in the chemical laboratory for 15 days� during this limestone tablets after 15 days of drying� The period of time the majority of water evaporated whole procedure from the preparation to final from the limestone tablets and the weight weighing of the limestone tablets is represented became only humidity-dependant (semi-stable)� in Fig� 2�1� Weighing (phase 7) was done with the analytical in phase 1 (Fig� 2�1) a core with a diameter balance Sauter 404/13 with resolution 0�1 mg and of 41 mm was cut into 5-8 mm slices� The accuracy of about ±0�4 mg� using this procedure probability of chipping at the edges was reduced 906 limestone tablets were prepared� in phase 2� drilling was done underwater� due After exposure, we gently cleaned the limestone to the fragility of limestone, a small hole with a tablets (phase 8) if this was necessary� Cleaning diameter of 4 mm was drilled through the tablet was usually done in cave streams� Phases 6 to 8 at the beginning and enlarged to 8 (9) mm from were applied at all times when the limestone both sides� This phase was followed by cleaning tablets were exposed to water in stream caves� 2.2.2 Test study An 8-month-long test of the methodology was are very low, as can be seen from the median done at 85 locations mainly on the high and (-1�5 µm/a) and the arithmetic mean (-7�4 µm/a)� low dinaric karst of Slovenia� Limestone tablets Values were strongly concentrated (more than were exposed to low and high water levels, at 32 % of measurement places) near the arithmetic some places to very harsh environments (e�g� mean in the class between -10 and 1 µm/a� At 44 Škocjanske Jame)� Shortly after installation % of measurement locations, rates are too small limestone tablets were affected by very high to be reliably detected with MEM within 10 years! discharges since the amount of precipitation The large difference between the arithmetic mean exceeded the 10-year recurrence interval� and the median shows some relatively high out-Limestone tablets were attached to cave walls standing values� The highest dissolution rates are with an iron screw with nut and felted washers stronger than -100 µm/a and the highest sinter/ (Fig� 2�2)� Later on, testing of the methodology tufa deposition rates over 100 µm/a� was also done parallel to measurements on study due to similar meteorological conditions in cases (Chapter 3)� the laboratory during weighing before and after The results are presented and discussed in de- exposure, the influence of relative humidity on the tail by Prelovšek (2009) – here only some meth- tablets’ weights can be neglected, but in different odological experiences are highlighted since they meteorological conditions can be important� were important for further measurements (study Some limestone tablets that were exposed to cases; Chapter 3) and error estimation� The pre- allogenic streams were damaged by corrasion/ vailing process was dissolution but sinter deposi- abrasion; therefore, actual dissolution rates tion should not be neglected since this prevailed are lower� Bed load material makes, due to the at more than 20 % of measurement places� Rates chipping of edges, results irrelevant and unusable� 18 Research Methods The highest dissolution rates were characteristic passage� For example, in Lekinka cave, the for Krka’s right tributaries, where measurements dissolution rates greatly weaken with height, were usual y performed at il uminated springs� although all limestone tablets were flooded Nearby measurements in stream caves, where (though at the highest level for a very short time)� dissolution rates were much weaker, and due to the use of iron screws, nuts and washers, visual etching on the limestone tablet’s surface, excessive dissolution due to iron oxide was proved that they were significantly altered by observed at several measurement points� Since biocorrosion, which was also evident at some it occurs very randomly and without noticeable other measurement places� Measurements at logical explanation (even along the same stream), springs and in stream caves behind them can it cannot be easily predicted and theoretical y show very different values� quantified for other measurement places� The Very different local factors result in very problem can be avoided by using stainless steel different local dissolution rates� The highest (inox) or plastic screws, nuts and washers� spatial variability was observed between Lekinka Resistance of limestone tablets to fast flows cave and Postojna cave system, where the ratio (e�g� Škocjanske Jame) and precision was of dissolution rates amounts to 36:1, even though satisfactory to the point where it was appropriate the caves are less than 1 km apart� Another to continue measuring� Nevertheless, to very important dissolution rate factor is related improve the precision of the methodology some to vertical microlocation in the underground corrections are suggested in the following chapter� Figure 2.2. Limestone tablet fixed on iron screw. 19 Research Methods 2.2.3 Measurement errors and correction factors Measurement errors present a deviation from formed by Gams (1985) and advised by Goudie real values� Knowing of errors and using et al� (1981; 143), and humidity conditions sig- correction factors should substantially improve nificantly changed through each year in the precision� The latter is appreciated while laboratory, correction of weight relating to rela-measuring underground since dissolution and tive humidity is crucial to avoid deviation due to sinter deposition rates are usually in the range of changes of relative humidity� This can be done several (tenths of) µm� with the equation in Fig� 2�3B, which was de- rived with linear regression analysis on the basis Deviation due to changes of relative humidity of a strong and positive Pearson product corre- Limestone is a porous sediment and therefore lation coefficient (+0�62; N=147) between weight easily absorbs water from or emits water into change and relative humidity� Application of the the air until equilibrium with the atmosphere correction factor for relative humidity signifi-is achieved� This is well known and can be seen cantly reduces (up to 5�8 mg) high seasonal vari-from seven limestone tablets that were stored in ation in the weight of 20-25 g limestone tablets the Chemical Analytical Laboratory of the Karst (about 0�7 µm in metric unit) if relative humidity Research institute and weighed 147 times dur- varies between 36 and 67 %� using this equation, ing changeable humidity conditions (Fig� 2�3A)� the calculated weight can still deviate from real Since we avoided the drying of limestone tablets values on average ±0�3 mg (about ±0�03 µm) and in an oven and cooling in silica gel1, as was per- up to ±1�1 mg (about ±0�12 µm), which is most Figure 2.3. A - Annual and sub annual variation of relative humidity and deviation of weight from primary defined (initial) value of seven limestone tablets (average); B - Relation between relative humidity and deviation of weight from primary defined weight. 1 This was done to (a) simplify and (b) speed up the procedure and (c) due to multiple cyclic use of two limestone tablets (see Chapter 3), when several times repeated drying of tablets cause intensive migration of saturated water to the surface of limestone tablets and structural modification of limestone tablets (e.g. case hardening). 20 Research Methods Figure 2.4. Comparison of dissolution and sinter deposition rates on limestone tablets fixed to the cave wall with different materials at Križna Jama 2 (A-final cumulative values; B-growth of differences in time). probably a sum of the balance error, the error of beginning, the material for fixation was made defining relative humidity and the error of some of iron that resulted in rusting and accelerated measurements when humidity in the limestone weight loss (Fig� 2�4)� tablets was not well equilibrated with relative The rusting of iron screws, washers or nuts humidity in the air� instead of using the equa- and the contact of rust with limestone can rep-tion in Fig� 2�3B, we can place, but not expose resent a significant problem for reliable dissolu-to water, several limestone tablets beside exposed tion and sinter deposition rate measurements� ones, and after exposure treat them as exposed Contact of rust with limestone probably forms and observe their weight change (initial weight siderite (FeCO3), which enhances acidity (Ford and weight after exposure should be the same)� &Williams 2007; 58) and accelerates dissolu- tion� if the sinter deposition rates are very weak, Deviation due to formation of iron oxide rusting sometimes turns weak sinter deposition Limestone tablets used in this study differ sig- rates into misleading dissolution rates� Acceler-nificantly from others previously used due to the ated dissolution, as a result of rust, can be seen central hole for fixation� Other researchers, who under a magnifier as a circular entrenchment at were measuring dissolution rates in streams, usu- the surface of a limestone tablet, especially below ally used nylon cages (Newson 1971 after Gunn the edge of washers or as an incomplete solution 1986; 383, Trudgill 1975 after Gunn 1986; 383), over all areas of limestone tablets located under meshes size 63 μm (Goudie et al� 1981; 143) or the felted washers� plastic wires (Gams 1986) to fix limestone tablets Rusting, and its influence on dissolution to the cave wall� This can result in higher abra- rates, is not expressed equally at all measure-sion rates (at least of weakly attached crystals ment points� in Križna Jama and Križna Jama when cement around them is partly dissolved), 2, a comparison of tablets fixed on stainless steel which was avoided in our study by firm fixa- screws, nuts and washers shows that calculated tion with screws, nuts and felted washers� At the rates of misleading dissolution can amount from 21 Research Methods -0�1 to -2�4 µm/30 days� The lowest average and average through the year can be much stronger the lowest monthly maximum misleading disso- (from -0�3 to -0�6 µm/30 days)� These values are lution rate (up to -0�1 µm/30 days) in Križna Jama so high that they show dissolution instead of real was detected in Pisani Rov (variegated passage) sinter deposition, at least in Križna Jama 2� near Kalvarija and at Brzice (rapids) downstream Since the rusting of iron represented a from the first lake of Križna Jama (for plan see big problem especially when dissolution or Fig� 3�1�6 on page 40)� The highest calculated sinter deposition rates were weak, stainless maximum misleading dissolution rate was de- steel or plastic should be used instead of iron� tected in the upstream part of Jezerski Rov (lake Synchronous measurements with limestone passage), with amounts up to -2�4 µm/30 ays� in tablets fixed on stainless steel screws and PVC Križna Jama 2, the maximum monthly mislead- plastic screws, which were used in Križna Jama 2, ing dissolution rates are smaller in comparison showed little difference between stainless steel with Križna Jama (up to -1 µm/30 days), but the and PVC plastic� Figure 2.5. To transport limestone tablets through the harsh underground environment, a special carrier was designed to prevent physical damage (photo: Alojz Troha, DLKJ). 22 Research Methods Deviation due to transportation damages Trudgil et al� 1994), a freshly cut surface has damage to limestone tablets was avoided by some influence on dissolution rates� Gams (1985; using a specially designed carrier (Fig� 2�5) in 372) found that dissolution rates may be, due to which limestone tablets were arranged in several a fresh cut surface, weaker in the first year and layers� Each limestone tablet within each layer remain constant during a second and third year of was separated from other limestone tablets by at measurements� A contradictory phenomenon was least 5 mm to avoid any contact between them� observed by Trudgil et al� (1994) – in the first two Between layers, limestone tablets were separated years dissolution rates were a magnitude higher with felted washers to prevent damage from in comparison with later observations that lasted abrasion� Plastic foil with the tablets’ numbers eight years� The decrease of dissolution rates was under each layer of limestone tablets enabled interpreted either as a “rapid erosion of exposed identification of each, since they were not directly crystals at first and the formation of a less soluble designated� No damage during transport was weathering crust at a later stage” or as a result of detected during 6 years of use� the cleaning process� in addition, it is possible that the drier years in the second period of observation Deviation due to freshly cut surface could have decreased dissolution rates� According to some warnings (Šušteršič-personal Our study of dissolution rates carried out in comm�) and field experience (Gams 1985, Lekinka showed a weakening of dissolution rates Figure 2.6. Differences in dissolution rates due to freshly cut surfaces and heterogeneity of limestone tablets (positive deviation shows higher dissolution rates on fresh limestone tablets). Each measurement lasted about 15 days. 23 Research Methods (Fig� 2�6), since the strongest dissolution rates with the dissolution of partly broken crystals or were observed on freshly exposed limestone tab- calcite cement with a greater reaction surface� lets, while the others had already been exposed The influence of freshly cut surfaces on sinter for about 540 days (in this period dissolution deposition rates was studied at the downstream already removed at least 32 µm of the limestone end of Pisani Rov (Križna Jama; Chapter 3�1�5), tablet’s surface)� The highest difference between where deposition rates are among the high-limestone tablets was observed at the beginning est detected in cave streams of Slovenia� Two of measurements (the difference amounted to pairs of old and new limestone tablets were used more than 2 µm/15 days)� When dissolution had for measurements� Each measurement lasted removed 25 µm of the limestone tablet’s surface, 30 days� Before placing new limestone tablets, the limestone tablets indicated similar dissolu- old ones were exposed for 490 days (during this tion rates� This was a result of changes on the period 21 µm of sinter was already deposited on reaction surface, which was modified with a cut old limestone tablets)� On-going synchronous into the crystal lattice� After dissolution of many measurements point out that differences in sin-small (probably partly broken) crystals with high ter deposition rates exist only at the beginning of specific areas, reliable dissolution rates followed measurements (up to 3 µm/30 days) until about on the undamaged crystal lattice� At the latter 3-5 µm of sinter is deposited (Fig� 2�7)� Later, surface of crystals, dissolution “passes from one sinter deposition rates are nearly equal since the atomic layer to the next, much like unravelling standard deviation amounts to only 0�3 µm and successive rows of knitting” (Ford & Williams the minimum and maximum are within ±1 µm 2007; 66)� This is a slower process in comparison span� Figure 2.7. Differences in sinter deposition rates due to freshly cut surfaces and heterogeneity of limestone tablets’ surfaces (positive deviation shows higher sinter deposition rates on old limestone tablets). Each measurement lasted about 30 days. 24 Research Methods Deviation due to heterogeneity of limestone only -0�1 µm/15 days; Fig� 2�6)� deviation due tablets to heterogeneous surfaces of limestone tablets Although limestone tablets are made of the same where sinter deposition prevails are even lower type of limestone, they display a certain degree (Fig� 2�7)� of heterogeneity� Gams (1985) did not devote any special attention to this problem although he vi- Deviation due to different lithology sual y recognized heterogeneity of limestone it- use of standard limestone tablets in different self, from which the tablets were prepared� Like caves provides comparable measurements of wa-Crabtree & Trudgill (1985), he avoided this prob- ter aggressiveness and not necessary dissolution lem by using similar limestone, if possible from rates in that cave� if we apply measured dissolu-the same stratigraphic horizon� According to our tion rates to a cave where measurements took observation, even limestone from the same strati- place, we have to take into consideration different graphic horizon consists of different portions lithological characteristics that influence dissolu-and compositions of allochems (biogenetic rem- tion rates� Therefore, measurements of dissolu-nants - shel s, peloids and intraclasts) and differ- tion rates on different lithology have to be made ent portions of micrite with different degrees of to apply measurements with tablets made of Lip-recrystallization� Since sparites and other coarse ica limestone to the present-day speleogenesis of grained rocks are less soluble than pure micrite, that particular cave� we should expect different dissolution rates� Gams (1966b, 1980) states that the hardness Many studies have found that micrites and bio- of waters from dolomite does not differ much micrites show higher dissolution rates and that from that which flows through limestone� This rates of dissolution weakens substantial y where would suggest similar dissolution between sparite becomes greater than 40-50 % by volume dolomite and limestone, as was recognized (Sweeting & Sweeting 1969 after Ford & Williams also by Sweeting (1972; 29), who interpreted 2007; 28, Maire 1990 after Ford & Williams 2007; similarities with sufficient residence time of 28)� dissolution rates also increase with the het- water to reach equilibrium (Sweeting 1972; 29) erogeneity of grain size since differences in grain and a higher degree of fracturization in dolomite, size result in greater roughness (reaction surface) which enhances dissolution with greater reaction – this is the reason for weaker dissolution rates in surface� The amount of dissolved carbonates also pure micrite (Ford & Williams 2007)� Although reflects the residence time of waters and this Lipica limestone seems to be quite homogeneous, significantly increases the difference between the we should still expect some differences in disso- amount of dissolution and dissolution rates� The lution rates� major role in dissolution rates is played by the in Fig� 2�6 we can see two pairs of differences kinetics of dissolution, which is without doubt between new and old limestone tablets� The first slower in dolomite (Gerstenhauer & Pfeiffer positive deviation (higher dissolution rates on 1966 after Sweeting 1972; 28-29, Chou et al� 1989 new limestone tablets) is already described as a after dreybrodt 2004; 297-298, dreybrodt 1988; deviation due to a freshly cut surface� Further 179) due to bigger crystals and stronger bonds on, deviation mostly derives from heterogeneity between MgCO3 molecules (Ford & Williams of limestone tablets and can amount on average 2007; 71)� differences are evident especial y to ±0�5 µm/15 days� The maximum observed at low saturation (up to 50-60 %), while at deviation amounts to -1�6 and 0�7 µm/15 days� higher degrees of saturation differences seem Nonetheless, two pairs of limestone tablets to decrease (dreybrodt 1988; 179, dreybrodt & indicate over 399 days of measurement similar Eisenlohr 2000; 145)� differences in dissolution average dissolution rates (the difference is rates appear also within different types of 25 Research Methods Figure 2.8. Dissolution rates according to different lithology of tablets. limestone, since they contain different amounts nian karst� Results represented in Fig� 2�8 show of “impurities”, different types and amounts of that all limestone demonstrates similar dissolu-allochemical grains, different cements (micrite/ tion rates� deviation from Lipica limestone (K 32) sparite) and different primary porosity� Regarding is rather small and amounts to up to 20 %� Lower some examinations, Sweeting (1968; 229) states dissolution rates were observed with marble that limestone which has a percentage of sparry from Pohorje mountain (PZ marble), with dolo-calcite, may be less soluble than micrites, most mite from the dolenjska region (J2 dolomite) and probably because of their larger crystals� especial y with Middle-Lower Jurassic, Lower To compare dissolution rates of different rocks, Jurasic and upper Triassic dolomites sampled in observation of dissolution rates between several or near Križna Jama (J 2+3 1,2, J1 and T3 dolomite)� carbonate rocks was done in Lekinka where satu- The latter dissolves up to 90 % slower than Lip-ration of water ranges from low to high� Some ica limestone� Higher dissolution rates were ob-carbonates were taken from caves that were cho- served with fractured limestone (K 22 limestone) sen as case studies (Chapter 3; Križna Jama, Le- due to a greater reaction surface� deviation with-kinka cave, Postojna cave system), while some in each rock sample is relatively small – on aver-others were taken randomly, usual y from Slove- age it amounts to 7�7 %� 2.2.4 Absolute precision of measurements with limestone tablets – comparison with MEM measurements According to Jennings (1981 after Spate et al� achieved� Our comparison of MEM measure- 1985), good agreement between limestone tab- ments and measurements with limestone tablets let experiments (-17 µm/a) and micrometer took place in Lekinka cave for dissolution rates measurements (-21 µm/a) in absolute terms was and in Križna Jama for sinter deposition rates� 26 Research Methods Figure 2.9. Differences in dis- solution between MEM meas- urements and limestone tablets recorded in Lekinka. in Lekinka cave, differences of dissolution periods stronger dissolution rates were found rates were measured at the same place on the using MEM� it is important that some minimal same type of a rock� in each of 4 measurement values measured with MEM can be equal to periods, 9 values per measurement period were average values measured with limestone tablets� defined by MEM and 3 values for limestone The highest discrepancy (1:0�41) was observed tablets (Fig� 2�9)� All deviations described and during the third measurement period, in which calculated in the previous chapter were taken limestone tablets were partly buried under the into account and for that reason avoided to bed load material� This partly prevented them improve the precision of measurements and from dissolution� Nevertheless, the second and comparisons� Only during the first measurement the fourth measurement periods indicate that, period was the dissolution rate stronger with even when the conditions are equal, the average limestone tablets� Later, during all measurement dissolution rate measured with limestone tablets Figure 2.10. Comparison of dis- solution/sinter deposition rates between MEM measurements and measurements with lime- stone tablets recorded at Brzice (Križna jama). 27 Research Methods is by about 33 % lower in comparison with the differences of sinter deposition rates were average dissolution rate measured by MEM� A measured in Križna Jama� in each of 3 meas- similar deviation in the same direction was found urement periods, three values per measure-by Jennings (19 %; 1981 after Spate et al� 1985)� ment period were defined by MEM and one On the basis of these results it is very likely that value for limestone tablets� MEM measurements higher values defined by MEM are overestimated were done on natural sintered channel bottoms and a result of probe erosion, which can result while measurements with limestone tablets were in more than 20 µm higher “dissolution” per done with limestone tablets already exposed to reading even on hard limestone (Spate et al� 1985; saturated waters in Križna Jama for 247 days� 431)� Since we were measuring on wet surfaces Fig� 2�10 shows that methodological discrepan-that are relatively softer in comparison with dry cies in the case of sinter deposition are much ones, higher probe erosion is to be expected� higher than those in regard to dissolution� The Fig� 2�9 also provides us good insight into the highest difference was observed during the first maximum span of measurements using MEM measurement period (using limestone tablets we and limestone tablets� The average standard de- detected only 8 % of flowstone deposition meas-viation and maximum span using limestone tab- ured with MEM)� Later, differences are lesser lets is at least 5-times smaller in comparison with (during the second measurement period, using MEM measurements� This difference arises from limestone tablets we detected 50 % of flowstone microlocal differences in dissolution, which are deposition measured with MEM)� differences averaged using limestone tablets, since the dis- can arise from already established calcite crys-solution rates are calculated from weight loss and tal lattice on natural sintered channels and from reaction surface� When using MEM, differences roughness of the rock surface, which influences reflect real differences in dissolution between the thickness of the diffusion boundary layer� several measurement points at the rock surface The latter is thinner on rough natural surfaces due to microscopic heterogeneity of the rock� and deposition rates are therefore higher� 2.3 HYDROCHEMICAL METHOD The hydrochemical method was often used to ob- ness (in carbonate waters generally CaCO3 and serve chemical denudation rates� The method is CaMg(CO3)2), continuous measurements of dis-based on differences of solute load between input charge and SEC are valuable for chemical denu- (surface) and output (resurgence) and observa- dation rates where SEC<600 μS/cm and where tion of discharge (White 2000; 151)� if an aquifer pollution is not problematic (Ford & Williams is recharged by primary infiltration, input solute 2007; 83 & 63, Toran et al� 2006)� Nonetheless, load is usually neglected and only discharge and to check the reliance of data (especially solute solute concentrations are measured at the spring� concentration), some laboratory analyses and if we are dealing with at least a portion of allo- discharge verifications are essential� genic input, consideration of the latter is of cru- if observations are done at the resurgences, cial importance� denudation rates are related to the whole catch- Since measurements of specific electrical con- ment area, but such measurements do not pro-ductivity (SEC) are more easily obtained than vide any information on spatial variability, chemical analysis of water samples and SEC is which can be considerable within the aquifer� in a relatively good approximation for total hard- our case studies (Chapter 3), the dissolution rate 28 Research Methods was calculated using changes of SEC (~change in sition rates, reaction surface and transit time are solute load) between two measurement points, crucial to convert downstream change of SEC where confluences (and diffluences) are absent� into metric rates� Since such measurements were downstream increase of SEC can be interpret- done only occasionally they show momentary ed as dissolution and decrease of SEC as sinter rates of processes and not cumulative ones as do deposition� To define dissolution or sinter depo- limestone tablets or MEM measurements� 2.4 OTHER COMPLEMENTARY METHODS Concentration of Ca2+ and Mg2+ in water sam- rate measurements are crucial for a proper deples were determined by complexometric titra- termination of carbonate balance� if we mistake tion with 0�01 M EdTA in the chemical ana- the correct pH value for 0�1, the saturation index lytical laboratory at the Karst Research institute with respect to calcite will be wrong by nearly the ZRC SAZu, Postojna� due to relatively pure same value (Sasowsky & dalton 2005; 127)� pH Ca-Mg-CO3 waters, Mg2+ concentration was de- measurements were done using a WTW Multi- fined as the difference between total hardness line P4 and a plastic body pH probe� in situ meas- (Ca2+ and Mg2+) and calcium hardness� Carbon- urements were taken in calm or slowly flowing ate alkalinity (usually HCO -3 in our cases) was water� Calibration of the pH meter was done in determined at the same location by potentiomet- the chemical laboratory with pH = 7 and pH = 10 ric titration with 0�02 N HCl with an end-point buffer solutions� due to the high number of meas-at pH = 4�5� Often, Ca/Mg ratio was determined urements and complicated nature of calibrating using Ca2+ and Mg2+ concentrations� in caves we practiced calibration in the labora- Specific electrical conductivity (SEC) can tory instead of the proposed calibration at each provide, in relatively pure carbonate water so- measurement place� The resolution was 0�01 of pH lutions, a good approximation of dissolved load value� Accuracy was estimated to be ±0�05� (Ca2+ and Mg2+ concentrations; White 2000; water temperature was determined with a 145)� Consequently, its change during water WTW Multiline P4 and an SEC probe, which course reflects the degree of interaction with also supports temperature measurements� Reso-soluble rock or the degree of flowstone deposi- lution and precision was 0�1 °C, while accuracy is tion� For defining spatial and temporal changes supposed to be ±0�2 °C� of dissolved load we used a WTW Multiline P4 Saturation index with respect to calcite (SIC) and SEC probe� Resolution was 1 μS/cm, accu- and dolomite (SID) indicates aggressiveness of racy estimated to be ±2 μS/cm� SEC was always water with respect to calcite or/and dolomite� measured in situ� in the case of SiC, the saturation index depends pH measurements show a concentration of H+ on activity concentrations of Ca2+ and HCO -3, (or H - 3O+) ions in water� Since the H+ ions act ag- K2 (which is a constant for decay of HCO3 into gressively to solid CaCO 2- 3, pH is one of the most H+ and CO3 ), KC (which is a constant for decay important parameters of water in karst terrains of CaCO 2- 3 into Ca2+), activity of CO3 , pH value, (Roques 1969; 144)� Concentration of H+ ions de- temperature and some other ions in the solution pends on reaction with rock and air and on re- (Ford & Williams 2007; 48-49, Meadows 2000; actions within solutions� Since the influence of 68)� if it is lower than -0�1, water will dissolve H+ concentration to saturation index, which was calcite but if it is higher than 0�1 water tends to calculated also using pH value, is high, its accu- deposit CaCO3� Between -0�1 and 0�1, water is 29 Research Methods more or less inactive� SiC and Sid were calculated able (Škocjanske Jame, Postojna cave system) or using the computer program WATEQ4F (Ball & with digital level loggers where other hydrogeo-Nordstrom 1991)� input parameters were SEC, T, logical research was done at the same time (Pos-pH (determined in situ), concentration of Ca2+, tojna cave system, Škocjanske Jame)� concentration of Mg2+ and carbonate alkalinity Between 21 March 2007 and 17 October 2007 (defined in the chemical laboratory)� Gealog S was used in Križna Jama for determin- To define the stage-discharge curve, dis- ing water level, water temperature and SEC� Res-charge was measured at different water levels olution for SEC and T was the same as resulted using the salt-dilution method (Käss 1998)� This from measurements done by the WTW Multi-involves the preparation of solute (usually sodi- line P4� Because of questionable long-term sta-um chloride-NaCl), injecting the solute into the bility, estimated accuracy was slightly lower (for stream and determining its dilution at a down- SEC ±5 μS/cm and for T ±0�2 °C)� discharges stream measuring point� A time dependant were calculated using continuous water level NaCl concentration curve defined with an SEC data and a stage-discharge curve determined us-meter (WTW Multiline P4) and mass of salt at ing the salt-dilution method� the downstream point, where the solute becomes Air CO2 concentration was determined using uniformly mixed with stream water, provides us Vaisala’s hand-held carbon dioxide meter GM70, enough information about discharge� For a given which consists of the indicator and GMP222 volume or rate of injection, greater stream dis- CO2 probe� The latter had a resolution of 20 ppm charges will result in greater salt dilution and and accuracy of ±1�5 % of range + ±2 % of read-lower concentrations measured at the down- ing (Vaisala’s Technical data 2007)� Since the stream site and vice versa� range of a probe was between 0 and 3,000 ppm, Height of water level was obtained either with accuracy was always better than 105 ppm� Better periodical visual observations of water gauges results were obtained with longer measurements (Križna Jama, Lekinka cave), from the Slovene at individual measurement points and the calcu-Environmental Agency where data were avail- lation of an average� 30 CASE3 STudiES Results obtained during the 8-month-long test differences in rates of karst processes already study (Chapter 2�2�2) showed that additional, proposed by Trudgill (1975 after Gunn 2004; more frequent and spatially widespread 322)� Seasonal or even monthly fluctuation measurement can be done at several places using of dissolution or sinter deposition rates at the limestone tablets where the dissolution or several measurement places can lead toward sinter deposition rates are sufficiently strong� better understanding of spatial and temporal More intensive measurements with shorter factors that control the present-day genesis of measurement periods can indicate seasonal selected caves� Nevertheless, we also took into Figure 3.1. Location of case studies (numbers of sites are equal to chapters). 31 Case Studies consideration some caves which are important rates as a result of allogenic recharge from due to their (inter)national recognisability or the Pleistocene accumulation terrace of their special geomorphic or hydrologic function� Nanoščica/Pivka), pages 75-98; From these points of view the following caves 3.3 Škocjanske Jame (where there is an (cave systems) were chosen for more intense excellent example of an underground gorge research: of the Reka River, which is characterized by extreme power of allogenic recharge 3.1 Križna Jama-Križna Jama 2 cave system at middle-high water levels and extensive (well ventilated subhorizontal cave system flooding at very high water levels), pages in an epiphreatic zone with high sinter 99-112; deposition rates; in Križna Jama 2, present- 3.4 Postojna basin-Planina polje cave system (a day speleogenetic processes have not yet long and regionally important underground been studied), pages 33-73; network of dry and hydrologically active 3.2 Lekinka cave (a subhorizontal stream subhorizontal passages of Postojna cave cave with exceptionally strong dissolution system and Planinska Jama), pages 113-126� 32 3.1 KRIžNA JAMA-KRIžNA JAMA 2 CAVE SYSTEM Križna Jama (cave of the cross; Reg� No� 65) interested in allochthonous sediment in Jezerski is a cave recognized by its high biodiversity Rov (lake passage) and Pisani Rov (variegated (45 defined troglobionts – 4th place in the passage)� in the 1980s, the first dating of Ursus world; Culver & Sket 2000) and more than spelaeus deposits by u/Th dating was done by 2,000 excavated Ursus spelaeus bones from the Ford and Gospodarič (1989)� The last datings of end of the 19th century� it is also a recognizable allochthonous sediments in Križna Jama were touristic cave due to its several underground done by Pohar et al� (14C; 2001) and Zupan Hajna lakes along the cave stream� The hydrological et al� (paleomagnetism; 2008)� The morphology continuation of Križna Jama (Križna Jama 2) is, of passages was studied scientifically for the first due to fragile rimstone dams, on the list of six time by Gospodarič (1974) and later by Slabe highly protected caves in Slovenia and accessible (1989, 1989, 1992)� The first one to measure only with special permission from the Ministry processes was Mihevc (1997), who measured of the Environment and Spatial Planning� sinter deposition rates at three places between Scientific research was first undertaken the first lake and Ponor� here by Hochstetter at the end of 1870s� At the Križna Jama 2 (Reg� No� 6286) has a much same time, the first detailed map of Glavni Rov shorter history of research since the entrance was (main passage) to the first lake was made by the dug out successfully only in 1991� Before 1991, the geodesist Szombathy� Hochstetter investigated entrance was blocked with boulders at the edge the cave primarily from the paleontological of the collapse doline that separates Križna Jama point of view, but he described the cave in detail and Križna Jama 2� The only published work is a and mentioned some geomorphological features: brief description provided by drole (1997), who flowstone coating in the water channel near led the cave survey� Ponor, the “erosional” cross-section of the same channel, etc� The first to relate the formation of Geological and geomorphological Križna Jama passages to dissolution was F� Kraus characteristics (1894)� Between the First and Second World Križna Jama and Križna Jama 2 are typical Wars, investigations in the cave were primarily stream caves in an epiphreatic zone� They are dedicated to the exploration and survey of located in the centre of a triangle between passages upstream from the first lake� Some Bloke plateau (~720 m a�s�l�), Cerknica polje basic speleogenetic observations were done by (~550 m a�s�l�) and Lož polje (~570 m a�s�l�)� The cavers of društvo za raziskovanje jam Ljubljana majority of nearly horizontal water passages are (Society for Cave Exploration Ljubljana; Planina developed between 577 m a�s�l� (the lowest sump 1965, Puc 1986)� in the 1960s, Novak (1966, in Križna Jama 2) and 630 m a�s�l� (spring under 1969, 1990) traced the stream in Križna Jama the ending breakdown in the Blata passage in twice and confirmed its water connection with Križna Jama)� The main trunk passages (Glavni Šteberščica spring� Later, Gospodarič (1974) was Rov, Pisani Rov and the Blata passage) are on 33 Case Studies - Križna Jama-Križna Jama 2 cave system average 10 m wide and usually more than 5 m latter prevail in the southern part of the Bloke high� Where passages cross well fractured rock, plateau� Lower Triassic dolomite is due to thicker several collapse chambers developed (for example layers of impurities usually impermeable for Kalvarija (calvary), Križna Gora, Kristalna water� The permeability of dolomite rises toward Gora (chrystal mountain), collapse chambers upper Triassic (Norian and Rhaetian) rocks, in the Blata passage, and the Kobe chamber in but in the latter tectonic deformation plays an Križna Jama 2)� Where flowing water is absent, important role regarding permeability� if they the rocky cave floor is covered by allochthonous are strongly tectonized, their permeability is sediments, breakdown material or speleothems� close to Lower Triassic dolomite� Ponors of major Water passages are characterized by stagnant superficial streams at Bloke plateau (Bloščica, water bodies (lakes) and the flowing water Farovščica and Studenec pri Ravnah) are in between them� Lakes are usually formed behind upper Triassic dolomite (see Fig� 3�1�2)� Caves are rimstone dams� very rare even in upper Triassic dolomite, since The surface above Križna Jama is highly its low resistance to physical weathering usually karstic with (elongated) conical hills and produces parallelepipedic gravel (Pleničar 1953) closed depressions without superficial streams� that blocks underground passages especially Relative elevation amplitude between hills and near the surface� All along superficial streams we depressions can amount to as much as 200 m� can find fluvial deposits� The thickness of the vadose zone below the karst Lower Jurassic dolomite (and partly surface ranges from 10 to 270 m� limestone) has very similar characteristics Northeast of this karst surface, is the levelled to upper Triassic dolomite� Since they are Bloke plateau� Since the lowest levelled surface composed of cemented fine-grained particles, of the southern Bloke plateau is occasionally incomplete solution produces fine-grained sand, flooded, Bloke plateau can be treated also as a which is incorporated in the soil matrix� Such border polje (Gams 2003; 330)� it seems that the residual dolomitic “sand” may inhibit further surface at Bloke plateau was similar to the area karstification (Bogli 1980 after Gunn 1986)� The above Križna Jama in the past until the area of upper part of the Blata passage in Križna Jama is Bloke plateau reached the piezometric level� At already located in Lower Jurassic dolomite� that time, dissolutional lowering stopped at the Lower-Middle Jurassic limestone is the host piezometric level� due to continued denudation rock for the majority of Križna Jama’s passages of hills, the area of levelled surface on Bloke (Fig� 3�1�2)� According to Folk’s classification, this plateau progressively expanded� The southern limestone is classified as micrite and oomicrite� part of Bloke plateau was also influenced by Well-developed karstification of this limestone allocththonous material, which was carried from results in a lack of any superficial streams and the northern Bloke plateau by Bloščica stream� springs� due to partial secondary dolomitization, West of the Križna Jama-Križna Jama 2 cave dolomite layers, lenses and nests can be found system is Cerknica polje� it can be considered within Lower-Middle Jurassic limestone� in the a well-developed over flow polje where Bloke Middle Jurassic rocks, dolomite can completely plateau and the area nearby Križna Jama-Križna prevail� Jama 2 cave system represents its catchment The most important tectonic feature in the area area� The genesis of Cerknica polje is related to of Križna Jama-Križna Jama 2 cave system is the the idrija fault zone, which crosses the polje in a syncline between Bloke plateau and Notranjsko NW-SE direction� podolje (Notranjska lowland) and the idrija fault The northern Bloke plateau is made up of zone (Fig� 3�1�1)� The entrance of Križna Jama Lower, Middle and upper Triassic rocks� The lies only 1 km NE from the syncline’s axis� in 34 Case Studies - Križna Jama-Križna Jama 2 cave system the longitudinal section (NW-SE), the syncline Ljubljana marsh� Superficial streams on the Bloke begins near Cerknica and continues through plateau receive water from many small springs� Križna Jama toward the syncline between Lož Since water collects in well-fractured dolomite, polje and the closed depression of Loški Potok the average hardness of water is high (13�9 ºN) (Gospodarič 1974)� (Gams 1966, 2003; 73)� A minor portion of water Although Križna Jama and Križna Jama 2 is derived from surface runoff which is also, due lie several kilometres from the idrija fault zone, to thin carbonate soils, quite hard� The majority of the carbonate massif between Bloke plateau, water is collected in the Bloščica and Farovščica Cerknica polje and Lož polje did not suffer any streams� According to Gospodarič & Habič’s important fault deformation� There is some (1976; 49) measurements, the minimal discharge evidence of minor tectonic movement near of Bloščica between 1972 and 1975 amounted to Križna Jama, for example the fault-junction of 0�02 m3/s, the average discharge 0�42 m3/s and the upper Jurassic dolomite which borders Middle maximal discharge was 15�9 m3/s� due to similar Jurassic limestone in the axis of the syncline characteristics but a much smaller catchment (Fig� 3�1�1; Gospodarič 1974)� Relatively slight area, the average discharge of Farovščica should tectonic deformations are also observed in be about 0�09 m3/s� At low-middle water levels Križna Jama� the ponors of Bloščica lie near Velike Bloke� At high water levels Bloščica continues as a Hydrological characteristics superficial stream toward Nova Vas, where it From a hydrological point of view, the Križna joins Farovščica stream and they sink together Jama-Križna Jama 2 cave system lies between near the Fara settlement� three differently elevated and occasional y On the basis of past tracer tests (Fig� 3�1�2; flooded levelled surfaces (two poljes and a Šerko 1946; 126, Novak 1966, 1969, 1990, plateau)� Between them, the well karstified area Kogovšek et al� 2008), it is known that Bloščica spreads without superficial streams of water and Farovščica appear on the surface again at the (Fig� 3�1�2)� Therefore the aquifer between the eastern edge of Cerknica polje (in Štebrščica and levelled surfaces is fed by allogenic and autogenic Žerovniščica springs)� A minority of water flows recharge� toward two springs at Podlož but not toward the Because of its high elevation, Bloke plateau spring in Lož at Lož polje (Kogovšek et al� 2008)� was considered by Gams (2003) to be a roof The mean Štebrščica (1�30 m3/s) and Žerovniščica of the Notranjska karst – the water flows to discharges (0�21 m3/s; Gospodarič & Habič 1976; Cerknica polje, Lož polje, Ribnica polje and the 49) are much higher than those of Bloščica and Figure 3.1.1. Schematic geological cross-section perpendicular to the syncline’s axis (modified after Gospodarič 1974). 35 Case Studies - Križna Jama-Križna Jama 2 cave system Farovščica� The comparison of mean discharges test was done before the discovery of Križna of superficial input to the aquifer between Bloke Jama 2 (1991), the connection between Križna plateau, Cerknica polje and Lož polje (Bloščica Jama and Križna Jama 2 was never confirmed by and Farovščica) on one side and outflows from a tracing test� Similar physical characteristics of the aquifer (Štebrščica and Žerovniščica) on the water, the short distance (242 m), charcoal another side shows that about 66 % of the findings, ursus spelaeus bones found in Križna water derives from autogenic recharge� The Jama 2 and a similar quantity of water suggest contribution of Bloščica and Farovščica to the the continuation of the water flow from Križna aquifer was assessed at about 34 %� Jama through Križna Jama 2� Since we know that underground water flow downward from the water temperature in Križna Jama 2 deviates Križna Jama was never in question after the tracing slightly from that in Križna Jama (positively test conducted by Novak (1966, 1969) which in during summer and negatively during winter) Križna Jama confirmed the water connection with there must be a minor tributary between the two Štebrščica spring� Križna Jama 2 seems to be on caves� This was confirmed through a tracer test in the way of this water course but since the tracing 2007 (Kogovšek et al� 2008)� Figure 3.1.2. Hydrogeological map of the area between Bloke plateau, Cerknica polje and Lož polje with an emphasis on tracing tests (Šerko 1946, Novak 1966, Novak 1969, Novak 1990, Kogovšek et al. 2008). 36 Case Studies - Križna Jama-Križna Jama 2 cave system despite several tracing tests in the aquifer, the cave (Mrzla Jama pri Bločicah; more than 5 ºC; origin of the water in the Križna Jama – Križna for the location of this cave see the broken main Jama 2 cave system was unclear for a long time groundwater connection between Bloke plateau due to a lack of sampling in Križna Jama during and Cerknica polje in Fig� 3�1�2) also shows that the only tracing test in the hinterland of the caves at least at low-middle water levels allogenic water before 2007 (Šerko 1949; 128)� Springs which flows north and not through Križna Jama� feed the main water courses at Bloke plateau have The spine of the hydrological system in Križna a very low Ca2+/Mg2+ ratio, mainly very close Jama – Križna Jama 2 cave system are two streams to 1 (Kogovšek 1998)� Such a low ratio is a result from Pisani Rov and the Blata passage which join of infiltration entirely through upper Triassic together at Kalvarija and flow together through dolomite, which covers the catchment area of these Jezerski Rov in Križna Jama and most probably springs� Water in Križna Jama and Križna Jama 2 all along Križna Jama 2 (Fig� 3�1�3)� in Pisani Rov have a higher Ca2+/Mg2+ ratio (1�59-2�34 at the and the Blata passage, water appears under the first lake), which indicates the important portion ending breakdowns� Along the Blata passage, at of inflow through limestone� Such an inflow is least six tributaries were detected with SEC, T possible only through autogenic recharge in the and pH measurements� They contribute various neighbourhood of the cave system� if we also take quantities of water depending on the water levels; into account primary infiltration through Lower for instance the tributary from Tršanov Rov Jurassic dolomite in the upstream part of the cave (Tršan’s passage) contributes 92 % of all the water system, the portion of allogenic water should be in the Blata passage at middle water levels and very low in the Križna Jama – Križna Jama 2 cave less than 43 % at low water levels� it is important system� This was confirmed with a tracer test for water chemistry that nearly all tributaries end in 2007 at middle water levels from Farovščica as sumps or the water flows from narrow, very ponor – recovery of tracer was very low in Križna poorly ventilated passages� Jama (1�3 %, which is 3 g of 226 g injected uranin) Streams from Pisani Rov and the Blata passage and probably slightly higher in Križna Jama 2 join at Kalvarija� Regarding the six measurements (Kogovšek et al� 2008)� A very slight annual of SEC and temperatures at different water temperature variation in Križna Jama at the first levels (from HFirst lake = -4 cm to HFirst lake = 8 cm), lake (about 1 °C) and much higher in a nearby discharge from Pisani Rov and Blata is in the ratio Figure 3.1.3. Hydrological network of the cave system Križna Jama – Križna Jama 2 regarding visual observations and SEC, temperature and pH measurements at low and middle water levels. 37 Case Studies - Križna Jama-Križna Jama 2 cave system from 1:4�3 to 1:0�69� Although we are dealing the ending sump, Sifon upanja, we detected an with relatively small numbers of measurements, a underwater tributary which slightly changes the quite high Pearson product moment correlation physicochemical characteristics of the water� coefficient (0�68) suggests that with higher its contribution is, due to lack of discharge water levels contribution from the Blata passage measurements before and after confluence, increases� unknown� The most important tributary lies in Križna Jama, water final y disappears in the between Križna Jama and Križna Jama 2� At 70 m deep sump Kittlova Brezna (Kittl’s shafts)� middle water levels it was recognized as at least This connection was proven by a tracing test part of the underground Farovščica stream (Novak 1966)� in Križna Jama 2, water appears (Kogovšek 2007)� A portion of this tributary is after 242 m of underground flow from a more unknown� than 124 m deep sump and flows mainly as Height of water and discharge was observed free surface flow toward the ending sump Sifon in the first lake of Križna Jama (Fig� 3�1�4) at upanja (sump of hope)� Along this water course, measurement location KJ-2� At medium water the stream receives two tributaries, one from levels (HFirst lake ≈ 0 cm) discharge is about 0�1 m3/s� Kaplanov Rov (curate’s passage) that is according At HFirst lake = -7 cm outflow from the first lake to discharge very weak (at low-middle water ceases� According to extrapolation of the stage-levels it contributes about 1 l/s, which is less discharge curve, the highest observed discharge than 5 %)� A few tens of metres upstream from between 2004 and 2008 amounted to about 7 m3/s� Low discharge is characteristic for winter, when we observe retention due to snow, and for summer, when low amounts of precipitation are accompanied by high evapotranspiration� High discharge appear in autumn and spring� Meteorological characteristics The meteorological conditions in Križna Jama – Križna Jama 2 cave system are influenced mainly by outside temperatures and number of entrances� Air temperature is quite stable, in some part due to the temperature of water that is general y equilibrated with the temperature of the massif and amounts to 8�5 °C� Since Križna Jama has at least two openings, air flow occurs as a result of a chimney effect� intensity and direction of air flow in the cave is based on differences between outside and cave temperatures� Air flow is directed from the main entrance (Fig� 3�1�5) toward the Blata passage and Pisani Rov in winter and the opposite in summer� in winter, the flow of air into the cave significantly Figure 3.1.4. Gauging station in the first lake. A reduces temperatures in the entrance part of gauging station was also used for measurement Križna Jama and cave CO2 concentration� location KJ-2 where dissolution/sinter deposition The entrance to Križna Jama 2 is much was measured with 21 limestone tablets. smaller and artificial y enlarged to a diameter of 38 Case Studies - Križna Jama-Križna Jama 2 cave system about 0�5 m (Fig� 3�1�5)� in winter the air flow is sections of passages in Križna Jama 2 are bigger directed from the cave and vice versa in summer� than in Križna Jama and this is the reason air if temperature differences are smal , direction of flow cannot be observed along the main water air flow alternates in less than one minute� Cross- passage� Figure 3.1.5. Entrance to Križna Jama (left) and Križna Jama 2 (right). 3.1.1 Measurement location KJ-1 – temporal variability of processes at Brzice A widely accepted belief in speleology is that the contact with carbonate rock to the spring (Palm-intensity of dissolution strongly corresponds er 2000; 78)� in practice it is not as simple since to discharge� during higher discharge the dis- equilibrium is strongly influenced by CO2 con-solution rates should be greater and at lower centration, which varies in the aquifer and can discharge less intensive (Palmer 2007)� This is lead at ventilated places to CO2 outgassing and related to the kinetics of limestone/dolomite dis- consequentially to oversaturation – especially solution, which is at the first contact with soluble during low discharge� This phenomenon was ob-rock very fast (exhibits high dissolution rates) served by Palmer (2002, 2007) in McFaill’s Cave and later slows down while reaching equilibrium (New York, uSA), where the calcite saturation (dreybrodt 1988, Gabrovšek 2005)� Therefore, index (SiC) falls below 0 at high water levels and during high discharge, flow is faster and aggres- rises above 0 at low water levels� At such water sive water can deeply affect a carbonate massif� levels sinter deposition was observed� Non-linear kinetics of dissolution when the wa- According to general theoretical knowledge, ter approaches equilibrium should keep (in theo- rain-snow flow regime, and sinter deposition rate ry) the water aggressive all the way from the first measurements done by Mihevc (1997), we would 39 Case Studies - Križna Jama-Križna Jama 2 cave system expect the highest deposition rates in summer/ By far the highest sinter deposition rates occur winter (during the lowest discharge) and the in winter, when the water level is usually lower highest dissolution rates in autumn/spring (dur- (Fig� 3�1�7)� But lower water levels occur also in ing the highest discharge)� summer, when higher sinter deposition rates are absent� Further, in some summer months Temporal variation of chemical processes in the main wa- weak dissolution was detected� dissolution rates ter stream was observed at measurement location KJ-1 are extremely weak and are not stronger than (Fig. 3.1.6) located at Brzice (rapids) 10 m downstream from -0�3 µm/15 days� dissolution usually occurs the first lake. Measurement started on 14 February 2006 and in the late summer or early autumn months finished on 5 April 2009. Water flow here is considered to be and is usually absent in spring months when ful y developed turbulent flow with mean water velocities of discharge is also high� Even at exceptionally high more than 0.5 m/s. Water flow at the measurement location water level on 30 May 2006 (HFirst lake = 120 cm) was absent when the water level in the first lake fell below the dissolution rate was very weak, at only -7 cm (on average several weeks per year). We used two lime- -0�1 µm/15 days� stone tablets – one was exposed at the measurement location Weak correlation between discharge and dis- and the second was at the same time dried in the chemical solution or sinter deposition can also be seen in laboratory at the Karst Research Institute ZRC SAZU. Tab-Fig� 3�1�8, where dissolution/sinter deposition lets were switched after 15 days of exposure. Limestone tablets rates are plotted together with the height of wa-were fixed on iron screws with iron nuts and two felted inox ter and specific electrical conductivity measured washers 2 cm above the channel bed. Although we noticed a at the first lake� if we consider specific electri-little iron oxide on the limestone tablets we estimated its influ- cal conductivity as a rough approximation of ence as negligible (less than -0.1 µm/15 days). dissolved limestone/dolomite, since water is Figure 3.1.6. Ground plan of the Križna Jama – Križna Jama 2 cave system with measurement locations. 40 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.7. Dissolution and sinter deposition rates between 14 February 2006 and 5 April 2009 at measurement location KJ-1 in Križna Jama. Figure 3.1.8. Dissolution/sinter deposition rates during spring-summer 2007 at measurement location KJ-1. Discharge and specific electrical conductivity (SEC) were measured at the first lake. 41 Case Studies - Križna Jama-Križna Jama 2 cave system clean, we see practical y no correlation between has to be high enough for satisfactory flux of height of water and dissolution/sinter deposition CO2 from the water, and rates� during high water levels in March 2007 iV� some nuclei (e�g� calcite crystals) have to be (HFirst lake = 52 cm) slight sinter deposition was re-available for deposition, especial y at low corded� oversaturation (Roques 1969; 155)� The acquired data are far from what was ex- pected and we can be sure that discharge is not Periodic measurements of specific electrical the most important factor that controls the stron- conductivity (SEC) and several chemical analyses gest chemical processes� Since the strongest sinter show relatively high SEC (general y from 445 deposition rates seem to correspond to the strong and 490 μS/cm, on 27 March 2007 366 μS/cm ventilation of Križna Jama in winter months, (HFirst lake = 52 cm)) and high calcium hardness high sinter deposition rates can be related to out- of water (4�0-4�5 meqv/l)� When the water gassing of CO level is very high (for example on 30 May 2006; 2 from the water that is stimulated in winter by the inflow of outside air poor in CO HFirst lake = 120 cm), the concentration of Ca2+ fal s 2� The precipitation of calcium from the water solu- to 2�85 meqv/l and the water should become tion is a final result of several chemical reactions slightly aggressive (SiC = -0�1)� Therefore, the first (Fig� 3�1�9) that are driven by the outgassing of condition is not problematic for sinter deposition CO at measurement location KJ-1� Only at higher 2 from the water and ends with the chemi- cal deposition of CaCO and very high water levels (HFirst lake ≈> 10 cm) 3 (dreybrodt 1988)� The cause for this flux of CO does the concentration of Ca2+ seem to be too low 2 from the water is lower CO for detectable sinter deposition� 2 concentration in the air� At least four condi- tions have to be fulfilled for sinter deposition: The third condition is not problematic since measurement location KJ-1 is located at rapids� i� water has to contain a high amount of dis- At such places turbulent water flow (very high solved limestone/dolomite and has to be at or Reynolds number) is common and the ratio be-close to equilibrium with respect to calcite, tween water volume/interface water-air is the ii� concentration of CO2 in the air has to be suf- highest� interface between water body and in-ficiently low to support outgassing of CO2 terface water-air is enlarged also because of air from the water, bubbles which pass into the water at steep rapids� iii� interface between the water body and air The flux of CO2 from the water is much more reduced at poorly turbulent water flow (medium- high Reynolds number), which appears in lakes upstream from Brzice� The fourth condition (nucleation) can be a problem in the first lake, where the water flow is deep and wide, but not at Brzice, where the contact with the surface of crystals is sufficient� Therefore, deposition of calcite on already estab- lished crystal lattice is not a limiting factor� According to the highest rates of sinter deposition in winter (Fig� 3�1�7) and occasional measurement of air CO2 concentration, the strongest control can be cave air CO2 concentration� At measurement location Figure 3.1.9. Schematic presentation of reaction KJ-1, measurements of CO2 concentration sequence due to outgassing of CO2 from the water. (Fig� 3�1�10) show that short-term variations 42 Case Studies - Križna Jama-Križna Jama 2 cave system of CO2 concentration are strongly influenced passages behind them and maybe also the poorly by the direction of air flow in the cave� during ventilated Blata passage� in such meteorological winter months, outside air is entering the cave conditions outgassing of CO2 takes place all along intensively through the main entrance and the water course and can reach substantial y reduces cave air CO2 concentration at KJ-1 to high SiC at KJ-1 for high sinter deposition rates� about 350 ppm� usual y during summer months, General y speaking, substantial y high sinter the air flow is the opposite and the cave air CO2 deposition rates occur only during the days when concentration is much higher (up to 3,880 ppm)� the maximum daily temperature remains below Although the latter values can also be appropriate -2 °C� From the first condition we know that high for CO2 outgassing, the best conditions for sinter deposition rates are also influenced by outgassing of CO2 from the water are during discharge, which should be lower than 0�2 m3/s winter months� (HFirst lake ≈ 10 cm)� during favourable conditions, But in several cases even when the water level SiC should be higher than 0�7 (at such SiC sinter and cave air CO2 are low, high deposition rates deposition rates do not exceed 0�5 µm/15 days), are absent (e�g� second part of September and which is in accordance with usdowski (after October 2008)� in Fig� 3�1�11 we can see that dreybrodt 1988; 269), according to whom SiC high sinter deposition rates are strongly related should be higher than +1, but not with Palmer to intensive and/or long winter ventilation of (2007), according to whom SiC should be higher the cave and that minor autumn and spring than +0�2� Some other authors (Jacobson & ventilation is not sufficient for high sinter udowski 1975 after dreybrodt 1988; 256) did not deposition rates (the only exceptions are the recognize calcite precipitation even at SiC = +1, last values in 2009)� Therefore, substantial sinter which is probably related to the presence of other deposition rates at KJ-1 can be observed only if ions� ventilation is strong and long enough to ventilate Fig� 3�1�11 also demonstrates how impor- all of Glavni Rov, the big col apse chambers Križna tant long-lasting low temperatures are in win-Gora and Kristalna Gora, known and unknown ter for the total amount of sinter deposited at Figure 3.1.10. Cave air CO2 concentration at KJ-1 during the year. 43 Case Studies - Križna Jama-Križna Jama 2 cave system measurement location KJ-1� Although minimal high water levels erosion should also take place average daily temperatures were similar during (Gospodarič 1974; 332), since some potholes are the winters of 2006/2007 and 2007/2008, intru- developed in the present-day water channel� Such sions of atmospheric air into the entrance part of statements are based exclusively on the study of Križna Jama were much longer during the winter the morphology of the water passages of Križna 2007/2008� Such long-lasting events highly venti- Jama, which should correspond to present-day lated passages in Križna Jama and caused much processes� Contrary to these statements we were high sinter deposition that winter� during the not able to observe any important erosional dam-relatively warm winter of 2006/2007 only 7�3 % age at measurement location KJ-1, although the of sinter was deposited in comparison with the limestone tablet was placed in the middle of the much colder and longer winter of 2007/2008� water flow and high water definitely transports direction, duration and intensity of air flow in particles with diameters of up to 2 mm� dissolu-winter therefore strongly influences the amount tion rates are also surprisingly low� The highest of sinter deposited at KJ-1� dissolution rate (-0�4 µm/15 days; October 2007 Observations at several springs (Pitty 1968 and October-November 2008) was detected out after White 2006, Shuster & White 1971 after of very high water levels� Even when intensive White 2006; 145) showed two types of fluctua- and long-lasting floods occurred at Bloke pla-tions regarding hardness, SiC and CO2 concentra- teau (from 2 to 15 April 2008) and water levels in tion in water that can influence dissolution/sinter Križna Jama did not fall below HFirst lake = 20 cm deposition rates: for 13 days, we detected sinter deposition • seasonal fluctuation due to CO (0�8 µm/30 days)� All these data demonstrate that 2 production in the soil and dissolution rates are extremely low and not re- • erratic discharge-dependent fluctuation lated to the high water levels� caused by increased discharges� Since the dissolution rates are so low in Križna Jama, even the smallest 3 mm deep scallops Erratic and seasonal variations in dissolution/ could hardly have been formed even during the sinter deposition rates can be observed in Križna Holocene� Since the scalloped wal s of the first Jama (Fig� 3�1�7)� Erratic rates were already de- lake do not correspond to present-day slow-scribed as a result of intensive winter ventilation� flowing water (even at high water levels, water if we exclude such events from analysis (sinter flow is too slow for the formation of 3 cm long deposition rates higher than 0�5 µm/15 days), a scallops), such dissolutional features are inherited seasonal pattern can be seen clearly in all years� from the more distant past� decantation flutings, This seasonal pattern can be seen as low sinter which can be observed on the wall of the first lake, deposition rates during winter and spring that are nowadays always under the water level and turn into weak dissolution rates during summer covered with flowstone coating� Location (under and autumn� Seasonal fluctuation can be related the water level) and the flowstone coating are to seasonal variation of CO proofs that they are not developing with present- 2 in the cave air and in the karst massif (Fig� 3�1�10) or seasonal fluctua- day processes and that they are inherited from the tion of CO past� 2 in the soil and consequently in auto- genic recharge� To find the proper answer, further Factors which would cause higher dissolution study on water chemistry is necessary� rates are connected with ventilation (reduced Gospodarič (1974; 332), Gospodarič & Habič winter ventilation) or hydrology (lower total (1979; 59) and Slabe (1989; 91, 1992; 217) all hardness)� Closure or opening of entrances oc-state that dissolution takes place in Križna Jama curs quite often (Brodar 1949, Brodar 1966, Bro-at high water levels, when scallops are formed� At dar 1970, Spötl et al� 2005; 2467) and would lead 44 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.11. Difference between average daily outside temperature and cave temperature (~8 °C), wind direction and dissolution/sinter deposition rates between 14 February 2006 and 5 April 2009. to weaker ventilation, higher CO2 concentration measurements (1997), a sinter deposition rate in the massif and probably higher dissolution amount of 100 µm/a� Our value is 4�8 times lower rates� Lower hardness could be achieved with (20�7 µm/a), which is a result of the difference lower CO2 concentration in the soil and in the between methodologies (Fig� 2�10 in Chapter vadose zone� The latter characteristic occurred 2�2) where MEM measurements are more reliable during ice Ages since the present-day forest in absolute terms� Over 12,000 years, the sinter above Križna Jama then consisted of grassland deposition rate observed by Mihevc (1997) with clumps of trees (Šercelj 1974) due to lower would result in a 1�2 m high rimstone dam which temperatures� roughly corresponds to the actual estimated Nowadays the prevailing process at Brzice is height of the rimstone dam at Brzice downstream sinter deposition; according to Mihevc’s MEM from the first lake� 3.1.2 Measurement location KJ-2 – temporal and spatial variability of pro- cesses in the first lake Strictly speaking, it is impossible to delineate limestone tablets� Such type of measurement dissolution rates from sinter deposition rates also provides us variation of dissolution and at measurement location KJ-1, where the sinter deposition rates according to depth processes overlap at the bed of a channel and makes possible comparison between even within 15 days� Therefore we started to measurement locations KJ-1 and KJ-2 (Chapter measure in the first lake with a vertical set of 3�1�3)� According to the actual morphology 45 Case Studies - Križna Jama-Križna Jama 2 cave system of the passage we should expect net sinter periods of very intensive ventilation (Pearson deposition below HFirst lake = 0 cm and slight product moment correlation coefficient between (net) dissolution above this limit� Results sinter deposition at KJ-1 and sinter deposition represented in Fig� 3�1�12 partly confirm this on limestone tablets at HFirst lake = 2�5 cm amounts presumption� to 0�19 and decreases with height)� in zone 2 sinter deposition takes place exclusively in late Measurements at KJ-2 (Fig. 3.1.4 and 3.1.6) started on autumn, winter and spring (November-April) 17 June 2006 and finished on 5 April 2009. A vertical set during periods of medium-high water levels (up of 21 limestone tablets was instal ed on a water gauge. The to HFirst lake = 20 cm)� Quite low sinter deposition vertical distance between limestone tablets was usual y rates result in a thin layer of flowstone coating, 5 cm. Water flow was much slower in comparison with KJ-1 which can be visible on cave wal s just in the because though the discharge is equal the cross-sectional area lowest section� Higher, the coating is too thin to is much larger. During low and medium discharge water flow be visible to the naked eye� can be defined as low turbulent and subcritical. During high discharge water flow was more turbulent but not supercritical. Limestone tablets were replaced in the same way and at the same time as at measurement location KJ-1. They were fixed with brass screws, nuts and washers. We observed no colour or dissolutional changes on limestone tablets under the brass screws and washers. The results can be summarized in three vertical zones: 1 – zone of gradual lowering of sinter deposition rates downward (below HFirst lake = 0 cm), 2 – zone of gradual lowering of sinter deposition rates upward (between HFirst lake = 0 cm and HFirst lake = 20 cm) and 3 – zone without changes or with slight dissolution (above HFirst lake = 20 cm)� Periods of high sinter deposition rates in zone 1 correspond to those at measurement location KJ-1, within a few days in winter when the passage is well ventilated (Fig� 3�1�13)� Since the outgassing of CO2 occurs at the water surface the highest SiC close to the water surface of low-medium water levels is expected� Below low-medium water levels sinter deposition rates are lower� At HFirst lake = -37�5 cm the sinter deposition rate drops to only half of the one at HFirst lake = -2�5 cm� This zone of sinter deposition can be observed on cave wal s as up to 3 cm thick subaqueously deposited flowstone coating� Figure 3.1.12. Dissolution and sinter deposition Sinter deposition was observed also at KJ-2 between 17 June 2006 and 5 April 2009. in zone 2 but the rates are much lower in Results represent the sum of 69 usual y 15-day comparison with zone 1 and are not related to measurements. 46 Case Studies - Križna Jama-Križna Jama 2 cave system Zone 3 indicates almost equal weights of the scalloped wall of the first lake, where the limestone tablets before and after exposure and length of scallops is unbalanced with present-no gradual transition can be observed� The sum day hydrodynamic conditions, is inherited from of all results for the whole measurement period the past when at least the channel was narrower� in zone 3 is -0�2 µm, which indicates slight The latter explanation is possible since we know dissolution� Extremely weak dissolution rates that Križna Jama was intensively filled with in zone 3 is beside slow water flow in this area allochthonous material, which was later washed even during high discharge, another proof that away (Gospodarič 1974)� 3.1.3 Comparison of measurement locations KJ-1 and KJ-2 – important differences in sinter deposition rates between rapids and lakes Comparison between measurement locations rimstone dams underground and similar trav- KJ-1 and KJ-2 shows some differences in sinter ertine dams in superficial streams� This is also deposition rates which are the result of equal the case in Križna Jama, where more than water but different velocity of water flow that 40 lakes have been formed beyond rimstone influences the diffusion boundary layer (drey- dams� A comparison between rapids (KJ-1) brodt & Gabrovšek 2009)� Such differences in and lake (KJ-2) are represented in Fig� 3�1�13� sinter deposition rates produce well-known if we take into account only very low sinter Figure 3.1.13. Dissolution/sinter deposition rates and their cumulative values at measurement locations KJ-1 (rapids) and KJ-2 (lake) between 17 June 2006 and 5 April 2009. 47 Case Studies - Križna Jama-Križna Jama 2 cave system deposition rates (below 0�2 µm/15 days) we notice HFirst lake = -2.5 cm at measurement location KJ-2, that sinter deposition rates at KJ-1 and KJ-2 are ΔD is the amount of sinter deposited at KJ-1 and H equal or even KJ-2 slightly prevails� differences is the depth at measurement location KJ-2. appear only at higher sinter deposition rates, when sinter deposition rates at KJ-1 are general y Between HFirst lake = -2�5 cm and HFirst lake = 20 cm up to 17-times higher in comparison with KJ-2 sinter deposition rates decrease can be described and as a result rimstone dams and lakes behind with Eq� 3�1�2� them are formed� Without intensive ventilation in winter time differences between KJ-1 and KJ-2 ∆ d = ∆ cm D × − × H + (− 5 . 2 −20 ) ( 0013 . 0 0277 . 0 ) would be negligible and rimstone dams could not be formed� The mechanism for differential rate is (Equation 3.1.2), still unclear (Hammer et al� 2007; 259) since it can be related to (a) enhanced precipitation under where Δd(-2.5—20 cm) is the amount of sinter higher flow velocity because of the thinning deposited in depth between HFirst lake = -2.5 cm and of a diffusion-limiting boundary layer (Liu HFirst lake = 20 cm at measurement location KJ-2, 1996, dreybrodt 2004; 187) or (b) accelerated ΔD is the amount of sinter deposited at KJ-1 and degassing of CO2 due to agitation, pressure drop H is depth at measurement location KJ-2. and shallowing� Tab� 3�1�1 shows portions of sinter deposited at Regarding Eq� 3�1�2, Eq� 3�1�2 and the average different depths at KJ-2 in comparison with KJ-1� deposition rate 100 µm/a near KJ-1 (Mihevc The decrease of sinter deposition rates is evident 1997), we can model sinter deposition during the with depth� For all data a high Pearson product Holocene (over the last 12,000 years)� if sinter moment correlation coefficient is characteristic deposition rates were similar in this period to but fal s with depth� The latter phenomenon is present-day values, rimstone dams would be probably a result of higher measurement errors, 120 cm high, the thickest flowstone coating at which increase with lower rates� the wall of the first lake would be about 3�2 cm Regarding the values presented in Tab� 3�1�1, thick and would decrease under HFirst lake = -77 cm we can describe decreasing sinter deposition (Fig� 3�1�14)� The highest real thickness of rates with Eq� 3�1�1� flowstone coating (up to 3�5 cm) and decreasing thickness with depth is in agreement with field × 0283 . 0 H d ∆ = ∆ × 1168 . 0 × (−37 5 . −− 5 . 2 ) D e cm observations and additional confirmation that rimstone dams and flowstone coating were formed (Equation 3.1.1), during the Holocene� Nevertheless, the thickness of flowstone coating between HFirst lake = 0 cm and where Δd(-37.5--2.5 cm) is the amount of sinter HFirst lake = 25 cm does not correspond to present-deposited in depth between HFirst lake = -37.5 cm and day morphology (flowstone coating is up to Table 3.1.1. Portion of deposited sinter at different depths at KJ-2 in comparison with KJ-1 based on data obtained between 17 June 2006 and 3 May 2008. Depth at KJ-2 (cm) -7.5 -17.5 -27.5 -37.5 Portion of deposited sinter at KJ-2 regarding to KJ-1 10�0 % 6�8 % 5�1 % 4�3 % Pearson product moment correlation coefficient 0�88 0�81 0�74 0�72 between rates at KJ-1 and KJ-2 48 Case Studies - Križna Jama-Križna Jama 2 cave system several millimetres thick and not up to 17�5 mm present-day sinter deposition rates several cm as modelled), which can be a result of higher above HFirst lake = 0 cm� Figure 3.1.14. Model ed flowstone coating growth regarding Eq. 3.1.1, Eq. 3.1.2 and sinter deposition rate 100 µm/a near measurement location KJ-1 (Mihevc 1997) for the last 12,000 years. 3.1.4 Measurement locations KJ-3, KJ-4 and KJ-5 – spatial variability of pro- cesses in the water course between Kalvarija and Ponor The water course between Kalvarija and Ponor measurements of the physicochemical properties of water. is characterized by 13 lakes formed behind MEM measurements were taken at three locations between rimstone dams� The positions of the rimstone the first lake and Ponor. Some of them were already set by dams indicate that they started to grow at places Mihevc in 1994. At each place we obtained three values. with initially highly turbulent water flow, such On 20 November 2006 we extended measurements to as inclined passage floors and breakdowns� At three upstream locations, where we could get six values per such places higher sinter deposition rates are measurement location. All places are laying on rimstone dams characteristic in comparison with lakes, as in similar water flow conditions, except for the measurement previously described� With measurements at location between the seventh and eighth lakes, where the different places between Ponor and Kalvarija we rimstone dam is partly flooded. Therefore we could expect observed spatial dynamics of sinter deposition much lower sinter deposition rates due to slower and less rates downstream from the confluence at turbulent water flows. Kalvarija and endeavour to recognize basic Measurements with limestone tablets began on factors that influence the variability of rates� 16 August 2006 at KJ-4 and KJ-5. Later, on 13 January 2007, they were extended to KJ-3, which lies 4 m upstream from Geomorphic processes between Kalvarija and Ponor were KJ-1 (Fig. 3.1.6). Due to difficulties with fixing the tablets measured with a micrometer (MEM), limestone tablets and and environmental limitations they were fixed in deeper 49 Case Studies - Križna Jama-Križna Jama 2 cave system water than where the MEM measurements were taken. Due that sinter deposition rates decrease from Ponor to the development of iron oxide on iron screws at KJ-4 and toward Kalvarija� Only at the measurement KJ-5 that caused misleading dissolution (Chapter 2.2), we location between the seventh and eighth lake was started with contemporary measurements with limestone the sinter deposition rate significantly lower� This tablets fixed on stainless steel parts several centimetres beside decrease in sinter deposition rates is characteristic the older measurement locations on 18 December 2007. At for the winters 2006/2007 and 2007/2008� The measurement location KJ-3 we used inox screws, washers and Pearson product moment correlation coefficient nuts from the beginning of taking measurements. Limestone between the sinter deposition rate and the tablets were usual y changed after 30 days of exposure. distance from the entrance is significantly high Spatial measurements of physicochemical properties of even if we take into account the measurement water (SEC, T and pH) were made with a WTW Multiline location between the seventh and eighth lake, P4 at different hydrological and climatic conditions between 0�92� Without the measurement between the 15 October 2006 and 8 January 2009. seventh and eighth lake, the Pearson product moment correlation coefficient is very close to Rates and spatial variability of dissolution/ perfect correlation (-0�96)� Between the ninth sinter deposition are best seen in Fig� 3�1�15 and tenth lake only 54 % of sinter is deposited and in Fig� 3�1�16, which represent the results in comparison with measurement locations of measurements taken with a MEM� it is clear between the first lake and Ponor� Figure 3.1.15. Locations and results of MEM measurements between Kalvarija and Ponor from 30 November 1994 to 12 September 2008 (data from 1994-1997 were measured and published by Mihevc 1997). 50 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.16. Decrease in sinter deposition rates from Ponor toward Kalvarija. In equation A, we take into account the sinter deposition at the rimstone dam between the seventh and eighth lake; in equation B values from this measurement location are excluded. Another very obvious phenomenon is the con- misleading dissolution (at the end of 2007, parallel nection between sinter deposition rates and win- measurements also started with limestone tablets ter ventilation, already known from measurement fixed with inox parts)� in spite of these problems, location KJ-1 at Brzice (Chapter 3�1�1)� Since the it is clear that at all places sinter deposition rates winter of 2007/2008 was significantly colder than are influenced by strong ventilation of the cave the winter of 2006/2007, a much thicker flow- during winter (Fig� 3�1�17)� if we take into account stone coating was deposited in 2007/2008 at the limestone tablets fixed with inox, the Pearson majority of measurement locations� differences product moment correlation coefficients are are the largest farther from the entrance� in win- higher than 0�96 between KJ-3 and KJ-4 or KJ-3 ter 2006/2007 Križna Jama was so poorly ven- and KJ-5� The greatest differences occur at high tilated that sinter deposition between the third sinter deposition rates, when by far the highest and fourth lake was slightly above zero but at the rates are observed at KJ-3� Toward Kalvarija, rimstone dam between the ninth and the tenth sinter deposition rate strongly decrease� At KJ-4 lake we detected even slight dissolution (-10 µm), it fal s to 12�6 % and at KJ-5 it fal s to 7�1 % of that caused most probably during the previous sum- recorded at KJ-3� This decrease is much greater mer and early autumn months� than that observed with MEM measurements Absolute rates defined through the use of due to the much faster water flow at KJ-3 in limestone tablets do not reflect absolute rates of comparison with KJ-4 and KJ-5� sinter deposition on rimstone dams but rather the insight into the speleogenetic processes relative difference between measurement periods between Ponor and Kalvarija is also possible and measurement locations due to (a) freshly cut through spatial measurements of SEC and pH, surfaces of limestone tablets (Chapter 2�2), (b) but, due to aspects of physical access and a lack lower rates due to deeper water at KJ-4 and KJ-5 of data loggers, only at low and medium water and (c) usage of iron parts for fixation that caused levels� Such measurements are easy to take and 51 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.17. Comparison of sinter deposition and dissolution rates between KJ-3, KJ-4 and KJ-5 from 13 January 2007 to 19 March 2009. After 18 December 2007 measurements were also done with limestone tablets fixed with inox. reliable especial y in this case where we have water increases SiC and leads to sinter deposition no tributaries that can change physicochemical that was recorded with downstream lowering of properties of the water along the water course SEC� due to continuous outgassing of CO2 from (Fig� 3�1�3)� the water downstream, an increase of SiC is Measurements show that pH is increasing (up expected downstream that results also in higher to +0�31) and SEC is slightly decreasing (Tab� 3�1�2) sinter deposition rates� from Kalvarija toward Ponor throughout the year A downstream decrease of SEC makes possible at low and medium discharges� The increase in the calculation of sinter deposition rates along pH indicates a decrease in H+ concentration the cave stream� To convert the decrease of SEC and since we observe a downstream decrease of to a decrease of the total hardness of water in SEC, the downstream increase of pH can only be mg/l, Eq� 3�1�3 obtained by Krawczyk & Ford caused by outgassing of CO2 from the water and (2006 after Ford & Williams 2007; 63) that was not by dissolution� Outgassing of CO2 from the established from >2300 field analyses was used� Table 3.1.2. Amount of deposited calcite (Δm CaCO3), average thickness of deposited flowstone coating (Δd CaCO3) and average weight change of average limestone tablet (Δm) regarding discharge and spatial SEC measurements between Kalvarija and Ponor. Discharge SECKalvarija SECPonor ΔSEC Δm CaCO3 Δd CaCO3 Δm (mg; (l/s) (µS/cm) (kg) (µm) 3.000 mm2) 12 February 2007 140 456 446 10 1951 0�025 0�20 15 October 2006 9 461 452 9 113 0�001 0�01 11 October 2007 72 476 459 17 1706 0�022 0�18 18 July 2008 4 462 457 5 28 0�000 0�00 52 Case Studies - Križna Jama-Križna Jama 2 cave system into consideration that 17-times higher sinter (Equation 3.1.3), deposition rates are characteristic for rimstone dams in comparison with lakes (Chapter 3�1�3), the thickness of the flowstone coating up to where TH is total hardness in mg/L and SEC is 0�425 µm/30 days can be detectable at these rim-specific electrical conductivity in μS/cm. stone dams� Although such values can be reduced during higher water levels during measurement discharge was calculated using a stage- periods, the data (Fig� 3�1�17) at least suggest that discharge curve for a water gauge in the first rates were very low during measurement periods lake (Fig� 3�1�4)� The surface of the water channel in Tab� 3�1�2� None of the dates in Tab� 3�1�2 corre-was calculated using estimated width of passage sponds to the highest sinter deposition rates since (~7 m), average depth of water measured at the latter are quite unpredictable (they occur only 127 locations between the first lake and Otok several days per year)� during such events, which (Planina 1985) and the length of the passage with are also accompanied by the appearance of float-Eq� 3�1�4� ing rafts between Kalvarija and Ponor composed mainly of calcite (calcite-96�9 %, dolomite-2�8 %, other-0�4 %), the highest differences in SEC can (Equation 3.1.4), probably be recorded� The increase of sinter deposition rates from Kalvarija toward Ponor has clear morphological where A is cross-sectional area of water flow, evidence� Change is best seen in the thickness of W is the average width of passage, D the average flowstone coatings in lakes – it increases from depth of passage/lake and L length of a passage. less than 0�1 cm at Kalvarija to about 3�2 cm in the first lake� Similar changes downstream from Thickness of the flowstone coating can be confluences were also noticed in Pisani Rov and calculated using Eq� 3�1�5� the Blata passage (Chapters 3�1�6 and 3�1�7)� The second consequence is the decreasing length of lakes from Kalvarija toward Ponor due to the downstream increase of growth rate of rimstone dams� The initiation of rimstone dam (Equation 3.1.5), growth is definitely related to micro-location fac- tors (for example, inclined parts of passages with where Δd is the average thickness of flowstone open surface flows, position of breakdowns that coating between Kalvarija and Ponor, Q is partly block the water passage (Chapter 3�1�3)); discharge in l/s and t time in seconds. but further growth is controlled by distance from Kalvarija� Since the growth of rimstone dams Results represented in Tab� 3�1�2 are calcu- near Ponor is the most favoured, the rise of the lations for 30 days, the time used for measure- water level behind them progressively floods ments with limestone tablets� Although the the upper rimstone dams, especial y lower ones� quantity of deposited sinter at discharge of 140 l/s At such places the sinter deposition rate pro-amounts to 1,951 kg, the cross-sectional area of gressively turns from the one at the rimstone water flow is so big (29,080 m2) that the average dam toward the one in the lakes (final y, it can thickness of flowstone coating amounts to only be 17-times lower) and the growth of rimstone 0�025 µm/30 days� This is too thin a layer to be dams almost ceases� This phenomenon can be detected with limestone tablets, but if we take observed at many places above the third lake and 53 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.18. Active and ancient rimstone dams between Kalvarija and Ponor. was detected with a MEM at the rimstone dam duction of the cross-sectional profile above the between the seventh and eighth lake� Even more lakes� This phenomenon forms a negative feed-widespread are places with thicker flowstone back loop� it is especial y the case above the sec-coating on the floors, which are actual y rem- ond lake, where the roof is only about 1 m above nants of currently shallowly flooded rimstone medium water level, and in the downstream part dams (Fig� 3�1�18)� These indicate that rimstone of Pisani Rov, where the roof is less than 0�5 m dams were wider in the past and were later nar- above medium water level� At both places the sin-rowed to strips perpendicular to water channels ter growth rate is one of the highest� We can ex-where sinter deposition rates were the highest� pect that sinter deposition rates will decrease and Such flooded sinter-covered floors are now, due will be rarer in the future even without climatic to their softness, partly eroded by corrasion� As a changes (i�e� warmer winters)� The growth rate of consequence, at least 12 rimstone dams and lakes water levels due to the growth of rimstone dams behind them have already disappeared in the will decrease exponential y� As a result, middle past between Kalvarija and Ponor, especial y in water levels will never reach the cave ceiling, today’s twelfth and thirteenth lake� something that can now be observed at Nizka The growth of rimstone dams decreases the Pasaža (low passage) in the upstream part of the ventilation in Križna Jama because of the re- Blata passage� 54 Case Studies - Križna Jama-Križna Jama 2 cave system 3.1.5 Measurement locations KJ-5, KJ-6 and KJ-7 – mixing of streams from Pisani Rov and from the Blata passage at Kalvarija Kalvarija is a place of confluence of two recorded in autumn and the lowest at the end of underground streams� One comes from the winter� Blata passage and is characterized by water flow Specific electrical conductivity (SEC) of in a muddy channel formed in a horizontal and water from both passages ranges from 432 to weakly ventilated passage� The second stream 504 μS/cm at low-middle water levels� Average comes from Pisani Rov� This passage is also SEC is nearly the same (461 μS/cm for the horizontal but much better ventilated, especially Blata passage and 463 μS/cm for Pisani Rov)� in winter and summer in comparison with the The correlation between SEC and the water Blata passage� level is weak� Much better correlation was The discharge ratio between the two streams found between SEC and season (Fig� 3�1�19)� varies in time and amounts from 1:4�3 to The highest SEC was found in early summer 1:0�69� The portion of discharge from the Blata months and in early winter months� Between passage is usually higher at higher water levels� these peaks two periods with low values appear� The physicochemical properties of water at Nearly the same oscillation with almost perfect Kalvarija differ slightly with respect to measured correlation was also observed in pH, that is, T, SEC, pH and Ca2+/Mg2+ ratio� Temperatures on the other hand, on average 0�27 higher in in Pisani Rov are quite stable at 8�4 ± 0�1 °C at Pisani Rov constantly through the year� Similar low-middle water levels throughout the year� At oscillation of physicochemical parameters very high water levels, the overflow of waters in the Blata and Pisani Rov indicates similar from Bloke plateau (combined Bloščica and interaction between rock, water and at least soil Farovščica streams) can be identified (in winter atmosphere� with substantially lower temperatures)� in the despite many similarities, higher Ca/Mg ratio Blata passage, the average water temperature is (3�52) in the Blata passage indicates a higher similar but varies more with respect to season portion of limestone aquifer than in Pisani (8�4 ± 0�5 °C)� The highest temperatures are Rov (1�91)� in the Blata passage, we should also Figure 3.1.19. Year-round oscil ation of SEC and pH in Pisani Rov and in the Blata passage at Kalvarija. 55 Case Studies - Križna Jama-Križna Jama 2 cave system take into account the minor contribution of the The biggest differences between measurement underground Farovščica watercourse, which locations appear during winter months, when was proven by a tracing test (Kogovšek et al� the highest sinter deposition rates amount to 2008)� in both cases, occasional measurements 0�4 µm/30 days in the Blata passage (KJ-7) while at low-middle water levels indicate an always in Pisani Rov the sinter deposition rates amount positive SiC (from +0�29 to +0�76) and therefore to over 10 µm/30 days� in Pisani Rov (KJ-6), the slightly oversaturated waters� Nevertheless, SiC is response to winter ventilation is similar to KJ-3, usually higher in Pisani Rov than in the Blata although the sinter deposition rates at KJ-3 are passage, a result of lower pH in the Blata passage more closely related to extreme winter ventilation, (Fig� 3�1�19)� while at KJ-6 the rates are more constant� The Measurement locations KJ-5, KJ-6 and KJ-7 similar response of KJ-3 and KJ-6 is a result of were established to observe differences in the intensive winter ventilation of Jezerski Rov speleogenetic processes in Pisani Rov and the (the passage between Ponor and Kalvarija) and Blata passage and the influence of the confluence Pisani Rov, which strongly decreases cave air downstream from Kalvarija� CO2 concentration and enhances the outgassing of CO2 from the water� The Blata passage is The speleogenetic processes of the stream from Pisani much less ventilated and therefore has higher Rov, the stream from the Blata passage and the combined CO2 concentration that results in lower sinter stream (all at Kalvarija) were studied using limestone tablets deposition rates� Nevertheless, winter differences at measurement locations KJ-5, KJ-6 and KJ-7 (Fig. 3.1.6). in CO2 concentration between the upstream Measurements at KJ-5 (combined water flow downstream end of the Blata passage and Pisani Rov are too from Kalvarija) and KJ-6 (Pisani Rov) began on 16 August small (~150 ppm) to produce a much different 2006. Limestone tablets were fixed on iron screws which rate of outgassing of CO2 from the water� The caused misleading dissolution especial y at KJ-5, much less main reason for different sinter deposition so at KJ-6. On 18 December 2007, iron parts were replaced rates in winter months has to be in differential with stainless steel. Measurements at KJ-7 (Blata passage) ventilation of the whole karst massif upstream began on 15 July 2007. Limestone tablets there were fixed from both passages, which are inaccessible on stainless steel from the beginning of measurements. The for research due to upstream breakdowns� measurement interval was usual y 30 days. However, ventilation through the breakdowns and high CO2 concentration of air coming from Fig� 3�1�20 shows that the sinter deposition the breakdowns in summer indicate that the and dissolution rates at KJ-6 are nearly the same passages continue further into the karst massif� as the sinter deposition rates at KJ-7 in spring, Without the intensive ventilation of Pisani Rov, summer and autumn, which is the result of the sinter deposition rates at KJ-6 would be similar origins of water� if we exclude the sinter similar to the sinter deposition rates in the Blata deposition rates higher than 1 µm/30 days that passage or to the sinter deposition rates several occur in winter, results from KJ-6 and KJ-7 (and hundreds of metres downstream from Kalvarija� also downstream) show gradual transition from Partly different catchment areas of streams the sinter deposition during winter and spring from Pisani Rov and the Blata passage that are months to slight dissolution during summer evident from different variations of the annual and autumn months� it is interesting how temperature of water, pH, Ca/Mg ratio and a closely KJ-6 fits with KJ-7 between 18 April 2008 tracing test (Kogovšek et al� 2008) are of minor and 5 November 2008 – the rates are just 0�1- importance� 0�2 µm/30 days higher at KJ-6 (Pisani Rov) in The sinter deposition rates downstream from comparison with KJ-7 (Blata passage)� the confluence (KJ-5) are under the influence 56 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.20. Results of measurements at KJ-5, KJ-6, KJ-7 and at KJ-3 for comparison from 13 January 2007 to 27 February 2009. Presented are just results of measurements which were not significantly affected by dissolution at the contact with rusted iron screws. of mixed physicochemical properties of water passages or even slight dissolution rates� during from Pisani Rov and from the Blata passage� in high discharge it can be slightly undersaturated, such conditions, we could expect some mixing which could together with different CO2 and dissolution (Bögli 1964 after Gunn 1986) in Ca2+ concentrations lead to higher dissolution cases when waters are different with regard to downstream from the confluence� Results of CO2 and calcium concentration and are close measurements (Fig� 3�1�20) show that when to saturation� Occasional chemical analyses higher sinter deposition rates prevail at KJ-6 during low and middle discharges show that and KJ-7, the sinter deposition rates at KJ-5 water from Pisani Rov and the Blata passage is are usually between those of KJ-6 and KJ-7 but usually slightly oversaturated; they have different during slightly aggressive water at least from the CO2 concentration as is seen from different pH Blata passage (KJ-7) dissolution rates at KJ-5 are and different Ca2+ concentrations as a result of higher, which is in accordance with theoretical similar SEC (total hardness) and a different Ca/ expectations� Nevertheless, autumn downstream Mg ratio� Consequently, the combined stream increases of dissolution rates are not high and could theoretically show sinter deposition rates close to the error of measurement� The limited somewhere between those detected in both potential of mixing dissolution was already 57 Case Studies - Križna Jama-Križna Jama 2 cave system warned of by Gunn (1986; 378), who states that favour of sinter deposition� Another important mixing dissolution can be responsible for up to conclusion is that the tributary from the Blata 20 % additional dissolution, but 1-2 % is more passage significantly reduces sinter deposition usual in normal waters� The average yearly rate rates along the Pisani Rov-Jezerski Rov water at KJ-5 is, as well as at KJ-6 and KJ-7, still in course downstream from Kalvarija� 3.1.6 Measurement locations KJ-8, KJ-9 and KJ-10 – speleogenetic processes in Pisani Rov The explored water course in Pisani Rov begins from the beginning of measurement. The limestone tablets under the breakdown at the end of the trunk pas- were always under the water level. Due to the remoteness of sage� Along its underground course toward Kalva- the end part of Pisani Rov, limestone tablets were replaced rija, the main stream is fed by at least 5 springs/ after several months of exposure. Consequently, results for tributaries� Since the uppermost four tributaries the three measurement periods are available. are very similar in SEC and temperature we sup- pose that Kristalna Gora (crystal mountain) acts The results of measurements in Pisani Rov as a restriction for a stream flowing through an are presented in Fig� 3�1�21 and Tab� 3�1�3� Two unexplored passage upstream of Kristalna Gora, phenomena can be identified: (a) sinter deposition which diffluences uniform water course� rates are significantly higher in the colder part of Along the water course in Pisani Rov, we the year (Tab� 3�1�3) and (b) sinter deposition rates observe similar geomorphic phenomena as in increase from the terminal breakdown toward Jezerski Rov between Kalvarija and Brzice – a Kalvarija (Fig� 3�1�21)� High sinter deposition scalloped wall above middle water level, flowstone rates in winter and low sinter deposition rates coating on the wall under the middle water level in summer are similar to a phenomenon already and, in a longitudinal cross-section, rimstone known from Jezerski Rov (Chapter 3�1�4)� They dams with lakes behind them� Flowstone coating are related to the winter ventilation of Križna is absent just at the lowest tributary in Pisani Jama, which significantly decreases cave air CO2 Rov� Free surface flow of this tributary is not concentration in the karst massif� it is somehow longer than 10 m and ends in a sump� Tributary surprising that summer ventilation does not water has up to 21 μS/cm higher SEC and up reduce CO2 concentration in the upstream part to 0�60 lower pH in comparison with the main of Pisani Rov so much that high or even medium water course, a result of the lack of ventilation� sinter deposition rates would appear� Since the This tributary is characterized also by a generally highest cave air CO2 concentration in summer 0�5-0�7 °C lower temperature� The influence of was detected at the most NE part and the lowest this tributary on the main stream is supposed to at the end of Matjažev Rov (Matjaž’s passage), this be relatively slight since it contributes only about data suggests that the air which is coming from 16 % of water to the main stream during low- the passages behind the terminal breakdown is middle discharges� substantially enriched by CO2 from the epikarst and the vadose zone and CO2 concentration in Present-day processes in Pisani Rov were studied at three the massif is still high at least during vegetation measurement locations: KJ-8, KJ-9 and KJ-10 (Fig. 3.1.6) from season� Of great interest is a decrease in sinter 15 July 2007 to 27 December 2008. At each measurement deposition rates downstream from the terminal location we used three limestone tablets at the same time breakdown, which was recorded in summer-for higher precision. Limestone tablets were fixed with inox autumn during the first measurement period� 58 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.21. Sinter deposition rates in Pisani Rov (at KJ-8, KJ-9 and KJ-10) from 15 July 2007 to 27 December 2008. Table 3.1.3. Sinter deposition rates in Pisani Rov during three measurement periods from 15 July 2007 to 27 December 2008. KJ-8 KJ-9 KJ-10 15 July 2007-11 October 2007 0�2 0�4 0� 2 0�3 0�3 0�2 0�0 0�1 0�0 (mm) 15 July 2007-11 October 2007 1�0 1�7 0�7 1�3 1�2 0�7 -0�1 0�2 -0�1 (mm/a) AVG (mm/a) 1.1 1.0 0.0 11 October 2007-24 April 2008 8�4 8�5 7�7 49�8 47�7 47�7 113�5 111�4 111�5 (mm) 11 October 2007-24 April 2008 14�2 14�4 13�0 84�2 80�6 80�6 191�8 188�3 188�3 (mm/a) AVG (mm/a) 13.9 81.8 189.9 24 April 2008-27 december 2008 0�5 0�4 0�4 0�5 0�4 0�3 1�9 1�8 2�2 (mm) 24 April 2008-27 december 2008 0�8 0�7 0�6 0�8 0�7 0�5 3�1 2�9 3�5 (mm/a) AVG (mm/a) 0.7 0.7 3.2 59 Case Studies - Križna Jama-Križna Jama 2 cave system downstream increase of the sinter deposition The influence of the lowest tributary in Pisani rate in Pisani Rov (10�2 µm/a along 100 m Rov toward Kalvarija can also be seen from the of stream) is similar to that in Jezerski Rov spatial measurements of SEC, pH and T� From (8�5 µm/a along 100 m of stream; Chapter springs under Kristalna Gora toward Križna 3�1�4) – as a result, between KJ-8 and KJ-10 the Gora, the SEC constantly lowers due to sinter sinter deposition rate increases by 12�8 times� deposition� The only significant rise in SEC is Nevertheless, this increase in rate is not linear observed below the confluence with the left but rather curved, with a smaller increase of tributary downstream of Križna Gora� The pH sinter deposition rate close to the terminal value usually rises because of outgassing of CO2 breakdown� Further downstream the sinter from the water� The only significant fall in pH is deposition rate downstream from measurement observed at the confluence with the left tributary location KJ-10 is lower due to the left tributary downstream of Križna Gora� downstream being located about 20 m downstream from toward Kalvarija, pH is rising again� Since the KJ-10� This was observed especially during the water is close to equilibrium at springs below second measurement period, when the average Kristalna Gora, outgassing of CO2 causes the thickness of sinter at KJ-10 (112�1 µm) was 39�2 % rising of SiC, which leads to sinter deposition� higher in comparison with KJ-6 (44�6 µm)� due to higher SiC downstream, the highest Figure 3.1.22. Flowstone coating slightly above and under the water level, located about 20 m downstream from KJ-8 (photo: Alojz Troha, DLKJ). 60 Case Studies - Križna Jama-Križna Jama 2 cave system sinter deposition rates are characteristic for The wall above middle water level is covered by the downstream part of Pisani Rov before the scallops, but since the measurements were done confluence with the left tributary� below medium water level and all measurement The prevailing sinter deposition below middle locations show net sinter deposition rates, disso-water level is in agreement with morphological lution during higher water level is probable but observation� All along the water course, features not confirmed by measurements� Very interest-like rimstone dams and flowstone coating as a re- ing features in the upstream part of Pisani Rov sult of net sinter deposition can be observed� The include horizontal stripes, which are composed thickness of flowstone coating is least near the of two more than 1 mm thick flowstone coatings ending breakdown and increases downstream (Fig� 3�1�22)� They are developed about 10 cm – as observed from limestone tablets� Net sinter above middle water level� it seems that they were deposition rates are most probably absent above formed at the water level in the time higher water middle water level since scallops without flow- level and in the time of the strongest winter ven-stone coating are developed there (Fig� 3�1�22)� tilation that was followed by dissolution� 3.1.7 Measurement locations KJ-11, KJ-12, KJ-13 and KJ-14 – the influence of tributaries in the Blata passage The Blata passage is more complex from a breakdown), at KJ-12 (a periodic tributary which is thought hydrological point of view since the main water to be the underground Bloščica course according to rare course is fed by several different tributaries observations), at KJ-13 (above the siphonal tributary at a (Fig� 3�1�3), both left and right, that influence rimstone dam) and at KJ-14 (below a siphonal tributary; speleogenetic processes� The Blata passage is Fig. 3.1.6). Measurements started on 15 July 2007 and ended significantly less ventilated than Jezerski Rov on 27 December 2008. Due to the remoteness of the end part and Pisani Rov� Therefore, CO2 concentration of the Blata passage, limestone tablets were replaced once or is higher in comparison with Jezerski Rov and twice per year, at the same times as in Pisani Rov. Therefore, Pisani Rov during winter and summer ventilation results for three measurement periods are available for regimes by more than 500 ppm� The direction this timespan. At all measurement locations we used three of air flow depends on outer temperature and limestone tablets, which were fixed on inox screws. is similar to Pisani Rov – below 8 °C air flows upstream from Kalvarija and above 8 °C in the As in all measurement locations in Križna opposite direction� Jama, the highest sinter deposition rate at KJ-11 was recorded during winter months (Tab� 3�1�4)� Because of changeable micromorphology and (most This proves that although the Blata passage is probably) also changeable rates of present-day processes much less ventilated in comparison with Jezerski and relevant factors, dissolution and sinter deposition rates Rov and Pisani Rov the ventilation regime does were measured only at four typical locations. Results do not influence less ventilated passages� Nevertheless, provide us full insight into the geomorphological activity due to weaker ventilation, the sinter deposition in the Blata passage, but, nonetheless, they do give us some rate at KJ-11 is about 3�2-times lower than the information about the intensity and temporal variation of sinter deposition at the terminal breakdown in geomorphic processes at typical locations, such as, in this Pisani Rov (KJ-8; Chapter 3�1�6)� in summer, a case, confluences. Measurements were taken at KJ-11 (the slight sinter deposition rate close to the error of spring of the longest known water course under the terminal measurement was recorded� The prevailing sinter 61 Case Studies - Križna Jama-Križna Jama 2 cave system deposition corresponds to actual morphology, ment error but shows that chemical processes are since all terminal breakdown material under the very close to equilibrium and that low rates can-medium water level is covered with flowstone not lead to observable flowstone coating, if such coating� The thickness of flowstone coatings is at all exists, even within the Holocene� during hard to estimate but certainly exceeds several cm� the time of dissolution, the real dissolution rate Where the passage is slightly inclined, rimstone in the passage is up to 10 times weaker since the dams have been forming� Lower Jurassic dolomite is much more slowly At KJ-12, where the measurements were done dissoluted in comparison with standard lime- in the side passage, the clear dolomite wall with- stone tablets (Fig� 2�8 in Chapter 2�2�3)� out flowstone coating suggests that we can expect Measurement locations KJ-13 and KJ-14 are dissolution� Micro-dissolutional features are ab- separated by only about 7 meters (Fig� 3�1�6 and sent since the Lower Jurassic dolomite is heavily 3�1�23)� Their location is interesting since an fractured and grained� Results (Tab� 3�1�4) sug- underwater tributary, detected with SEC, T gest that sinter deposition in winter months is and pH measurements seems to have a strong turned to dissolution in summer months� detec- influence on the micro-morphology of the tion of the highest dissolution rates at this place present-day water channel� The upstream part in Križna Jama suggests that the water can be dif- of the water course, characterized by several cm ferent in origin and could be at least part of the thick flowstone coating, ends with about a 1 m underground Farovščica or Bloščica flow already high rimstone dam, where measurement location confirmed for the Blata passage with a tracing KJ-13 was located� Beneath the rimstone dam, a test (Kogovšek et al� 2008)� The recorded average pool with a pipe flow tributary is located� Several dissolution rate (-0�03 µm/a) is within measure- hundreds of metres downstream, the water Table 3.1.4. Sinter deposition and dissolution rates in the Blata passage measured between 15 July 2007 and 27 December 2008 during three measurement periods. KJ-11 KJ-12 KJ-13 KJ-14 15 July 2007-11 October 2007 0�1 0�1 0�2 -0�1 -0�1 0�0 0�0 0�0 0�0 0�0 0�0 0�0 (mm) 15 July 2007-11 October 2007 0�3 0�5 0�7 -0�5 -0�4 0�1 -0�2 0�2 -0�2 -0�1 -0�1 0�0 (mm/a) AVG (mm/a) 0.5 -0.3 -0.1 -0.1 11 October 2007-24 April 2008 2�3 2�2 2�6 0�5 0�6 0�6 11�7 11�5 11�0 0�3 1�2 0�4 (mm) 11 October 2007-24 April 2008 4�3 4�1 4�8 1�0 1�2 1�2 21�7 21�4 20�5 0�6 2�2 0�8 (mm/a) AVG (mm/a) 4.4 1.1 21.2 1.2 24 April 2008-27 december 2008 0�5 0�3 0�2 -0�7 -0�6 -0�4 0�9 0�8 0�2 0�0 0�0 -0�1 (mm) 24 April 2008-27 december 2008 0�8 0�4 0�3 -1�0 -0�9 -0�6 1�3 1�2 0�3 0�0 0�1 -0�1 (mm/a) AVG (mm/a) 0.5 -0.8 0.9 0.0 62 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.23. Rimstone dam between measurement locations KJ-13 and KJ-14 during low water level (photo: Alojz Troha, DLKJ). course is characterized by a scalloped wall with coating, present-day morphology of the water an absence of flowstone coating but close to the channel corresponds to present-day processes� confluence with Tršanov Rov (Tršan’s passage; Similar confluences of the main water stream see Fig� 3�1�6) flowstone coating and rimstone with tributaries that spring from sumps and dams gradually appear again due to constant downstream outgassing of CO2 from the water downstream outgassing of CO2 (seen as rising with decrease of SEC are characteristic all along pH) and a consequential increase of SiC� the main Blata passage� Regarding morphology, Once again, sinter deposition was detected due to gradual outgassing of CO2 from the water only during winter or early spring (the second along the water stream and sudden interruption measurement period; Tab� 3�1�4), while during of sinter deposition at the confluence, sinter summer and autumn (the first and third deposition rates are the highest just before the measurement periods) chemical processes are confluence with the tributaries� close to equilibrium� An important difference From a morphological point of view, the between KJ-13 and KJ-14 occurs only during rimstone dam between KJ-13 and KJ-14 has a winter and early spring months, when sinter two-stage shape (Fig� 3�1�23)� The lower part of deposition rates are 20�5-times higher at the the dam is formed as a convex massive rimstone rimstone dam in comparison with the pool, dam while on the top of this massive rimstone but is not turned to dissolution due to mixing� dam, about a 15 cm high almost vertical Although the difference in rates can be caused rimstone dam has been developed� if we take by the already discussed difference between into consideration that real sinter deposition rimstone dams and pools/lakes (Chapter 3�1�3), rates can be from 2 to 12�5-times higher than the absence of flowstone coating several metres rates measured by limestone tablets (8�3 µm/a; downstream of the confluence indicates that Fig� 2�10 in Chapter 2�2), a 15 cm high rimstone the difference is caused by the tributary with dam can be formed during or at the beginning of pipe flow, which with relatively low pH and high Holocene� Pre-Holocene genesis of the massive SEC lowers SiC� Besides slight sinter deposition part of the rimstone dam is less probable but it rates at KJ-14 that should result in thin flowstone would be very interesting if confirmed by dating� 63 Case Studies - Križna Jama-Križna Jama 2 cave system 3.1.8 Measurement locations KJ-3 and KJ2-2 (KJ-2-1) – temporal variation of speleogenetic processes in the entrance part of Križna Jama 2 Križna Jama 2 (Fig� 3�1�2 and 3�1�3) is supposed to Annually, the sinter deposition rate prevails be a hydrological and geomorphic continuation over dissolution rates at KJ2-2-1 with a net sinter of Križna Jama� This presumption is supported deposition rate of ~1�4 µm/a� during the spring, by very similar physicochemical characteristics summer and autumn months in 2008, the of the water, the short distance between them course of sinter deposition rates and transition and the similar morphology of trunk passages� to dissolution rates is similar at all compared Although the caves are separated by more than measurement locations� Nevertheless, a slight 242 m with a deep sump of over 124 m below increase of sinter deposition rates is characteristic the collapse doline, the hydraulic gradient is from the Blata passage (Križna Jama) to Križna extremely low at low-middle water levels (~10 cm Jama 2 in spring months� Since the difference of vertical difference between water levels in between KJ2-2 and KJ2-2-1 amounts constantly connecting sumps; drole 1997)� According to 0�5 µm/30 days in 2008, we can suppose that to periodic measurements of SEC, T, pH, the annual course of sinter deposition rates and Ca2+ concentration, Mg2+ concentration and a dissolution rates was very similar in 2006 and tracing test done in 2007/2008 (Kogovšek et al� 2007� Such a seasonal course as was already 2008), at least one tributary is known between observed in Križna Jama is in Križna Jama 2 not the caves that is changing the physicochemical significantly influenced by a tributary (at least properties of the water and probably also the part of the superficial Farovščica stream) between present-day speleogenetic activity of the water� Križna Jama and Križna Jama 2, confirmed by a tracing test (Kogovšek et al� 2008)� Chemical processes at the beginning of the water stream The most evident difference between of Križna Jama 2 were studied at KJ2-1 and at KJ2-2. measurement locations KJ-3 and KJ2-2 (KJ2-2-Measurement location KJ2-1 was located 100 m upstream 1) is the absence of high winter sinter deposition from measurement location KJ2-2. Hydraulic conditions at rates in Križna Jama 2� At KJ2-2-1, the highest measurement locations were influenced by a relatively large sinter deposition rate amounts to 0�6 µm/30 days, cross-sectional wetted area that caused slower and therefore while at KJ-3 it amounts to 39�9 µm/30 days� less turbulent subcritical water flow at middle water levels. A huge winter difference in sinter deposition Usual y, tablets were replaced every 30 days. Measurements rates results in annual sinter deposition rates started on 16 August 2006 and were substantial y influenced that are at KJ-3 more than 20-times higher in by iron oxide (Chapter 2.2.3). Results at measurement comparison with KJ2-2-1� This high difference in locations KJ2-1 and KJ2-2 were substantial y improved on winter deposition rates is caused by differences 18 November 2007 when synchronous measurements with in the morphology of passages and ventilation� limestone tablets fixed with inox 3 cm away from the already Probably the most important factor is the length established measurement locations started (KJ2-1-1 and of free surface flow from the confluence to the KJ2-2-1). measurement location: outgassing of CO2 from the water that influences the sinter deposition The results of measurements at measurement rates at KJ-3 takes place in Križna Jama all the locations KJ2-2, KJ2-2-1 and at KJ-3 and KJ-7 way from Kalvarija, while at KJ2-2 (and KJ2- (Križna Jama) for comparison are presented in 2-1) in Križna Jama 2, upstream outgassing Fig� 3�1�24� The highest sinter deposition rates of CO2 from the confluence is limited to only amount to 0�6 µm/30 days while the strongest 100 m� if we compare measurement locations dissolution rates amount to -0�3 µm/30 days� KJ2-1-1, located in Pritočni Sifon (inflow sump) 64 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.24. Dissolution and sinter deposition rates at measurement locations KJ2-2 and KJ2-2-1 from 16 August 2006 (18 November 2007) to 17 February 2009 . Data from KJ-3 and KJ-7 (Križna Jama) are for purposes of comparison. and KJ2-2-1, 100 m downstream, the rates are in Križna Jama 2 does not result in higher sinter practically equal (Fig� 3�1�25)� Equal rates are the deposition rates during summer months� result of the strength and regime of ventilation: As in Križna Jama, the scalloped wall prevails at KJ2-1-1 and KJ2-2-1 in Križna Jama 2, the above and, all through Križna Jama 2, also under highest CO2 concentration is reached in winter the medium water level without any flowstone months (~3,700 ppm) due to the air flow directed coating� Since net sinter deposition rate is upstream (from the cave at the entrance) while characteristic for water channels in depths of KJ2-the lowest are characteristic for summer months 1-1 and KJ2-2-1, flowstone coating is expected in (~900 ppm)� Additionally, air flow velocity is the present-day situation� much higher in Križna Jama at several places due On the contrary, flowstone coating is to several low passages, while in Križna Jama 2 completely absent at the Pritočni Sifon and water passages are always wider and higher 100 m downstream in Križna Jama 2� The latter than 5 metres� Both factors strongly decrease discrepancy between actual morphology and the outgassing of CO2 from the water and measured processes is similar to KJ-14 (0�4 µm/a) consequently lower the sinter deposition rates in the Blata passage and to some extent the in Križna Jama 2� This is also one of the reasons upstream part of Jezerski Rov in Križna Jama that lower summer cave air CO2 concentration (~0�8 µm/a at KJ-5), where flowstone coating is 65 Case Studies - Križna Jama-Križna Jama 2 cave system missing or thinner than expected� The reasons and speleogenetic features (i�e� dissolution pan/ can be as follows: kamenitze, below-sediment bevels/decantation • corrasion, flutings, below-sediment floor pits; Slabe • dissolution under the thin loamy sediment 1995; 71, Ford & Williams 2007; 329)� Film and/or by biofilm, of loamy sediment also inhibits direct calcite • discrepancy between present-day rates and precipitation� Since we observed a thin flowstone long-term (i�e� millennial) rates and/or coating on the rocky wall but it is absent on • artificial widening of entrances� the nearby loamy sediment, dissolution under the sediment seems to be important� After 30 Corrasion definitely takes place in Križna Jama days of exposure, limestone tablets were gently and Križna Jama 2, since the underground stream cleaned and dried (see Chapter 2�2�1)� With transports allochthonous sediments and even this procedure, we avoided weighing sediment produces potholes at rimstone dams upstream deposited on limestone tablets but we might also of the third lake in Križna Jama where sinter de- break or slow down dissolution, which can be position rates are lower� Corrasion rates were not caused by biofilm or long-term decay of organics measured, but since corrasion should appear also under the sediment especial y over long periods at limestone tablets and is therefore already cal- of low discharge when limestone tablets were culated in the rates, only the difference in corra- clean� sion rates could cause any differences� However, Since the annual rates strongly depend on flowstone coating was not observed at any remote meteorological conditions during winter (see locations away from corrasion and therefore the Chapter 3�1�1), long-term measurement could latter should not be the reason for the absence of reveal lower annual net sinter deposition rates in flowstone coating in Križna Jama 2� comparison with that taken into account (2008- The second possibility is feasible since we 2009)� Severe floods that did not happen during lack flowstone coating at many loamy banks� the measurement period could also decrease Enhanced dissolution under the organic net sinter deposition rates� The relevance of this sediment was suggested by Gams (1967; 51) potential reason will be clearer in coming years and is certainly responsible for some superficial since the measurements at some places continue� Figure 3.1.25. Comparison of dissolution/sinter deposition rates between KJ2-1-1 and KJ2-2-1. 66 Case Studies - Križna Jama-Križna Jama 2 cave system insight into the Holocene sinter deposition rate Jama 2, a slightly increased ventilation does not at rimstone dams with dating can also be helpful� seem to be an appropriate reason for (potential y) Before Križna Jama 2 was dug out, ventilation higher sinter deposition rates� A more probable was observed at the entrance but it was weaker reason is the widening of the entrance to Križna than in the present-day situation� Yet since we ob- Jama in the 1940s, which could have led to in-serve no direct relation of ventilation and sinter creased moderate sinter deposition rates in Križna deposition rates in the entrance part of Križna Jama and consequently also in Križna Jama 2� 3.1.9 Measurement locations KJ2-3, KJ2-4, KJ2-5 and KJ2-6 – spatial variability of processes along the main water course in Križna Jama 2 downstream from the Pritočni Sifon (inflow At all measurement locations, sinter sump) in Križna Jama 2, on average 10 m wide deposition prevails over dissolution (Fig� 3�1�26)� and 20 m high the water passage continues On average and during all three measurement 1,300 m onward to the terminal sump called periods, sinter deposition rates increased from Sifon upanja (sump of hope)� This trunk passage Pritočni Sifon to Sifon upanja (on average from is characterized by many rimstone dams that 0�6 µm/a to 2�0 µm/a)� The value at Pritočni Sifon developed on more resistant dolomite layers or corresponds to the annual sinter deposition on breakdowns� Since we were measuring sinter rate downstream from the first lake in Križna deposition at KJ2-1 (KJ2-1-1) and KJ2-2 (KJ2-2- Jama if we exclude the high sinter deposition 1), we were interested also in sinter deposition rates caused by intensive ventilation in winter rates downstream of KJ2-2� Between KJ2-3 and months� Therefore a deposition rate of 0�6 µm/a KJ2-6, only one tributary from Kaplanov Rov seems to be the background seasonal rate of net was detected (Fig� 3�1�3)� Since it is relatively sinter deposition without very intensive winter small in comparison with the main water course ventilation� The increase of sinter deposition rates at low and middle water levels (few l/s – up to downstream is best described with a polynomial 5 % of the main water course), it seems to be of degree two where R2 amounts to 0�99� Similar quite insignificant for present-day speleogenetic sinter deposition rates at KJ2-4 and at KJ2-4 are processes along the water course� at KJ2-4 probably influenced by the tributary from Kaplanov Rov� Very similar but a much Sinter deposition and dissolution rates were measured at faster increase of sinter deposition was measured four measurement locations (KJ2-3, KJ2-4, KJ2-5 and KJ2-6; in Pisani Rov (Chapter 3�1�6) and to some extent Fig. 3.1.6). Measurement location KJ2-3 was located 10 cm in Jezerski Rov between Kalvarija and Brzice beside KJ2-2 (KJ2-2-1). At all four locations, three limestone in Križna Jama (Chapter 3�1�4)� if we simplify tablets on each location were fixed with inox screws, nuts and the downstream increase of sinter deposition felted washers. All measurement locations lie in nearly equal rates with a linear function, sinter deposition hydraulic conditions – in turbulent and supercritical water rates increase by about 10�2 µm/100 m in Pisani flow. Even at low water levels, all limestone tablets stayed Rov, 8�5 µm/100 m in Jezerski Rov and only under the water. Measurements started on 11 April 2007 0�2 µm/100 m in Križna Jama 2� The downstream and finished on 18 February 2009. Due to the remoteness level of increase is definitely not caused by the of measurement locations and fragile rimstone dams along length of water flow or total hardness but rather the main water course, limestone tablets were replaced only by the huge difference in outgassing of CO2 from three times and data for three measurement periods are the water due to higher CO2 concentration in available. Križna Jama 2, although much better conditions 67 Case Studies - Križna Jama-Križna Jama 2 cave system exist for outgassing in Križna Jama 2 due to its which is a much smaller value in comparison higher gradient of water flow� with the change of 5-17 μS/cm along the 1,165 m deviation within each measurement location long water course between Kalvarija and Ponor grows from Pritočni Sifon to Sifon upanja� This in Križna Jama (Tab� 3�1�2 in Chapter 3�1�4)� The is another hint that different rates of increase downstream change of pH value is much more within each measurement period is a result of complex in Križna Jama 2 in comparison with water flow through Križna Jama 2 and a result Križna Jama since pH is decreased by sinter of temporary changeable conditions along the deposition and at the same time increased main water course� Results from the second by weaker outgassing of CO2 from the water� measurement period are interesting since we Especially in the middle part of Križna Jama 2, detected a decrease of sinter deposition rates pH is very stable� between KJ2-5 and KJ2-6 that is not related to Two longitudinal cave air CO2 measurements measurement error� Another case of downstream downstream in Križna Jama 2 during spring decrease of sinter deposition rates was between and winter (Fig� 3�1�28) show that the CO2 KJ2-3 and KJ2-4 in the third measurement concentration significantly fluctuates only near period� The reason is unknown� the entrance due to the intrusion of outside air Lower sinter deposition rates and outgassing of while at Sifon upanja cave air CO2 concentration CO2 from the water along the water stream were is nearly constant at about 2,000-2,300 ppm� Such also measured with the spatial measurement of high CO2 concentrations were rarely detected in SEC and pH (Fig� 3�1�27)� A typical change in Križna Jama� SEC due to deposition over the 1,300 m long The morphological result of sinter deposi- water course is 2-4 μS/cm in Križna Jama 2, tion recorded with limestone tablets should Figure 3.1.26. Sinter deposition rates in Križna Jama 2 from Pritočni Sifon to Sifon Upanja during three measurement periods and on average. 68 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.27. Change of pH and SEC from Pritočni Sifon to Sifon Upanja in Križna Jama 2 at different water levels. be flowstone coating and rimstone dams� the dissolution under the loamy sediment during the Holocene according to sinter de- that covers the water channel in lakes but not position rates from 7 to 25 mm thick flow- at rimstone dams and cascades where mea-stone coating should be deposited� in spite surements with limestone tablets took place� of this, flowstone coating is absent all along At waterfal s and rapids (Fig� 3�1�29) we the water stream� The wal s are scalloped all can observe the development of rimstone along the water course, which, on the con- dams that are due to lower rates much more trary with our measurements, indicates dis- fragile (and seem also to be thinner) in solution or inherited dissolutional morphol- comparison with Križna Jama� Their fragility ogy together with an absence of a prevailing decreases from Pritočni Sifon toward Sifon process in present-day conditions� Reasons upanja, which corresponds to the measured for this were already discussed in Chapter downstream increase of sinter deposition 3�1�8 and the most appropriate seems to be rates (Fig� 3�1�26)� Figure 3.1.28. Change of CO2 from Pritočni Sifon to Sifon Upanja in Križna Jama 2. 69 Case Studies - Križna Jama-Križna Jama 2 cave system Recent morphology of many candle- which results in a club-like stalagmite like stalagmites close to the medium water morphology� Some such stalagmites are level indicates dissolution after initiation of growing at the ~1 cm high rocky pedestal stalagmite growth, especial y close to the Sifon surrounded by the scalloped surface which upanja (Fig� 3�1�30)� For such morphology indicates parallel growth of stalagmites and of stalagmites, a uniform supply of fed dissolution by water flow that already removed water with uniform solute concentration is 1 cm of limestone� This recent morphology characteristic (Ford & Williams 2007; 285)� suggests that during higher discharge water Growth was probably constant from the can be slightly aggressive, especial y in the beginning and stalagmites are also growing downstream passages of Križna Jama 2, but in present-day conditions� it is interesting such dissolution rates are overwhelmed by that they are partly dissolved in the lower part sinter deposition rates below middle water where growth rates are much lower or absent levels where measurements with limestone in comparison with the top of stalagmites, tablets are situated� Figure 3.1.29. Rimstone dam and cascades covered by several cm thick sinter deposits between KJ2-5 and KJ2-6 during middle discharge (photo: Matej Kržič, DLKJ). 70 Case Studies - Križna Jama-Križna Jama 2 cave system Figure 3.1.30. Partly dissoluted club-like stalagmites with up to 1 cm high limestone rocky base 0.3 m above medium water level close to Sifon Upanja. Rocky bases formed in dolomite (black coating) are smal er due to slower solubility of Lower-Middle Jurassic dolomite (photo: Alojz Troha, DLKJ). 71 Case Studies - Križna Jama-Križna Jama 2 cave system 3.1.10 Conclusion The Križna Jama-Križna Jama 2 cave system is Along the water course, outgassing of CO2 one of the best examples of a horizontal cave from the water occurs that raises SiC and there-speleogenesis in the epiphreatic zone� Although fore increases sinter deposition rates downstream the system was at least partly under the during middle and low discharge� downstream influence of the allogenic recharge of Bloščica increase is the highest during the coldest winter and Farovščica, which have catchment areas on days (daily temperature remains below ~-2 °C) the Bloke plateau, nowadays tracing tests and when air flow is the strongest and long-lasting� physicochemical characteristics of the water downstream increase is characteristic for lakes indicate the dominance of diffuse autogenic and for rapids but it is more expressed at rapids� recharge from the area above and near the High downstream increase of sinter deposition cave system� Consequently, stream water has rates is terminated by tributaries� The high- high total hardness and is in equilibrium with est deposition rates are therefore characteristic higher CO2 pressure than is characteristic for for the downstream part of Pisani Rov (Križna the outside atmosphere� When such water enters Gora and Kalvarija) and the downstream end of a well ventilated cave system, outgassing of CO2 Jezerski Rov (between the first lake and Ponor) from the water leads to oversaturation with and can amount to over 75 µm/a� in shorter respect to calcite and calcite precipitation occurs� periods, sinter deposition rates can amount to From the morphological point of view, formation 17 µm/15 days� daily rates are thought to be of flowstone coating in nearly stagnant and much higher but they were not measured since rimstone dams in fast flowing water is possible� intensive deposition rates are highly unpredict- The most evident pattern in chemical processes able� Where ventilation is weaker (the Blata is seasonally driven transition of sinter deposi- passage and Križna Jama 2) ventilation-driven tion in winter and spring months and dissolution winter sinter deposition rates are much lower in summer and autumn months, which was ob- or absent� The morphological result of intensive served in the main trunk passages of Križna Jama winter ventilation is the faster growth of rim-under the medium water level� The seasonal peak stone dams in comparison with flowstone coat-of sinter deposition rates amounts to more than ing in the lakes (17:1), and the faster growth of 0�6 µm/30 days, while the strongest dissolution downstream rimstone dams that causes flooding rates amounts to up to as much as -0�3 µm/30 days of upper ones, a vast decrease of sinter deposi- (Fig� 3�1�24)� Spatial differences from upstream tion rates at flooded rimstone dams and the terminal breakdown in Križna Jama to Pritočni lengthening of lakes� The gradual rise of water Sifon (inflow sump) in Križna Jama 2 are insig- level reduces the aerated cross-sectional profile nificant� differences between lakes and rapids are of passages and consequently results in a nega-also negligible� Over the year, sinter deposition tive feedback loop since less intensive ventilation rate prevails over dissolution� Over the year, slight reduces sinter deposition rates� Since gradually dissolution prevails only at places reached by high weaker sinter deposition rates are expected the water levels and at some tributaries that emerge roof will never be reached by medium or at least from passages with pipe flow and are therefore low water levels� not ventilated� Seasonal variations can be driven Present-day climatic changes indicate higher by intensive winter ventilation of Križna Jama or temperatures, especially during winter time� if by vegetation and consequential seasonal varia- the same trend continues, we can expect lower tion in soil CO2 production� sinter deposition rates, as was already recorded 72 Case Studies - Križna Jama-Križna Jama 2 cave system in the winter of 2006/2007 (contrary to the much important changes at the Holocene-Pleistocene colder winter of 2007/2008; Prelovšek 2007)� transition are scallops and other dissolutional From 1994 (Mihevc 1997) to 2009, the variation features, which are numerous on the walls of of rates during several winters do not show any the Križna Jama-Križna Jama 2 cave system but important trend of sinter deposition decrease but at some places (e�g� in the first lake) do not cor-longer observation of sinter deposition rates will respond at least to present-day hydrodynamic be helpful to evaluate the influence of climatic conditions� They could have been formed during changes and the necessary response from Križna the last (Würmian) ice Age, when the snow line Jama’s tourist management (Prelovšek 2012)� at nearby Mt� Snežnik was between 1,200 and Along the main water courses in the Križna 1,300 m a�s�l� (Šifrer 1959)� The reason for strong-Jama-Križna Jama 2 cave system, dissolutional er dissolution rates during ice Ages are related and depositional features can be observed� Rim- to lower annual temperatures that reduced the stone dams and flowstone coating on the cave supply of CO2 from the soil (instead of the pre-wall suit present-day processes at least in Križna sent-day forest above the cave system Križna Jama� The thickness of rimstone dams and flow- jama-Križna jama 2 we can expect microter-stone coating equals measured sinter deposition mic vegetation (grassland with clumps of trees; rates over ten thousand years, which limits sin- Šercelj 1974), for which lower production of CO2 ter deposition to the Holocene � in Križna Jama, is expected�), lowers total hardness of water, low-the discrepancy between measured present-day ers the possibility for outgassing of CO2 from the sinter deposition rates (from 0�6 to 2 µm/a), water due to lower water CO2 concentration and which should result in 7-25 mm thick flowstone consequently at least strongly reduced possibility coating during the Holocene, and the absence for sinter deposition� Nevertheless, closure of the of flowstone coating is surprising and requires main entrance to Križna Jama due to breakdown additional study� The sinter deposition rate at (which is common in such climatic conditions) one measurement location in the Blata passage or changes in the catchment area (which already (KJ-13) indicates that (low) sinter deposition occurred in the cave system) would have similar rates could also be related to the pre-Holocene, results; that is, lower sinter deposition rates or although this is less probable� The main proof for even dissolution� 73 74 3.2 LEKINKA CAVE Lekinka cave (Reg� No� 1867) is a 1,032 m long karstological and speleological research in the subhorizontal cave situated at the NE edge of Postojna basin and its surroundings� Lekinka the Postojna basin about 1 km NW of the Pivka cave is the subject of only one comprehensive ponor� it is one of the several stream caves study, by Gospodarič & Habič (1966), in (e�g� Postojnska Jama (Postojna cave), Predjama, which basic geological, geomorphological and Osojca, Markov Spodmol) at the contact karst hydrological observations were made� Recently, (Mihevc 1991) that developed at the transition the influence of water CO2 on longitudinal of Eocene siliciclastic flysch rocks to Cretaceous decrease of dissolution rates and morphology limestone� The speleogenesis of big cave systems was made by Covington et al� (2012)� like that of Postojna (Chapter 3�4) is generally complex, involving many long-lasting phases, but Geological and geomorphological in the case of Lekinka cave it seems to be more characteristics simple and easier to study in short measurement The catchment area of Črni Potok (black stream), intervals (Chapter 2�2�2)� which sinks into Lekinka cave, extends on Contrary to the Postojna cave system that has the Pleistocene accumulation terrace of Pivka a long and rich research history, Lekinka cave has and Nanoščica� Fluvial deposits of weathered rarely been the focus of speleological research� siliciclastic Eocene flysch are several metres The first description of Lekinka is from the time thick and Črni Potok cuts part of its channel of A� Martel (1894; 442 after Gospodarič & Habič into underlying flysch rocks for several tens of 1966; 13)� Although the cave is easily accessible meters before contact with limestone (Fig� 3�2�1)� even during middle water levels, relatively Contact between Eocene flysch and limestone is simple for exploration and close to the touristic located 50 m before Črni Potok disappears into Postojna cave, the first survey was done by the Lekinka cave� This 50 m long watercourse lies cave club Anthron at the end of 19th century� at the regionally important thrust fault which At that time, 350 m of entrance passages were is responsible for steep contact of Eocene flysch mapped� A more detailed and longer survey was with Cretaceous limestone� done around 1926, when 387 m of underground All known passages of Lekinka cave are passages were explored by italian cavers� Finally, developed in Senonian limestone, which is the entire currently known cave was surveyed generally inclined 70-90° SW� Toward the by Gospodarič, Habič and Kenda to the Končni northeast, the inclination of strata decreases Sifon (terminal sump) around 1966� toward the Postojna anticline, which has its axis The speleological research into Lekinka cave in a NW-SE line and extends over the Postojna is even sparser than the survey of the cave� Gams cave system� The thickness of strata depends on (1966a), Michler & Hribar (1959) and Melik age – lower (older) Senonian limestone is thick- (1955) did not pay any attention to Lekinka, bedded or even non-stratified while the upper although they were concerned a great deal with (younger) is developed as stratified limestone 75 Case Studies - Lekinka cave with a thickness of strata about 1 m (Gospodarič bedding planes� This is reflected in the roughly & Habič 1966)� All Senonian limestone contains rectangular plan of Lekinka cave (see Fig� 4�2�5)� very small amounts of impurities� due to the deeper into the cave, the absence of bedding vicinity of thrusting, Senonian limestone is well planes forced passage development along faults fractured but not severely crushed in the Lekinka and cracks with a less expressive geometric cave� interbed movements at bedding planes are pattern� unknown water-filled passages between numerous (Gospodarič & Habič 1966)� Končni Sifon in Lekinka and Otoška Jama are All these geological characteristics are formed in Turonian strata, which are developed expressed in general cave morphology� Since as thick-bedded limestone with rare bedding the limestone is not crushed, breakdown planes (Šebela 1998)� Rare bedding planes can chambers are absent� in the entrance part of result in a lower possibility of the development of a cave with well-expressed bedding planes, free surface flow, and, therefore, the development passages developed along tectonically deformed of sumps� Figure 3.2.1. General geological, hydrological and speleological map of the karst massif including Lekinka cave and its superficial catchment area (source of geological data: Buser et al. 1976). 76 Case Studies - Lekinka cave Contact karst at the NE edge of Postojna Gospodarič and Habič (1966) recognized basin is subject to long-term term geomorphic Lekinka as a young ponor cave where dissolution evolution, where speleogenesis of epiphreatic still takes place� This statement is based on (a) passages began at least 530 ka ago (Zupan Hajna chemical analyses of water, which showed an et al� 2007)� Such a long geomorphic evolution increase of total solute load from the entrance resulted in large and extensive cave systems, toward inner parts of the cave, (b) on general while superficial contact karst is morphologically geomorphic evolution of terraces before ponors relatively poorly developed� For instance, only one and (c) on the “freshness” of features on the cave blind valley is developed along NE contact (the wall� On the other hand, Gospodarič and Habič fossil blind valley Risovec), while all other rivers (1966; 17) were surprised at the low increase in (Pivka) and streams (Črni Potok, Osojca) have not solute load along the water course – therefore developed any blind valley at their present ponor they also state that present-day dissolution is sites (Mihevc 1991)� Active and abundant ponor relatively weak or “some unknown chemical caves are not dispersed all along the NE edge processes take place in Lekinka, which causes of Postojna basin, rather they are concentrated the increase or decrease of solute load along the between the entrance to Postojna cave and the underground water course”� They concluded that fossil blind valley Risovec (Fig� 3�2�1); this is at the initiation of Lekinka’s first passages started only 30 % of the whole of the NE contact between during the interglacial period Riss-Würm and flysch rocks and limestone in the Postojna basin� that the formation of three wall notches found Behind this 1�9 km long contact, all known in the entrance parts of Lekinka correspond to passages of the Postojna and Lekinka caves are three young terraces in Lekinka’s catchment located� This characteristic shows that only this area� part of contact was under the long-term influence of sinking streams which flow underground Hydrological characteristics toward the NE, that is toward Planinska Jama The catchment area of Črni Potok (1�05 km2) (Planina cave)� On a smaller scale, two locations extends mainly over the Pleistocene can be highlighted from this 1�9 km long contact: accumulation terrace of Nanoščica (and Pivka; (a) the area near Postojnska Jama and (b) the area Fig� 3�2�1) between 510�5 m (the altitude of the of the blind valley Risovec� On the surface, these ponor) and 546 m� The highest, though a much two sinking points are divided by the 40 m high smaller portion, of the catchment area (~27 %) erosion terrace of Veliki Otok (545 m a�s�l�)� in lies on the slope of an erosion terrace composed the vicinity of large ponor sites, much smaller of deeply weathered flysch rocks� The very low caves are located at altitudes between 511 m a�s�l� mean inclination of the catchment area (~1º) (Lekinka cave) and 549 m a�s�l� The morphology hinders runoff and especially in marshy areas of these passages is much different from that of the outflow of brownish water rich in humic the the large passages of Postojna cave system (i�e� acids is common� As a result of low inclination, width-height ratio of passages, presence of wall soils in the catchment area are mainly brown notches, combined vadose-phreatic morphology)� eutric epigleys and hypogleys (Šporar et al�)� From their morphology one can conclude that Soil contains some cations (mainly Ca2+) due to they were formed in conditions similar to those weathered siliciclastic flysch rocks with a higher of the present-day in Lekinka cave� This finding portion of calcite cement but at some places basic is contradictory to some baseless statements cations were already washed out and more acidic (Brodar 1949; 99) that some of these narrow caves soil can be expected� As a result runoff is poor (e�g� Betalov Spodmol) were formed as branches in dissolved calcite and rich with humic acids� of large rivers (i�e� Pivka or Nanoščica)� SEC measurements show that values are mostly 77 Case Studies - Lekinka cave between 150 and 200 μS/cm� At high discharge, conduct all the water without a significant rise SEC can even be below 100 μS/cm, while at low in the water level� in Lekinka cave, the water discharge it can rise above 400 μS/cm� level significantly rises due to backflooding from The discharge of Črni Potok at the sink was the side of the high Pivka River in Otoška Jama� calculated using a water gauge 75 m from the in the latter, oscillations of more than 10 m entrance (measurement location L-1 in Fig� 3�2�4) higher than the usual water levels (~505 m) are and the stage-discharge curve set by several common during a year and can flood the water discharge measurements using the salt dilution gauging station at measurement location L-1 method� Mean discharge is estimated at 40 l/s� At (~509�5 m)� At even higher water levels, when the very low water levels, less than 10 l/s is drained Pivka with the Nanoščica are flooding in front from the catchment area and at such a level all of Postojnska Jama at an elevation of more than the water disappears into the swallow holes at 518-519 m, the waters of Nanoščica overflow its the flysch-limestone contact 50 m from the cave’s banks above Lekinka’s catchment area and cause entrance� during such an occurrence, water flow extensive floods in front of Lekinka� At the same in the entrance part of the cave is absent but time, the outflow of Črni Potok is blocked by further into the cave some water is contributed by the underground Pivka River� Such a situation tributaries� discharge of more than 1 m3/s occurs happened on 12 december 2008 (Fig� 3�2�2)� about once per year� At such and even much higher during its 1,032 m long underground course water levels, Lekinka’s passages are big enough to through Lekinka, Črni Potok descends from Figure 3.2.2. Flood in front of Lekinka (the ponor is located at the bottom left of the photo about 6 m under the water level), when the Nanoščica River rose over its banks on 12 December 2008 (photo: Mitja Prelovšek). 78 Case Studies - Lekinka cave 510�5 m to 505�5 m (Gospodarič & Habič 1966)� in Lekinka cave, the main water course of Črni Accordingly, the gradient amounts to 0�48 %, Potok is fed by several underground tributaries which is less than the underground Pivka River (Fig� 3�2�3)� At medium water levels, seven from the ponor to the first sump in Postojnska significant tributaries can be visible because of Jama (0�54 %) and the underground Pivka River their location above the water level� The exact in Planinska Jama (0�58 %; Hribar & Michler location of one underwater tributary downstream 1959)� Although the water flows perpendicular from Stranski Podor (side breakdown) was never to Senonian strata, the general deviation from defined but was detected from SEC, temperature the shortest connection with Otoška Jama is and pH measurements� Accordingly, eight quite low (27° toward the south, this is upstream tributaries were identified along the 790 m to the underground Pivka River in Otoška Jama; underground water course of Črni Potok� On the Fig� 3�2�1)� This means that the underground basis of high SEC (266-487 μS/cm) at low-middle Črni Potok is taking nearly the shortest direc- discharge and relatively constant temperatures tion to the confluence with the underground of tributary water (7�8-11�4 °C) we suppose that Pivka River and that the water flow through Le- this is mostly autogenic water as a result of kinka was always directed to Otoška Jama� On a primary infiltration in the vicinity of the cave� At smaller scale, deviations from a direct connec- medium water levels (HL-1 ≈ 5 cm), the highest tion to the underground Pivka River up to 160° portion is contributed by the fifth tributary (28 % are possible� of the water that sinks at the ponor or <18 % of in Otoška Jama, Črni Potok flows into the the entire water flow at Končni Sifon during low-underground Pivka River� The confluence was middle discharge)� The whole of the contribution first recognized by Michler & Hribar (1959) of tributaries at Končni Sifon is estimated to be when they measured water temperatures along at least 40 %� At higher water levels, the situation the underground Pivka River� The caves were was never observed due to flooding� At low water never connected due to small and branching levels, the contribution of tributaries can be up passages, which present a problem for cave divers to 100 % since Črni Potok sinks 50 m before but not a significant hydrological barrier for the Lekinka cave and was not detected in the cave at underground flow of Črni Potok� these lower levels� Figure 3.2.3. Hydrological network of the Lekinka cave regarding visual observations, SEC, temperature and pH measurements at medium water level (HL-1 ≈ 5 cm) on 13 February 2008. 79 Case Studies - Lekinka cave Meteorological characteristics Air flow can be felt throughout the cave� At the ponor of Črni Potok are two entrances, The intensity and direction depends on the which are connected through a short sump; difference between outside air temperature and about 3 m above the lower entrance, the higher air temperature in the cave (~8 °C)� Nonetheless, dry one is located, which is flooded only when water flow can cool down or warm up the cave by the Nanoščica and Pivka Rivers are exceptionally several degrees and therefore slightly influence high� the direction and intensity of ventilation� Since the whole trunk passage of Lekinka is When the outside temperature exceeds the very well ventilated, especially in summer and cave temperature, air flows from the passage winter months, a second entrance or connec- close to Končni Sifon toward Ponor� When the tion with the ventilated Otoška Jama is obvious� temperature difference is reversed, air flows Regarding higher cave air CO2 concentration in the opposite direction� if the temperature is during summer, most probable is a connection lower than 0 °C, freezing of the entrance part with Otoška Jama as was already proposed by is common and mechanical weathering can be Gospodarič & Habič (1966)� observed� 3.2.1 Measurement location L-1 – temporal variability of dissolution rates 75 m from the ponor Since Lekinka cave is a typical stream cave with Gunn 1986; 382), who has written that “further a catchment area in an accumulation terrace work is needed in order to evaluate whether and exhibits low solute load at the entrance, reliable measurements over shorter time scales we should expect relatively high dissolution are possible”� He advised the use of a micrometer rates – at least in the entrance part of the cave� or limestone tablets� High dissolution rates in a similar environment were confirmed in other karst areas (droppa Measurements of temporal variation in dissolution rates after Gams 1985; 368) and were anticipated in began on 25 September 2006 and finished on 5 April 2009. Lekinka by Gospodarič & Habič (1966)� However, Measurement location L-1 was located 75 m downstream mean dissolution rates calculated from water from Ponor and about 7 m downstream from the first left hardness were surprising – the dissolution rates tributary (Fig. 3.2.5). The water flow was always turbulent seemed to be lower than expected (Gospodarič with mean water velocities about 0.5 m/s. At very low water & Habič 1966)� Contrary to their findings, we levels (HL-1 = -5 cm), water flow was absent. To obtain insight measured by far the highest dissolution rates into the vertical variety of dissolution rates, 11 limestone in the dinaric Karst (Chapter 2�2�2)� The most tablets were exposed on a vertical water gauge. In this chapter probable reason for the low dissolution rates we use only the average value of the lower two limestone measured by Gospodarič and Habič (1966) was tablets at HL-1 = -7.5 cm and HL-1 = -2.5 cm, since they were the low discharge during which the cave was both under the water level during low-medium water levels. accessed and the water analysed� To confirm this Limestone tablets were fixed on inox screws, nuts and felted idea and to acquire deeper insight into seasonal washers and weighed in 15-day intervals on the same days variations in dissolution rates, precise short-term as in Križna Jama (Chapter 3.1). Since Črni Potok transports measurements with limestone tablets was begun a small quantity of bed and suspended load, corrasion was in the autumn of 2006� Short-term measurements expected, especial y on the lowest two limestone tablets during had been proposed by Trudgill (1977; 256 after higher water levels. 80 Case Studies - Lekinka cave Results from measurement location L-1 are presented in Fig� 3�2�6� As expected, the course of dissolution rates follows the course of the rain-snow discharge regime, which is typical for the central part of Slovenia� High dissolution rates were detected usual y at higher discharge characteristic of autumn and spring� Low discharges are characteristic especial y for summer months with less precipitation and high evapotranspiration� dissolution rates during winter depend on snow retention that can be characteristic for at least two 15-day periods (winters 2007/2008 and 2008/2009) or absent during a warm winter (2006/2007; compare with sinter deposition rates in Chapter 3�1 in Fig� 3�1�11)� Since a decrease of dissolution rates is of minor importance in winter, one maximum and one minimum in dissolution rates can be recognized from a best-fit polynomial trend line� The strongest dissolution rate amounts to -9 µm/15 days and is not related to the highest Figure 3.2.4. Measurement location L-1, used water level, while during very low water levels also as water gauge. The photo was taken at a very low (sinter) deposition rates can be expected very low water level (HL-1 = -5 cm) when only (0�2 µm/15 days)� Even during low water levels the lowest limestone tablet was under the water (H (photo: Mitja Prelovšek). L-1 ≈ 0 cm), when discharge amounts to Figure 3.2.5. Plan of Lekinka cave with measurement locations. 81 Case Studies - Lekinka cave ~7 l/s, slight dissolution rates between 0�0 and different degrees of aggressiveness of water dur- -0�7 µm/15 days can be expected� At mean ing flood pulse, the highest dissolution rates are discharge (40 l/s; HL-1 = 5 cm), the average expected during intensive precipitation (the proxy dissolution rates amount to -1�4 µm/15 days� for this can be maximum water level) and during Results obtained at the two lowest limestone long exposure to stream water (the proxy for this tablets at L-1 provide us important information can be total amount of precipitation during 15-day about changeable annual dissolution rates periods)� Fig� 3�2�6 demonstrates that high water (Fig� 3�2�6), which can be represented as a levels are not at all responsible for the highest dis-sequence of 12-month moving averages� solution rates� As a result, the Pearson product mo-According to a 12-month moving annual ment correlation factor between dissolution rates total, the minimum annual dissolution rate of and maximum height of water is low -0�37, espe- -35�6 µm/a and maximum annual dissolution cial y due to the highest recorded water level dur-rate of -78�1 µm/a was obtained� The difference ing the measurement period (HL- 1 = 730 cm), the between these two values demonstrates a strong result of an exceptional overflow of the Nanoščica� dependency of annual dissolution rates on Without this event, the correlation is much bet-precipitation during the year� Nevertheless, the ter (-0�56; Fig� 3�2�7) but still lower due to several average annual dissolution rate of -61�1 µm/a is flush floods� The limiting factor for such events is at least a relatively good approximation of the the exposure of limestone tablets to stream wa-magnitude of annual dissolution rates� ter� Consequently, the highest dissolution rates Since the dissolution rate during 15 days of were detected at medium water levels (from exposure depends on two factors, namely (a) ag- HL-1 ≈ 20 cm to HL-1 ≈ 50 cm)� This is confirmed gressiveness of water and (b) time of exposure to by a significantly higher Pearson product moment Figure 3.2.6. Average dissolution rates at the lowest two limestone tablets and their 12-month moving average between 25 September 2006 and 5 April 2009 at measurement location L-1. 82 Case Studies - Lekinka cave correlation factor between dissolution rates and Some researchers (e�g� Bray 1977) pay special at-total amount of precipitation (-0�74; Fig� 3�2�7), tention to the decay of organic matter, which can, which, partly beside intensive precipitation, in- with decomposition of organic matter to CO2 and cludes also medium but long-lasting water levels� organic acids, form complexes with Ca2+ ions (the in this case, summer months were excluded from latter reduces the activity of Ca2+ ions and there-calculation since evapotranspiration significantly fore influences equilibrium; Roques 1969; 144) reduces runoff� High positive correlation between and consequently enhance dissolution rates� Ac-dissolution rates and discharges (as a function of cording to Butturini & Sabater (2000), the highest effective precipitation) was also confirmed by oth- dissolved organic carbon, which can be a proxy er researchers (drew 1974 after Gunn 1986; 385, for the concentration of humic acids, are observed Gunn 1981b after Gunn 1986; 385)� during flood events and in autumn and winter Equations from Fig� 3�2�7 can also be used for months� The longer the exposure to aggressive wa-the evaluation of a seasonal effect if predicted and ter, the higher the dissolution rates are expected to actual rates are compared (Fig� 3�2�8)� Besides sea- be within 15 days� Our results (Fig� 3�2�8) demon-sonality as a result of the rain-snow discharge re- strate that seasonality, which is not the result of the gime, other types of seasonality can be expected� rain-snow discharge regime, is not a causal factor� Since the soil’s CO2 concentration and respiration Predicted low dissolution rates are stronger than in the water channel are strongly related to micro- actual ones but this is due to the overestimation bial activity, which is due to higher temperatures of dissolution rates using calculated equations in summer, higher soil and water CO2 concentra- (Fig� 3�2�7) and appears all through the year� More tions (Atkinson 1977 after Gunn 1986; 373, Spötl intensive actual than predicted dissolution rates et al� 2005; 2458) and higher aggressiveness of wa- are characteristic for autumn and spring months, ter can be expected during summer months� Some which can be attributed to underestimated dissolu-authors (e�g� Sweeting 1972; 219 and 226) attest to tion rates when the latter are stronger� Lack of sea-quite the contrary – aggressiveness of water should sonality also neglects the influence of water tembe higher in winter due to lower temperatures of perature, which was predicted by Corbel2 (1959 water, which enhances higher solubility of CO2� after White 1986; 261), Moore3 (1964 after White Figure 3.2.7. Correlation between dissolution rate and (a) maximum height of water during 15 days and (b) total amount of precipitation during 15 days (source of data: Slovene En- vironmental Agency). An exception- al y high water level (HL-1 = 730 cm) is omitted from both calculations due to the specific character of the event (overflow of the Nanoščica) and data for summer months in case of corre- lation between dissolution rates and total amount of precipitation. 2 Higher aggressiveness is expected in winter due to higher solubility of CO2 in cold water. 3 Higher aggressiveness is expected in summer since the biological production of CO2 is the highest in warm months. 83 Case Studies - Lekinka cave 1986; 261) and observed by Gams (1966b; 13) on was often a challenge for geomorphologists and bare rock surfaces or in superficial streams (1966b; a source of many discussions� The general y 35-37; in the latter case, differences in hardness accepted belief is that corrasion plays a minor along the watercourse are extremely slight and can role at “normal” water levels but can be a strong therefore be attributed to errors)� This does not speleogenetic factor at high water levels� during mean that these factors do not influence dissolu- floods both accelerate but corrasion can exceed tion rates but that their seasonality is not expressed dissolution (Newson 1971)� Nevertheless, a strict or is of limited significance� distinction between them is not possible, since Caves develop under a variety of processes, dissolution of limestone is usual y incomplete among which dissolution and corrasion are and the remnants of dissolution (i�e� big crystals) usual y highlighted� delineation between them are often torn away by the force of flowing water Figure 3.2.8. Difference between predicted and actual dissolution rates with regard to the comparison between maximum height of water and total amount of precipitation. After 1 June 2008, data for amount of precipitation are not available. 84 Case Studies - Lekinka cave (Zupan Hajna 2003) with or without bed load or 4 m high meander at L-1 could be developed in suspended load� in the case of Lekinka cave, high approximately 65,000 years� This is twice as fast water transports a small amount of siliciclastic as suggested by Habič and Gospodarič (1966), bed load but a lot of suspended load� The biggest who state that the development of Lekinka began and the most abrasive sediment moves close to during the Würm-Riss interglacial (114,000-the bottom of the channel but this is not reflected 130,000 years BP)� in the case of lower amounts in stronger rates at the lowest limestone tablet – a of precipitation during the Würmian ice Age, tablet that is situated at HL-1 = -7�5 cm has almost the age of Lekinka cave defined by different the same dissolution rate (-63�2 µm/a) as one at methodologies can be similar� HL-1 = -2�5 cm (-63�9 µm/a)� This is contradictory High dissolution rates in Lekinka (will) have to the expectations of Habič (1966; 18), who some regional effect on hydrology and geomor-assumed high mechanical abrasion along the phology� in comparison with Postojnska Jama channel’s bottom� Since we observed incomplete (Chapter 3�4), Lekinka has a lower entrance dissolution on the tablet’s surface where partly (510�5 m vs� 511�5 m)� Continuous widening and dissolved crystals should be torn away more lowering of Lekinka’s entrance passages due to easily by bed load and suspended sediment, high dissolution rates and consecutive downcut-corrasion surely takes place but it is not increased ting of Črni Potok will result in increasing inci-at the lowest parts of the water channel� The only dence of overflow of the Nanoščica’s water into the hint of corrasion can be a slight decline in rates catchment area of Črni Potok� in december 2008, at L-1, when the water level exceeds HL-1 ≈ 50 cm we were lucky to observe such - nowadays occa- (see Fig� 3�2�14 in Chapter 3�2�3), but this can also sional - overflow (Fig� 3�2�9)� From previous flood be a result of a thicker boundary layer that affects in Otoška Jama on 5 and 6 december 2008 it is rates during backflooding and the consequential evident that the underground waters of the Pivka lowered flow velocity of Črni Potok in Lekinka River in Otoška Jama due to backflooding influ-cave� ences the water level of Črni Potok at the entrance if we assume average dissolution rates to Lekinka when water levels exceed 508 m a�s�l� in (-61�1 µm/a) for the last 12,000 years, about 73 cm Otoška Jama� On 11 december 2008 at the same of dissolution can be expected (dissolution rates in water level, the rise of the water level started very Senonian limestone from Lekinka are almost the quickly (1�2 m/h) but later remained almost stable� same – see Fig� 2�8 in Chapter 2�2�3) and an actual After 4 hours, another even faster rise in the water Figure 3.2.9. Water level of Črni Potok in Lekinka and of the Pivka River in Otoška Jama and rising rate in Lekinka cave. During the first flood between 5 and 6 December 2008, the Nanoščica River did not overflow its banks into Lekinka cave but during the second one (between 11 and 14 December 2008) it did. 85 Case Studies - Lekinka cave level occurred – this event is related to the overflow of the Nanoščica River� The Nanoščica River is re-of the Nanoščica River into the Črni Potok catch- sponsible for only minor dissolution rates in the ment area over a 518-519 m high water divide� Postojna cave system (~-0�1 µm; third measure-The highest water level was reached 30 hours after ment period, Fig� 3�4�4 in Chapter 3�4)� in the case the first rise at HL-1 ≈ 730 cm, when the Nanoščica of a permanent redirection of the Nanoščica River reached its maximum� At that time, outflow into Lekinka cave, which is possible in the future through Lekinka was limited due to the high wa- due to the gradual lowering of Lekinka’s entrance ter level of the Pivka in Otoška Jama, but when the and its high hydraulic permeability, dissolution water level in Otoška Jama declined, the decrease rates in Lekinka will be much weaker; practical y of the water level in Lekinka was very rapid (more all remnants of the old catchment area will be lost than 2�5 m/h), which confirms the good hydraulic and therefore important evidence of speleogen-permeability of Lekinka� Although the water level esis of Lekinka will no longer be observable� We was higher than HL-1 = 30 cm for 69 hours, this ex- suppose that at least some passages of Postojnska ceptional hydrological event did not have any im- Jama were formed in a similar way with higher portant speleological consequences� in Lekinka, dissolution rates due to changes of catchment ar-we noticed some minor transport of bed load and eas – at least at the time when the waters of the medium high dissolution rates (-6�1 µm/15 days), Nanoščica and Pivka sank into the Risovec blind a result of dissolution before or after the intrusion valley (Fig� 3�2�1)� 3.2.2 Measurement location L-1 – vertical variability of dissolution rates At measurement location L-1, water fluctuation may be a result of very low sinter deposition rates was observed from HL-1 = -5 cm to HL-1 ≈ 730 cm� when the water level remains below HL-1 = -5 cm dissolution rates should decrease with height – to (Fig 3�2�6)� Above this level, water is always what extent we tried to determine with a vertical aggressive� Above HL-1 = 0 cm, a steep decline of set of limestone tablets located at measurement dissolution rates was observed, which can be very location L-1� We also tried to find out whether effectively (R2 = 0�99) described using a power the actual cross-sectional morphology of function� An upward decrease of dissolution passages corresponds to the vertical distribution rates is a result of exposure time, although the of present-day dissolution rates� aggressiveness of water most probably increases with the water level� At HL-1 = 7�5 cm, dissolution Vertical variability of dissolution rates was measured drops to half of that recorded at HL-1 < 0 cm� At with 11 limestone tablets on the water gauge 75 m from HL-1 = 25 cm, exposure time is so short that only the sink (Fig. 3.2.5). In the lower section, the distance 10 % of dissolution is observed in comparison between limestone tablets was set to 5 cm, while in the with HL-1 < 0 cm� At HL-1 = 120 cm, dissolution upper section the distance was greater. The procedure and drops to less than 1 % (Tab� 3�2�1)� duration of measurement was the same as was described in The upward decrease of dissolution Chapter 3.2.1. presented in Fig� 3�2�10 and Tab� 3�2�1 is a sum of dissolution measured over 15 days� The results of measurements at L-1 are Fig� 3�2�11 provides better insight into vertical presented in Fig� 3�2�10� dissolution at distribution of dissolution regarding maximum HL-1 = -7�5 cm and HL-1 = -2�5 cm are nearly water level� For better il ustration, 49 individual equal� Slightly stronger dissolution rates at measurements are classified and averaged in HL-1 = -2�5 cm in comparison with HL-1 = -7�5 cm four classes regarding maximum water levels 86 Case Studies - Lekinka cave during 15-day measurement periods� The third zone of maximum water level turned out to be the most frequent (and therefore the most representative) over 15 day periods� in general, the lowest the maximum water level results in the highest vertical decrease of dissolution� during such a hydrological regime the most evident wall notch could be formed� The most gradual transition of a wall notch into the vertical wall could be expected with a high oscil ation of water levels due to flush floods� it is interesting that dissolution below HL-1 = 5 cm is the highest in the third class and not in the fourth, which is a result of lower dissolution rates at the lowest limestone tablets when the water levels exceed HL-1 = 50 cm� decrease of dissolution rates is possible through slower water flow which decreases corrasion rates and the rate of tearing away partly dissolved crystals or/and reduces dissolution rates through a thickening of a diffusion boundary layer� A strong decrease of dissolution with height (Fig� 3�2�10) has an important speleogenetic consequence – the upper part of a passage suffers almost no dissolutional transformation while the lower part widens and incises� The ratio between widening and incising depends on the morphology of a passage and fluvial transport of bed load material� The latter protects the Figure 3.2.10. Decrease of dissolution with height bed of a passage against dissolution or at least measured at L-1 from 14 November 2006 to severely reduces incision of a passage, while the 8 January 2009 (786 days). widening of the passage continues in both lateral directions� Long term continuation of such a process would result in vast lateral extension in the lower part of a passage that even enhances further sedimentation of bed load material due Table 3.2.1. Portion of dissolution at different height at measurement location L-1 in comparison with the lowest two limestone tablets at L-1 between 14 November 2006 and 8 January 2009. Height of limestone tablet (cm) -7�5 -2�5 2�5 7�5 12�5 17�5 27�5 42�5 62�5 87�5 117�5 Portion of dissolution 100�0 83�6 50�9 30�2 18�5 7�2 4�2 2�1 1�7 0�9 with the lowest 2 lime- stone tablets at L-1 (%) 87 Case Studies - Lekinka cave to decreased depth/width ratio (Skinner et al� on (a) vertical variability of dissolution rates 2004; 365)� Since such morphology is absent in and (b) fluctuation of water levels – the smallest Lekinka cave, long-term accumulation of bed radius (this means a steep transition from load material has not been characteristic for bottom to wall) is expected if vertical variability Lekinka as a result of (a) limited availability of of dissolution rates is high and oscil ation of such material, (b) high dissolution rates and (c) discharge is low� due to strong dissolution rates fast water flow that distributes bed load over an even at lower and medium water levels and quite extensive surface that is then more susceptible to weak rates at high water levels, quite a sharp dissolution� transition between vertical wal s and the bed of a Vast lateral extension of the lower part channel is expected in Lekinka if the present-day of a passage could also be possible without processes are equilibrated with cross-sectional accumulated bed load if the lower wal s are morphology� Although it is difficult to observe perpendicular to the water level� in such a clear examples of vadose meanders in Lekinka, case, water widens the passage twice as quickly in the case of Fig� 3�2�12, the transition between as it incises (since the widening takes place the bed of the channel and the vertical wal s is in two directions and incision only in one)� quite sharp, which proves that the majority of in reality, wal s and beds of channels are not dissolution occurs during low and middle water truly perpendicular to each other as they are levels, which is in agreement with expectations� transitional� For uniform incision of a vadose At measurement location L-1 (Fig� 3�2�4), the meander, an equilibrated shape of the lower wal s are perpendicular to the bed of the channel part of the meander has to be established (Fig� since the latter is covered by bed load material� 3�2�12)� The radius of curvature between vertical Such conditions favour the formation of wall wal s and the bed of a channel depends strongly notches� Actual wall notch morphology more Figure 3.2.11. Comparison between average dissolution at individual height and dissolution HL-1 < 1 cm with regard to four different zones of maximum water level. Data represented in this figure were obtained at measurement location L-1 from 14 November 2006 to 8 January 2009. 88 Case Studies - Lekinka cave or less corresponds to the vertical decrease of bed load material inside and outside the cave, dissolution presented in Fig� 3�2�10� General y, the which could have been climatical y driven during wall notch extends about 14 cm into each lateral the last (Würmian) ice Age� According to our direction, which would correspond to about measurements, dissolutional development of a 2,300 years of dissolution at annual dissolution wall notch caused by bed load accumulation is rates -61�1 µm/a� possible since the accumulation holds up incision Above HL-1 = 75 cm, a fossil wall notch can be but does not inhibit the lateral extension of recognized (Fig� 3�2�4)� According to Gospodarič passages� decreased supply of bed load material and Habič (1966), this wall notch could correspond is followed by a gradual complete removal of bed to the lowest accumulation terrace of Črni Potok� load material and the subsequent incision forming Two higher wall notches, which are mildly a new vadose meander, whose width corresponds developed at L-1 but can be observed several to the most effective width of channel regarding tens of metres downstream, should correspond discharge and dissolution during higher water to two even higher accumulation terraces in the levels� According to the present-day dissolution Črni Potok catchment area (Gospodarič & Habič rate (-61�1 µm/a), the end of fossil wall notch 1966; 27)� According to Gospodarič and Habič, development and the beginning of incision would the development of wall notches corresponds date to 12,300 years B�P�, which corresponds to to increased production and accumulation of the Younger dryas stadial� Figure 3.2.12. Typical meander cross-section about 300 m from Lekinka’s entrance, where the cross-sectional area reflects uniform incision of a meander without significant widening. Wall notches are the result of past events (photo: Mitja Prelovšek). 89 Case Studies - Lekinka cave 3.2.3 Measurement locations L-2, L-1, L-3, L-4, L-5, and L-6 – longitudinal variability of dissolution in the entrance part of Lekinka (along a 250 m long watercourse) A decrease in dissolution rates from the entrance the limestone tablets were mostly under the water level. to the inner part of a cave can be expected in At very high discharge the limestone tablets were under all kinds of ponor caves where the water is very slow flowing water since the Pivka River in Otoška Jama aggressive at the entrance� A similar case on the caused backflooding in Lekinka. Measurements at L-2, L-1, surface of contact karst was studied by droppa in L-3, L-4 and L-5 started on 15 April 2007 and finished on the valley of demänova (Gams 1985; 368), where 5 April 2009. the dissolution rates in the middle of a limestone Spatial measurements of physicochemical properties of valley fall to 14 % of dissolution rates detected water (SEC; T and pH) were done using a WTW Multiline at the first contact with limestone� downstream, P4 in different hydrological conditions. where the river leaves the limestone valley, dissolution rates were only slightly lower (12 % of The highest dissolution rates most probably dissolution rates detected at the first contact with take place 30 m before the entrance to Lekinka, limestone)� in general, the decline in dissolution where Črni Potok interacts with the first rates is related to the increasing saturation of limestone blocks in the water channel� Further water along its flow over the karstifiable rocks� dissolution rates are presented in Fig� 3�2�13� Bray (1972, 1977) asserts that downstream dissolution rates become weaker between the decrease of dissolution rates in ponor caves first (L-2) and last (L-6) measurement locations, can be reduced due to gradual decay of organic which is as expected� Although we would expect matter that increases the concentration of that weakening of dissolution rates is due to the H+ in the water� The same phenomena can be dissolution of limestone, further study (Covington expected in Lekinka cave� Through longitudinal et al� in press) suggests that the outgassing of CO2 dissolution measurements, we tried to quantify from the water is responsible for weakening of the level of decreasing dissolution rates at dissolution rates� The greatest deviation is noticed different discharges, to determine the most at L-4 due to slowly flowing water, which reduces relevant factors that control dissolution, and to the R2 of the best fit exponential correlation link present-day speleogenetic processes with from 0�99 to 0�97� Nevertheless, the difference actual cave morphology� is relatively slight (10 % between expected and actual dissolution)� According to Fig� 3�2�14, the The longitudinal variability of karst processes was highest deviation between L-4 and all others studied at six locations. The procedure and interval of measurement locations appears at middle water measurement was the same as at L-1 (Chapter 4.2.1). levels (between HL-1 ≈ 22 cm and HL-1 ≈ 50 cm), The first measurement location (L-2) was located 40 m when differences in flow velocity and the effective from the entrance, the second (the lowest limestone tablet dissolution are the highest� At lower water levels, at L-1) 75 m, L-3 115 m, L-4 145 m, L-5 205 m and L-6 dissolution is absent downstream of L-1, while at 250 m. Measurement locations L-2, L-1, L-3, and L-5 were higher water levels, flow velocities are similar at characterized by fast flowing supercritical turbulent flow all measurement locations due to backflooding� with velocities of about 0.5 m/s during middle discharge. Lower rates are the result of a thicker diffusion Measurement location L-4 was located in a 1.6 m wide and boundary layer (Liu & dreybrodt 1997), lower 0.4 m deep water channel. Therefore, at L-4 water flow was corrasion rates or/and the reduced mechanical subcritical and at least 10-times slower in comparison with force of flowing water that tears away partly the other locations. During the time of very low discharge, dissolved calcite crystals� 90 Case Studies - Lekinka cave The decrease of dissolution from L-2 to L-6 can enters Lekinka� during such low water levels, easily be described with a logarithmic equation, dissolution between L-2 and L-6 is not increased which fits the real data quite well (R2 = 0�97; even due to the decay of organic matter or higher Fig� 3�2�13)� This means that the weakening of CO2 concentrations (up to 1,440 ppm) during the dissolution is the greatest near the contact (by summer months� At measurement locations L-2 37 % per 100 m of water course between L-2 and and L-1, the first dissolution rates were detected L-3), while further from the contact, the drop when the water level exceeded HL-1 = 0 cm of dissolution rates is much lower (by 27 % per (Q ≈ 7 l/s)� during such water levels, differences 100 m of water course between L-3 and L-6)� in in dissolution rates between L-2 and L-1 on one spite of this, the drop of dissolution rates during side and all other measurement locations on the the first 250 m of underground flow is very high other are the greatest, since dissolution is absent (54 %)� Regarding the equation in Fig� 3�2�13, at downstream of L-1 (Fig� 3�2�14; groups of averaged the end of Lekinka (after 790 m of water flow) values correspond to zones already defined in dissolution of about -18 µm is expected during Chapter 3�2�2)� downstream of L-2 and L-1, the measurement period, which is only 12 % dissolution appears at slightly higher discharge, of the dissolution rate measured close to the when the water level exceeds HL-1 ≈ 10 cm� if the entrance (L-2)� maximum water level exceeds HL-1 ≈ 10 cm but The decrease of dissolution rates presented remains below HL-1 = 22 cm, dissolution at L-6 in Fig� 3�2�13 is not constant but fluctuates amounts to 32 % of the dissolution measured significantly during different discharges at L-2� A further rise of the maximum water (Fig� 3�2�14)� At very low water levels (HL-1 < 0 cm), level leads to higher absolute but lower relative water is already saturated before Črni Potok differences between measurement locations, but Figure 3.2.13. The results of 15-day dissolution measurement intervals at L-2, L-1, L-3, L-4, L-5, and L-6 from 5 April 2007 to 5 April 2009. 91 Case Studies - Lekinka cave only to HL-1 = 50 cm, when absolute differences observed between tributaries (although the remain the same even at higher water levels due water level was low), which indicates dissolution, to backflooding� Lower dissolution rates due to tributaries are much more responsible for total decreased velocity of flow were also confirmed hardness increase (Fig� 3�2�15)� Their contribution with measurements at L-4 (Fig� 3�2�13)� to total hardness increases with increased Gospodarič and Habič (1966) measured the discharge of the main water course due to the total hardness of Črni Potok between Ponor high quantity of water and high flow velocity of and Končni Sifon� They attributed the growth the cave stream that reduces the reaction of water in total hardness to dissolution, but dissolution with limestone� during such high discharge, is not the only process that increases the total the rise of SEC over the first 250 m of the cave hardness of water along a cave stream� From the amounts to up to 3 μS/cm (12 %), while the rise of entrance to 250 m into Lekinka, four tributaries SEC contributed by tributaries amounts to about fed by autogenic percolation water join the 23 μS/cm (88 %)� during low discharge, changes main water course� They have high SECs and in total hardness along the cave stream are much very stable temperatures during the year� Since greater due to more effective reaction of water the outgassing of CO2 can be observed along with limestone walls� during low discharge, their accessible water passages, tributary waters dissolution is responsible for a 26 μS/cm (26 %) should flow through the karst massif with higher rise of SEC, while the tributaries contribute up to CO2 partial pressure in comparison with a well 74 μS/cm (74 %)� ventilated main passage� The first right tributary downstream the decrease of dissolution rates deposits sinter due to the rapid outgassing of CO2 influences morphology differently in meanders and consequential rise of SiC� Although the rise and in passages characterized by deeper water of SEC as a proxy for total hardness was always in pools� The width of pools should decrease Figure 3.2.14. Average dissolution within each of four classes of maximum water level at measurement locations between Ponor (L-2) and the first pool 250 m from Ponor (L-6). Data are calculated from measurements that began on 15 April 2007 and ended on 5 April 2009. 92 Case Studies - Lekinka cave downstream along 250 m from the entrance to the downstream decrease of dissolution rates passages� At the places where vadose meanders but in agreement with the longer exposure time are developed, the width of the meander depends of pools downstream, enhanced by backflooding only on discharge and generally speaking not on from the underground Pivka River� differences in dissolution rates� Consequently, Gospodarič and Habič (1966; 14-15) were the downstream decreases of rates results only in first to notice three wall notches that gradually the decrease of the longitudinal gradient due disappear about 300 m from the entrance� Ac-to more intensive dissolution rates close to the cording to them, wall notches disappear due to entrance� due to stronger dissolution rates, the sumps, which were located about 300 m from the meanders should be higher close to the entrance� entrance and hindered high-middle discharge, Since the dissolution rates are lower in pools and and should be formed at the times of high dis-higher in meanders, a gradual transition from charge� However, this explanation is controver-pools to meanders should be characteristic if the sial if we know that backflooding more common-water level does not inhibit the incision of the ly creates the phreatic enlargement of passages meanders� The latter transition should result in and not wall notches� According to our observa-an increase of pools from the Ponor to the Končni tions in Lekinka cave, wall notches develop if (a) Sifon� All this is in agreement with present-day water is aggressive at low and middle discharge, morphology (Gospodarič & Habič 1966) since (b) water oscillations are low and (c) water trans-the height of passages generally decreases from ports bed load material which protects the bed of the Ponor to the Končni Sifon and the portion of a channel against dissolution� Since we have no passages developed as meanders decreases from evidence that the conditions were much different the entrance� Nevertheless, the width of pools in the past, the formation of fossil wall notches increases downstream, which is contradictory can be attributed to the same factors� Figure 3.2.15. Growth of SEC due to dissolution (D) and due to four tributaries (T) characterized by high total hardness. 93 Case Studies - Lekinka cave 3.2.4 Measurement locations L-2, L-1, L-3, L-5, L-6, L-7, L-8, L-9, and L-10 – longitudinal variability of dissolution rates all along the underground water course in Lekinka (from the entrance to the sump) in Chapter 3�2�3, measurements were made only rates weaken by 55 %� This is much lower than along the first 250 m of Lekinka cave� Further expected (88 %) with extrapolation of dissolution into the cave, several deep and long pools make rates from the first 250 m of the cave (Fig� 3�2�13)� access more complicated and measurements more Results demonstrate that dissolution rates difficult to take� Therefore, much longer intervals remain more or less constant downstream were chosen for dissolution measurements along from L-6 since the outgassing of CO2 from the the complete cave stream to the Končni Sifon water decreases due to a very low longitudinal (790 m)� gradient downstream from L-6 and deeper and longer pools� Between L-2 and L-10, the decrease Dissolution measurements at L-7, L-8, L-9, and L-10 of dissolution rates is higher during the first began on 13 February 2008 and finished on 17 April 2009. measurement period (by 64 %) in comparison Between these dates, limestone tablets were replaced once with the second measurement period (by 49 %; on 5 September 2008. The procedure of weighing and fixing Tab� 3�2�2)� This is a result of much higher was the same as at L-1 (Chapter 3.2.1); only the exposure discharge during the second measurement time and number of exposed limestone tablets at each period, which can also be observed from higher measurement location (3 vs. 1) were different. Measurement dissolution rates in the entrance part of Lekinka location L-7 was located 340 m from the entrance, L-8 510 (Tab� 3�2�2)� m, L-9 630 m and L-10 750 m. Limestone tablets were placed Although dissolution decreases more or in similar hydrodynamic conditions, at least during low- less constantly between L-2 and L-10, some middle discharge (supercritical turbulent water flow). For results show other poorly examined factors comparison we took into account results from measurement that can increase or decrease dissolution rates locations L-2, L-1, L-3, L-5, and L-6, which are the sums of along an allogenic cave stream� The greatest data from 15-day measurement intervals. differences were produced during the second measurement period, when discharge were the The results of the measurements are presented highest (Tab� 3�2�2)� during high discharge, in Fig� 3�2�16� Between L-2 and L-10, dissolution the most distant limestone tablets are the most Table 3.2.2. Dissolution rates in Lekinka measured out from the Ponor to the Končni Sifon from 13 February 2008 to 17 April 2009. L-2 L-1 L-3 L-4 L-5 L-6 L-7 L-8 L-9 L-10 First measurement -72�9 -76�9 -65�5 -45�4 -50�7 -39�9 -40�7 -30�1 -29�5 -26�4 period (µm/a; % of dissolution at L-2) 100 106 90 62 69 53 56 41 40 36 Second measurement -85�3 -77�7 -58�4 -51�5 -43�0 -40�2 -54�2 -56�8 -40�8 -43�2 period (µm/a; % of dissolution at L-2) 100 91 69 60 50 47 64 67 48 51 94 Case Studies - Lekinka cave Figure 3.2.16. Decrease of dissolution between Ponor and Končni Sifon. Dissolution at L-2, L-1, L-3, L-4, L-5, and L-6 is the sum of 15 day dissolution measurement intervals. influenced by aggressive water� Additionally, and downward directions, while in vadose hydrodynamic and hydrochemical differences meanders, by far the highest downward incision between measurement locations are the lowest is characteristic� Therefore, phreatic passages during high water levels� This is demonstrated should be wider but lower in comparison with by the dissolution rates at L-4 during the second meander-type passages, which is consistent measurement period when we were not able to with the actual morphology of Lekinka� due to observe the influence of usually slowly flowing a sometimes higher reaction surface, the cross-water on lower dissolution rates due to a thicker section of phreatic passages far from the entrance diffusion boundary layer that is responsible is often larger than the cross-section of meander-for slower diffusion of H+ ions to the limestone type passages close to the entrance, although surface (dreybrodt 1988; 113)� On the contrary, dissolution rates are much higher at the entrance� it seems that that poorly understood factor is The direction of enlargement of downstream responsible for the increase of dissolution rates passages in Lekinka also depends on the height at L-7 and L-8 rather than the decrease of rates at of the Pivka River in Otoška Jama – if the latter L-6, L-9, and L-10� is high, dissolution can also take place on the in Lekinka, the aggressiveness of water ceiling� supports the enlargement of the underground downstream decrease of dissolution rates and passages all along the water course at high rates backflooding from the Pivka River result in the (-77�4 µm/a at L-2 and -35�7 µm/a at L-10)� The important morphological transition from the direction of passage enlargement depends on Ponor to the Končni Sifon� Meanders are typical the morphology of present-day passages – in for passages close to the entrance� The longest phreatic ones, dissolution takes place in lateral (~350 m with very short phreatic passages) and 95 Case Studies - Lekinka cave the tallest meander developed in the entrance water flow in vadose conditions (Häuselmann zone, while the downstream part of Lekinka is 2002; 98, Häuselmann 2007) but can be absent mostly formed in several metres wide phreatic if the passage is ful y flooded only occasional y passages� At many places, vertical incision in epiphreatic conditions (Palmer 2002)� A downward from the initial y phreatic passage consequence of backflooding is also a reduction can be observed (Fig� 3�2�17), which is a result of flow velocity through Lekinka cave, which is of the adaptation of the longitudinal profile to reflected in quite rare and over 5 cm long scallops the level of the Pivka River� Such transitions are found close to the Končni Sifon while the scallops common in caves which were initial y formed in in the entrance meanders are several centimetres phreatic conditions and followed by aggressive shorter� Figure 3.2.17. Incision of vadose meander on the bottom of an initial y phreatic passage (photo: Mitja Prelovšek). 96 Case Studies - Lekinka cave 3.2.5 Conclusion Lekinka cave drains a marshy catchment parts in the cross-sectional profile� The upward area about 1 km2 wide with low inclination decrease of dissolution is rapid (50 cm above low and low carbonate content in soils� Therefore water level, only 3 % of dissolution measured the water of Črni Potok that flows into Lekinka in the bed of the channel was detected), which is highly undersaturated with respect to Ca2+, indicates relatively constant discharge with which results in high dissolution rates at the occasional flush floods and the most expressed entrance and further toward the Končni Sifon� dissolution during low-middle water levels� On average, dissolution rates at the entrance Therefore an upper part of the passage remains amount to -61�1 µm/a� 750 m from the ponor, dissolutionally almost unchanged, while the dissolution rates still amount to -38�2 µm/a� if lower part incises downward or laterally� The such rates are characteristic for longer periods, prevailing direction of enlargement depends on rapid enlargement of Lekinka cave can be dated the present-day passage cross-section and supply to the lower Würmian glaciation� of bed load material� The latter reduces downward The rate of dissolution mainly depends on incision and supports lateral extension of the discharge, which is a function of the amount passage and hence the formation of wall notches� of precipitation, evapotranspiration and snow The formation of wall notches could not be retention� Therefore, the highest dissolution rates possible in the case of very high and frequent were observed during autumn, spring and winter water fluctuation or an absence of aggressiveness months, while the lowest are characteristic for during low-middle discharge� A wall notch that summer months� This corresponds to the rain- is developing in present-day conditions started snow discharge regime with the highest peaks in to form about 2,300 years B�P� and the higher one autumn and spring and in winter-spring, when can be dated to the Younger dryas stadial� By far the snow is melting� during very low discharge downward incision is the most characteristic (Q<7 l/s), water is at equilibrium and dissolution for meander-type passages, which are mainly rates are absent� during low discharge (Q≈7 l/s), vertical in their upper part but rounded close to dissolution can be detected with limestone tablets the bed of the channel� At middle water levels, successfully about 100 m from the ponor� Further when the dissolution is the most expressed, walls into the cave, dissolution rates can be detected form with water levels at an angle slightly higher during higher discharge and can amount to up to than 90º� Only such a shape supports vertical -9 µm/15 days� The highest dissolution rates are incision of passages� in pools, dissolution rates not characteristic for the highest discharge but are slightly lower in comparison with meanders rather for long-lasting middle-high discharge� but dissolution does takes place in a downward Seasonal variation as a result of fluctuation of and lateral direction� air and water temperature, CO2 production or downstream, dissolution rates decrease� in content of organic acids, was not recognized� the first 250 m of underground water flow, the Corrasion seems to be relatively low although decrease of dissolution rates can be described high turbidity of water can be observed at high- with an exponential function most probably middle discharge� Lower rates are expected due to the outgassing of CO2 from the water in pools, where slow water flow thickens the (Covington et al� in press)� downstream from diffusion boundary layer and decreases the 250 m to the confluence with the Pivka River, diffusion rate of H+� dissolution rates are nearly constant� Although dissolution is concentrated in the lower at least eight tributaries with high total hardness 97 Case Studies - Lekinka cave and high partial pressure of CO2 were detected entrance part, which influences the longitudinal along the cave stream, they are not strong enough profile� Ongoing incision will result in retrograde to turn dissolution into sinter deposition� lowering of the water divide with the Nanoščica downward incision in the downstream River, which can use Lekinka cave as a permanent part of Lekinka is influenced by the Pivka shortcut to Otoška Jama due to its lower entrance River in Otoška Jama� The Pivka River causes in comparison with Postojnska Jama� if capture backflooding in Lekinka and therefore hinders does occur, dissolution rates will be significantly the process of prevailing downward incision, reduced in Lekinka� (Over)saturated water at especially near Končni Sifon� Therefore, phreatic low and middle discharge and slightly aggressive cross-sectional morphology is more common in water at high water levels will enhance passage the downstream part of Lekinka� deeper incision enlargement at phreatic conditions and obstruct is possible and can be observed especially in the wall notch formation� 98 3.3 ŠKOCJANSKE JAME Škocjanske Jame (Škocjan caves; Reg� No� 735) in Škocjanske Jame, scientific research started together with the morphological phenomena of as early as in the second half of the 19th century the underground Reka River presents the greatest (for details see Habič et al� 1989; 7), but serious and natural curiosity of the whole Classical Karst extensive speleological research within the cave it-between the Gulf of Trieste and Vipava Valley� self began in the 1980s� The geological structure, Together with the blind valley of Vreme and long-term speleogenesis and first datings were divaški Kras (divača karst) along the narrow done by Gospodarič (1983, 1984)� He developed ponor border of the Reka River they comprise a 4-phase model of development of Škocjanske part of a typical morphogenetical unit of contact Jame from the primary horizontal passages to the karst, unique in Europe regarding its phenomena final Würmian vadose incision of Hankejev Ka-and dimensions (Gams 1983)� due to its extreme nal (Hanke’s channel)� development of the latter dimensions and unique karst landscape with an is likely related to a colder climate given the huge early and rich history of explorations, Škocjanske production of gravel, while the warmer periods Jame were listed among uNESCO natural and likely correspond to the more gentle development cultural heritage of the world in 1986� Škocjanske of Škocjanske Jame with its accumulation of sinter Jame are known also because of the existence of (Gospodarič 1983, Gospodarič 1984)� Transport of one of the largest underground chambers in the sediment through Škocjanske Jame was studied by world (Martelova dvorana - Martel’s chamber), Kranjc (1986)� in the 1980s, Kogovšek (1984) took which is 308 m long, up to 123 m wide and up under consideration vertical percolation of water to 146 m high� The volume of this chamber, in Škocjanske Jame, which dissolves carbonates through which the Reka River flows, is estimated in the epikarstic zone and deposits them in some to be 2,100,000 m3 (Mihevc 2001; 79)� passages in Škocjanske Jame� Later, the lithologi- The first real exploration of the entrance area cal structure with emphasis on initial develop-along the underground water course began in ment of the channel along bedding planes was in-the 1st half of the 19th century, when 500 m of vestigated by Knez (1996)� The speleogenetic study cave was examined (Habič et al� 1989, 4)� Further of the whole system and the first measurements of research was much more difficult, since the water its processes were made by Mihevc (2001), while flows in a narrow passage with steep walls and Slabe (1992, 1995; 109) examined the micro-mor-over several waterfalls� Nevertheless, new explo- phology of the water channel� Lastly, scientific reration which was started in 1884 by deutscher search brought some new information on water und Österreichischer Alpenverein (German and oscil ations and the physicochemical characteris-Austrian Alpine Club) from Trieste ended in tics of underground water flow, which was carried 1890 at the terminal sump� The latter was suc- out by monitoring flood pulses at many under-cessfully dived in 1991 and in recent years, but a ground sites between Škocjanske Jame and Tima-connection at least 900 m long with Kačna Jama va spring (Cuchi & Zinni 2002 after Gabrovšek & downstream is still under exploration� Peric 2006; 37, Gabrovšek & Peric 2006)� 99 Case Studies - Škocjanske Jame Geological and geomorphological without interruptions (Mihevc 2001; 83)� Finally, characteristics the present-day keyhole passage was formed� The Škocjanske Jame are located about 7�5 km underground active passages of Škocjanske NW from the contact between Eocene flysch Jame are rich in corrasional and dissolutional rocks and older Cretaceous limestone� A micro-features, which spatially alternate among whole stratigraphic sequence of Carboniferous each other� Corrasional features (potholes, pol-rocks is located in a low tectonically deformed ished surfaces, scratches) are related to the ex-monocline, which is inclined at 20-35º toward ceptionally high amount of transport of alloch-the SSW (Gospodarič 1983; 165)� Therefore, the thonous material from the Reka River catch-youngest sediments (Eocene flysch rocks) are ment area (Kranjc 1986)� Corrasion rates were found in the SSW and the oldest (thick-bedded measured by Mihevc (2001; 65) with a MEM at to non-bedded Turonian limestone) are found in 17 measurement locations� Over 6 years of meas-the NNE (Gospodarič 1983, Knez 1996)� Between urements, the highest values were found at plac-them, very pure (the portion of CaCO3 usually es where the pebbles are hitting the wall (from exceeds 99�5 %; Knez 1996) micrite bedded -160 to -40 µm/a) while much lower values were Senonian and thin-bedded Paleocene limestone measured at places of polishing (about -20 µm/a)� are developed� All known passages of Škocjanske dissolutional features (scallops) show that we can Jame are located within thick-bedded or non- also expect some dissolution rates� dissolutional bedded Senonian and Turonian strata, except and corrasional features are only developed in Tiha Jama (silent cave; southwestern, today dry, the lower 1-5 m high portion of the water chan-passage of Škocjanske Jame), which developed in nel� Higher, the wall is weathered by mechanical thin-bedded limestone� Thick-bedded carbonate breakdown or condensation corrosion� Another rocks are nowhere highly tectonically damaged, very intensive process in the underground water which supports the development of long and channel is sinter deposition due to percolation high passages without significant collapses� water, which takes place even at the bottom of From a speleogenetic point of view, the Hankejev Kanal (Slabe 1992; 198, Mihevc 2001; most important geological structures for the 74)� The location of sinter formations suggests formation of Škocjanske Jame are five tectonised that sinter deposition is higher than dissolution bedding planes, where the initiation of the – at some places even higher than corrasion� first phreatic passages took place (Knez 1996)� The enlargement of passages in Škocjanske Later, the development of Škocjanske Jame Jame is crucial for development of the superficial was characterized by the incision of a vadose upstream catchment area and the downstream meander in epiphreatic conditions� The most karst aquifer� The caves are the only points impressive incision is the 570 m long Hankejev where an upstream water and sediment (about Kanal (Hanke’s channel), where the initiation 242�4 Mm3 of limestone and much more flysch of the first phreatic passage started in the upper rocks; Gams 1962; 267) can be drained through bedding plane, denoted 300 (Knez 1996; 23-24)� the aquifer� Škocjanske Jame act as a restriction in continuation, the passage incised by about for the lowering of longitudinal profile since the 90 m to the stratigraphically lower bedding highest gradient is observed here� Where the planes (called 400 and 500, in Martelova dvorana Reka River flows over flysch rocks, the average also 600, 700; Mihevc 2001; 60) and formed a gradient is 2�8 ‰� Between the lithological deep meander with almost vertical walls� At the contact of flysch with limestone and ponor bottom, Hankejev Kanal is on average 10 m wide� (the hydrological beginning of Škocjanske The lack of significant lateral extension in the jame), along a 7�1 km water flow through the cross-sectional profile indicates regular incision narrow gorge, the gradient is increased to 5 ‰ 100 Case Studies - Škocjanske Jame (Mihevc 1991)� in Škocjanske Jame, the gradient several tens of metre high floods in Martelova increases to 45 ‰ (Habič et al� 1989; 12) while dvorana usually occur every year� At the highest the continuation of underground flow continues discharge (for example in 1826), water can rise with an average gradient of 6�3 ‰� Therefore, the 132 m above the medium water level in the critical point for water flow and also erosional final lake in Martelova dvorana (Boegan 1938 base for the catchment area of the Reka River is after Habe 1966; 47) and flood the bottom of all in Škocjanske Jame, since all the water must be passages except Tiha Jama� conducted through one passage� downstream in Therefore, the characteristics of the catchment the aquifer restrictions are more easily avoided area are extremely important for geomorphic since the water flow braids to several semi- activity in Škocjanske Jame� According to parallel flow paths� The dissolutional character several sources (Rojšek 1983; 52, Kranjc & of the Reka River plays an important role in Mihevc 1988 after Mihevc 2001; 52, Habič et al� underground gradient, since it defines the speed 1989; 10, uhan 2007), the catchment area of the and where the restrictions can be removed� Reka River extends from over 332 to 378 km2� Karstified carbonate rocks (mainly Cretaceous Hydrological characteristics limestone) cover about 28 % of the catchment The free-surface underground course of the Reka area, especially in the SE part, from where the River is 2�7 km long and usually 3-15 m wide Reka River receives some important springs at at medium water levels (Kranjc 1986; 112)� At the contact with flysch rocks� The latter extend average discharge, from 8�26 to 8�95 m3/s (uhan over 60-74 % of the catchment area, mainly at the 2007, Mihevc 2001; 52) passes by the hydrological Brkini Mountains (Kranjc 1986; 112, Habič et al� station 7�5 km upstream from the ponor to the 1989; 10, Kranjc & Mihevc 1988 after Mihevc Škocjanske Jame� About 1 m3/s is lost in the 1991)� For the superficial drainage system, water channel immediately downstream from which is developed on this fluvio-denudational the contact between flysch rocks and Paleocene relief, fast runoff with short and high peaks in limestone and some more water further discharge is characteristic� This has important downstream (Radinja 1967 after Mihevc 1991)� consequences regarding the discharge duration This sub-parallel water course does not appear curve, which (with a very concave form) shows in Škocjanske Jame (Habič et al� 1989; 11)� in great differences in discharge with a relatively Škocjanske Jame, no important tributaries or small percentage of medium discharge� The sinks were noticed at low and middle water levels torrential character of the Reka River can (Mihevc 2001; 62)� also be seen from a comparison of the lowest in the case of strong precipitation, the rapid (0�16 m3/s; uhan 2007) and the highest observed response of Reka discharge can be observed� The discharge (305 m3/s; uhan 2007), since it highest discharge was measured in 1972, when it amounts to 1: 1,906� Streams from the Brkini reached 305 m3/s (uhan 2007), while the highest Mountains decrease total hardness of the Reka discharge with a recurrence period of 100 years River downstream of the karst springs from is estimated to be 453 m3/s (ZVSS 1978 after Mt� Snežnik� Nonetheless, this decrease is Mihevc 1991)� not so important since the total hardness falls Allogenic recharge has strong control over the from 10�7 ºNT to a still high 10�3 ºNT between hydrological conditions and cave development� springs below Mt� Snežnik and flysch-limestone The most evident consequence is flooding, since contact (Gams 1962; 278)� Only a small amount the outer river channel supports high discharge of the catchment area (12 %; Kranjc 1986; 112) is amounts while the narrows in the cave function covered with nonconsolidated alluvial sediments as restrictions at high water levels� Therefore, along the Reka River and its tributaries� 101 Case Studies - Škocjanske Jame Another very important influence of the Reka and catchment area in siliciclastic flysch River is the transport of suspended and bed load rocks, expected dissolution rates may be high, material� Since the Reka River valley has only especially at high discharge� Occasional spatial one possible outlet through Škocjanske Jame, all measurements of total hardness of the water the material that once filled the Reka River valley in the Reka River gorge at middle water levels was washed away through the cave� in the cur- (Gams 1962, 1966b) does not prove this� Even at rent situation, on average 30,000 m3 of material high discharge rates, dissolution seems to be low is transported every year through the Škocjanske since Gams (1966b) detected relatively high total Jame (Kranjc 1986)� The majority of flysch ma- hardness (9�7 ºN) and Mihevc (2001; 64) very low terial is transported as bed load (83 %; Kranjc dissolution rates, as measured by MEM� The high 1986; 114) and the rest (17 %) as suspended load� total hardness of the Reka River is a result of karst Below the flysch-limestone lithological contact, springs that feed the main water course of the the percentage of flysch pebbles strongly de- Reka River under Mt� Snežnik and a result of the creases (by 8�5 % per km of water course; Kranjc dissolution of calcite cement between particles 1983 after Mihevc 1991)� it is very significant that in flysch� Cement comprises from 20 to 24 % of the percentage of flysch pebbles is not reduced the flysch rock� Nevertheless, the cement in the just due to rounding, which would indicate cor- catchment area can also be siliceous (Šikić & rasion, but rather due to crushing, which was Pleničar 1975; 22); therefore high differences can confirmed by the almost longitudinally stag- be expected in total hardness among tributaries nant index of roundness (Kranjc 1986; 114)� Al- from the Brkini Mountains� though the crushing of pebbles is recognized as an important process that leads to the reduction Meteorological characteristics of flysch pebbles downstream from lithologi- due to its two natural big entrances, all passages cal contact, the longitudinally stagnant index of Škocjanske Jame (except Tiha Jama) are very of roundness could not be possible without the well ventilated� Especially during summer and rounding of freshly crushed pebbles� The trans- winter, when temperature differences inside and port of flysch material can be an intensive pro- outside are the highest, strong air currents can cess for high corrasion rates if the crushing and be felt all along the water channel� in winter, cold rounding occurs at the contact with a limestone air enters the cave through the lower entrance water channel� Since the superficial and under- and if the outer temperatures remain below ground water channel is mostly formed in solid 0 ºC for several days, which is common due to limestone (Kranjc 1986; 112, Mihevc 2001), and temperature inversion in the collapse dolines, only in some parts is the river bed covered with freezing along the underground Reka River is pebbles and breakdown material (for example, in common all along the Martelovo Jezero (Martel’s Martelova dvorana), the transport of flysch ma- lake)� Warmer air exits the cave under the terial definitely is an important process responsi- roof� during summer, air flows in the opposite ble for high corrasion rates, as already confirmed direction� Since the outer air cools down near the by Mihevc (2001; 65)� Another important process cave’s roof, relative humidity approaches 100 % is mechanical erosion and the transport of lime- and condensation appears� For this reason, stone blocks, since the percentage of limestone dripping from the roof and walls is abundant in increases from 0 % at the lithological contact to Hankejev Kanal (Mihevc 2001; 63)� 20 % at Škocjanske Jame (Kranjc 1986; 114)� in Tiha Jama, annual temperature differences dissolution is a much lesser known process are very low due to weak ventilation� Air in the Reka River in comparison with corrasion� temperature fluctuates between 11 and 12�5 ºC Regarding the high oscillation of discharge (Kogovšek 1983 after Habič et al� 1989; 13)� 102 Case Studies - Škocjanske Jame 3.3.1 Measurement place S-1 and S-2 – temporal variability of processes at Swidovo Razgledišče The first measurements of dissolution in already by Gams (1996; 103), who failed in Škocjanske jame were made by Mihevc (2001; making measurements with limestone tablets in 64)� Although MEM measurements were made Škocjanske Jame� after several years of exposure, results showed Our first observation was done during a test dissolution rates in the range of the measurement study in a relatively remote (non-corrasional) error (-10 µm/a)� To observe dissolution even in place in Hankejev Kanal (Chapter 2�2�2)� shorter intervals, measurements using limestone Results confirmed low intensity of dissolution tablets seem to be the only possible way� The only (-1�6 µm/a) but during that period discharge problem is the vast quantity of bed load material was quite low and without any significant flash that is transported through Škocjanske Jame flooding, when higher dissolution is expected� during each flood and its destructive influence Therefore we continued with measurements at on the limestone tablets� This was recognized the same location, here named S-1 and S-2� Figure 3.3.1. Position of measurement places from S-1 to S-12 in Škocjanske Jame and on Reka River upward from the caves (source of plan: Archive at IZRK ZRC SAZU). 103 Case Studies - Škocjanske Jame Measurement places S-1 and S-2 were located in the sum of dissolution and corrasion rates is relatively centre of an underground water channel at Swidovo small (on average -1�2 µm/a)� The majority of Razgledišče (Swida’s viewpoint) at the downstream end of weight loss is probably a result of crumbling Hankejev Kanal (Fig. 3.3.1). Only 1.5 m away, a moderate and grinding, which was evidently seen at sum of corrasion and dissolution rates (-20 µm/a) was the limestone tablet located at S-1 (Fig� 3�3�3)� measured with a MEM by Mihevc (2001; 65). Since the Therefore dissolution rates have to be even limestone tablets were placed in the middle of the water smaller, if they exist at all� during the second channel where the velocity of water flow exceeds even and third measurement periods, discharge was 5 m/s and water transports a lot of bed load and suspended quite low� Thus there was only weak mobilization material, a microlocation of measurements was chosen of bed load material and the limestone tablets with great caution to minimize the influence of mechanical showed no corrasional damages� Rates show weak erosion. Measurement points S-1 and S-2 were always under dissolution (-0�2 µm/a) or slight sinter deposition the water when the discharge of the Reka River exceeded (0�8 µm/a)� The highest sum of dissolution and 3 m3/s (on average 58 % of exposure). At each measurement corrasion rates was detected during the fourth place, one limestone tablet was fixed with iron screws, nuts measurement period, which was characterized and felted washers. Misleading dissolution due to iron oxide by two strong flash flood events with discharge seemed to be (almost) absent. Measurements were taken of more than 100 m3/s� Limestone tablets from 1 February 2006 to 10 October 2011 in 5 measurement were strongly damaged due to crumbling and periods. grinding – dissolution rates therefore cannot be determined� The same happened during the The results from measurement points S-1 fifth measurement period but since low water and S-2 are presented in Fig� 3�3�2� in the first conditions also are characteristic for this long of measurement period, several discharges reached a period, average rates are lower in comparison 50 m3/s� Although discharge was quite high, the with the fourth measurement period� in absolute Figure 3.3.2. Dissolution/corrasion and deposition rates at S-1 and S-2 during 5 measurement periods between 1 February 2006 and 10 October 2011 together with average daily discharge (source of hydrological data: Reka discharge data for 2006-2011). 104 Case Studies - Škocjanske Jame terms, corrasion during the fifth measurement where corrasion takes place (polished surfaces, period was 3�1-times higher than during the potholes)� Where it is located at the contact of fourth measurement period due to several floods collapse blocks, the black coating usually sticks with discharges of over 50 m3/s� Nevertheless, collapse material together� This proves that weight loss due to crumbling and grounding sticking of blocks is younger than collapsing or can be taken only in relative terms for corrasion moving of collapsed blocks� The reaction of black rates since limestone tablets are exposed to coating with 10 % solution of HCl is intensive, much higher corrasion than the bed of a channel which indicates calcite (flowstone)� Besides nearby� calcite, 13 % of impurities (weathered flysch rock, due to crumbling and grinding, we were not organic material) were detected with dissolution able to observe dissolution rates at high water of flowstone coating in an HCl solution� if we level at S-1 and S-2� But at least we can say that take into account results from the second and they are very small or even absent if discharge third measurement periods, when the limestone remains under ~50 m3/s� Results from the tablets were not damaged by corrasion, the third measurement period suggest that (sinter) average net sinter deposition rate of 0�3 µm/a deposition is possible during low discharge� could be responsible for at least 3 mm thick From a morphological point of view, three flowstone coating - if we suppose the same rate of different types of surfaces can be recognized in process during the Holocene� Potential thickness the water channel: surfaces with black coating, of flowstone coating corresponds in magnitude polished surfaces as a result of corrasion and to actual thickness� surfaces with scallops as a result of dissolution� The second type of surface, corrasional, is Black coating is several millimetres thick� it developed at places where vast bed load transport is distributed widely in the lower portion of a and whirling takes place� Corrasion rates are very water channel, which is under water at low and different and strongly depend on microlocation, medium discharges� it is absent only at locations as was already measured by Mihevc (2001; 65); Figure 3.3.3. Crumbled and ground edge of limestone tablet at S-1. 105 Case Studies - Škocjanske Jame this is from -20 µm/a at polished surface to collapse blocks in the water channel, which are -160 µm/a at places where bed load is hitting the flooded when discharge exceeds ~10 m3/s� The wall� From our measurements we can conclude morphology of scallops is interesting, since that at several places they are higher than sinter they are long and narrow� The transitional angle deposition rates where they appear� Nevertheless, between scallops is very low, amounting to 75-corrasion can be extremely small in some places, 90º (Slabe 1992; 31)� They form at places with and there sinter deposition prevails� very little corrasion and within a zone between Surfaces with scallops are relatively rare� sinter deposition and back flooding (Fig� 3�3�7)� On the walls, scallops are usually absent� The This statement was tested by measurement of the most characteristic are on the tops of large vertical variability of processes (Chapter 3�3�2)� 3.3.2 Measurement places S-3, S-4, S-5 and S-6, S-7, S-8, and S-9 – vertical variability of processes at Swidovo Razgledišče and at Martelovo Jezero Measurement locations S-1 and S-2 show sinter 1.6 m higher than S-6, S-8 4.5 m higher than S-7 and S-9 deposition at low (and medium) water levels� At 5.5 m above S-8 (12.0 m above geodetic point 58). Limestone high water levels, limestone tablets were altered tablets were replaced and weighed at the same time as S-1 by corrasion� The latter effect overwhelms and S-2 (Chapter 3.3.1). Due to the later establishment of possible dissolution, which is probably the measurement places, overall 3 measurement periods are highest at very high water levels and as such available at Swidovo Razgledišče and 4 measurement also within the focus of our interest� To avoid points at Martelovo Jezero. corrasion, we began to measure with two vertical sets of limestone tablets: at Swidovo Razgledišče Results of measurements from the vertical (Swida’s viewpoint; Fig� 3�3�4; S-3, S-4, and S-5) set at Swidovo Razgledišče are represented in and at Martelovo Jezero (Martel’s lake; S-6, S-7, Fig� 3�3�5� Measurement point S-3, similarly S-8, and S-9)� to S-1 and S-2, suffered from crumbling and grinding� At S-3, corrasion took place during all At Swidovo Razgledišče , water flow can be characterized three measurement periods� Corrasion reduced as supercritical turbulent at low, middle and high water the weight of the limestone tablet at S-3 between levels. At Martelovo Jezero, water flow is slightly less 27 February 2008 and 14 October 2008, which turbulent. During very high discharges, velocity of flow is shows that measurement point S-3 is even reduced significantly at both places since the backflooding more under the influence of corrasion than causes a vast enlargement of the cross-sectional profile of measurement point S-1 or S-2 (compare with water flow. At each of 7 measurement points, 3 limestone measurement period 3 in Fig� 3�3�2)� Corrasion at tablets were exposed to obtain better results. They were S-3 overwhelmed possible dissolution� fixed with stainless steel screws, nuts and felted washers. On the contrary, corrasion was not recognized Measurement point S-3 was fixed only 40 cm from S-2. at measurement points S-4 and S-5� Rates at Measurement point S-4 was located 2.5 m above S-3, while S-4 and S-5 are almost equal, which is most the measurement point S-5 was located 4.9 m above S-3. At probably a result of the rapid rising of water Martelovo Jezero, we were measuring at 4 measurement that flooded both measurement points almost points within a higher vertical span. Measurement point simultaneously, or too weak a difference in rates S-6 was located 0.4 m above geodetic point 58 (located at between two measurement places� during the the shore of Martelovo Jezero) and seemed to be beyond first measurement period, slight sinter deposition the reach of corrasion. Measurement point S-7 was placed (0�7 µm/a) was detected at S-4 and S-5� during the 106 Case Studies - Škocjanske Jame Figure 3.3.4. Cross-section through Hankejev Kanal at Swidovo Razgledišče. Lines on the several tens of metres high right wall are not bedding planes but traces of past flood events. A stalagmite in the water channel is 2 m tall (photo: Borut Lozej, conservationist at Park Škocjanske jame). Figure 3.3.5. Dissolution/corrasion and sinter deposition rates measured at Swidovo Razgledišče between 27 February 2008 and 10 October 2011. 107 Case Studies - Škocjanske Jame second measurement period, slight dissolution at all measurement points� Therefore more can (-0�6 µm/a) was detected� The last and the longest be said about sinter deposition at low discharge measurement period shows slight dissolution and slight or absent dissolution at high water lev- (-0�1 µm/a)� Overal , the average at S-4 and S-5 els� The result of measurements at S-6, S-7, S-8 shows neither dissolution nor sinter deposition� and S-9 (Fig� 3�3�6) confirmed lack of corrasion Weak dissolution rates within measurement at the lowest measurement point� Weight loss in error are surprising since several very big flash one limestone tablet during the first measure-flood events are characteristic for the last two ment period is a result of artificial damage during measurement periods� Results prove that the fixation� Although values are rather smal , evident aggressiveness of the Reka River is very low or transition from net sinter deposition at S-6 toward almost absent even at very high discharge� it is dissolution at higher measurement points can be interesting that suspended material, which is observed� The highest average dissolution rate abundant in water at high discharges, did not (-0�25 µm/a) was detected at S-8, which is located cause visual damage but also did not reduce the 6�1 m above measurement point S-6� upward, dis-weight of limestone tablets� We can assume that solution rates are weaker due to shorter exposure only bed load material is responsible for high times� downward (1�6 m above S-6 at S-7), net corrasion rates detected by Mihevc (2001)� dissolution rates are weaker most probably due to The measurement location of Martelovo Jezero sinter deposition during moments of middle wa-was chosen due to lack of corrasional morphology ter levels� Sinter deposition is even greater at the Figure 3.3.6. Dissolution and sinter deposition rates measured at Martelovo Jezero between 17 April 2007 and 10 October 2011. An artificial y damaged limestone tablet was excluded from the calculated average. 108 Case Studies - Škocjanske Jame lowest limestone tablets (measurement point S-6) 6�5 m) are probably guided by the most aggressive where it prevails over dissolution� during high water but they decrease due to shorter exposure water levels, dissolution also takes place at the times� The morphology of temporarily flooded lowest measurement place, but during middle and passages rarely shows dissolutional features� low discharges, net sinter deposition prevails with More often disintegrated rock surfaces can be 0�44 µm/a� This is similar to the average at S-1 and seen, slightly blurred by dissolution� S-2 (0�3 µm/a; Chapter 3�3�1)� deposition was very Comparison between measured (and obvious during the second measurement period, estimated-mechanical weathering) processes, which was characterized by low discharges� key factors and theoretical features in the inner The results of measurements at Swidovo parts of Škocjanske Jame shows that present-day Razgledišče and Martelovo Jezero demonstrate conditions correspond to the actual present-that we can expect deposition at low water levels day micromorphology of the water passages� and dissolution at high water levels� Change Nevertheless, some features (i�e� scallops) can also from net deposition to net dissolution seems to be inherited from the past and are just sustained occur when the water level in an underground in present-day conditions� Processes, key factors channel rises 1�5 m above low water level (this and features can therefore be summarized in the is at Q ≈ 20 m3/s after Gabrovšek & Peric 2006; general scheme represented in Fig� 3�3�7� 40)� This corresponds to the lower limit of Can we say something about pre-Holocene scallops (Slabe 1992; 32, Slabe 1995; 23), which processes? We already stressed that thickness of are developed at the big col apse blocks in the flowstone coating at the most remote places in water channel out of corrasional locations� At the bottom of the water channel corresponds to higher water level, backflooding prevents the the product of sinter deposition rates and the development of scallops due to the decrease of duration of the Holocene� This indicates that water flow velocity� dissolution rates in upper sinter deposition was absent or at least much portions of the underground channel (above lower than today� As per Gams (1996; 103), Figure 3.3.7. The most relevant present-day processes, factors and features characteristic for Škocjanske Jame. 109 Case Studies - Škocjanske Jame higher aggressiveness of water during ice Ages of weaker biological activity in soils, lower soil can be expected due to frozen ground, which CO2 concentration, weaker dissolution rates promotes superficial runoff without interaction in soil, lower water CO2 concentration at karst with carbonates within the soil� Additional y, springs and higher potential to dissolve rock lower saturation of waters can also be a result underground especial y during high discharges� 3.3.3 Measurement places S-6, S-3, S-10, S-11, and S-12 – longitudinal variability of processes between flysch-limestone contact and Martelovo Jezero Weak dissolution rates in Škocjanske Jame can places S-10 and S-3 (Fig� 3�3�8)� Corrasion was be a result of (a) gradual saturation of the Reka occasional y observed also at S-12 and S-11, River along the more than 7�5 km long water especial y during the second measurement course between the lithological contact flysch- period, when discharges exceeded 100 m3/s, and limestone or (b) already saturated water at the to a lesser extent during the third measurement lithological contact flysch-limestone� Proof for period� one of these two possibilities can be helpful for in the first measurement period, which is understanding the genesis of the limestone gorge characterized by relatively low water levels, de-upstream from Škocjanske Jame and the related position was detected at all measurement points� development of Škocjanske Jame� Therefore deposition rates from the lithological contact we decided to measure chemical processes in a (S-12) remain more or less constant at ~1�2 µm/a longitudinal section from the contact flysch- all the way to Martelovo Jezero (S-6)� Only at limestone to the Martelovo Jezero in Škocjanske the ponor (S-11), are they higher (2�4 µm/a) for Jame� some unknown reason� during high discharge that was characteristic for the second and third Limestone tablets were placed at five different measurement measurement periods, the Reka River seems to points. The farthest upstream (S-12) was located at the be at equilibrium or can display low sinter depo-lithological contact of limestone with flysch, S-11 was located at sition, especial y at Martelovo Jezero� Since sev- the ponor (where the Reka River starts to flow underground), eral limestone tablets were altered by crumbling S-10 was located in the entrance chamber of Škocjanske Jame and grounding it is difficult to say whether dis- (Rudolfova Dvorana; Rudolf’s chamber), while the most solution rates increase or decrease from the con-downstream limestone tablets were located at the previously tact of flysch with limestone� if we compare the described Swidovo Razgledišče (S-3) and Martelovo Jezero average at S-12 (lithological contact) and at S-6 (S-6; Chapter 3.3.2). At each point, measurements were (Martelovo Jezero), sinter deposition rates slight-done using three limestone tablets. They were fixed with ly increase downstream, which proves either (a) stainless steel screws, nuts and felted washers at non or weakly slightly reduced dissolution rates downstream corraded measurement places. All measurement points during high water levels, (b) higher sinter deposi-demonstrate very similar hydraulic conditions – turbulent tion rates downstream during low water levels or supercritical water flow with velocities usual y several m/s. (c) both� Nevertheless, although the Reka River is Results are available for three measurement periods between slightly aggressive at high discharge, average val-2 February 2008 and 10 October 2011. ues at both measurement places show that sinter deposition prevails over dissolution� Net sinter Although limestone tablets were fixed at places deposition rates range between 0�3 and 0�5 µm/a� where the corrasion is supposed to be weak, The main reason for the low aggressiveness corrasion is obvious especial y at measurement of the Reka River in Škocjanske Jame certainly 110 Case Studies - Škocjanske Jame is not the superficial flow of the Reka River over mosphere conditions� Some of them deposit tufa limestone 7�5 km from the ponor; otherwise we in high quantities (e�g� Podstenjšek; Kogovšek could observe at least net dissolution at the litho- 2006) and are highly oversaturated even during logical contact� The reason for the low aggressive- middle discharge� Many tributaries from the Br-ness of the Reka River resides in its catchment kini Mountains decrease the total hardness of the area� The most reliable explanation can be found Reka River (Gams 1962; 278), but they are too in karst springs that feed the Reka River and are weak to substantial y increase the aggressiveness oversaturated with respect to calcite in open at- of the water even at the beginning of flood events� Figure 3.3.8. Dissolution/corrasion and sinter deposition rates measured between flysch-limestone contact (S-12) and Martelovo Jezero (S-6) between 27 February 2008 and 10 October 2011. Crumbled and ground limestone tablets are not included in the calculated average. 111 Case Studies - Škocjanske Jame 3.3.4 Conclusion if we just take into account chemical processes, bottom of the underground channel� The location sinter deposition can be defined as the strongest of such features points out that they were formed geomorphic process in the epiphreatic part of by the whirling of bed load material, while the Škocjanske Jame� The most characteristic is for geomorphic action of suspended load is absent� low discharge� during medium discharge, sinter Rates of corrasion from bed load transport were deposition rates are much lower� According measured by Mihevc (2001)� Measurements and to measurements at Martelovo Jezero and the morphological observations reveal that they can measurement point at the lithological contact be much stronger than sinter deposition and limestone-flysch, net sinter deposition amounts dissolution, but also much weaker at calm places� to 0�3-0�5 µm/a in the lower portions of the water Although the rate of chemical processes is low, channel� Morphologically, sinter deposition present-day processes correspond to present- can be seen as black flowstone coating, which day factors and actual microfeatures along the covers and sticks collapse blocks together in the water course in Škocjanske Jame� Nevertheless, water channel of Škocjanske Jame� The highest the thickness of flowstone cover (several dissolution rate (up to -0�25 µm/a 6 m above the millimetres) shows that the intensity of chemical low water level) appears at high water level, when processes was different before the Holocene� At discharge exceeds about 20 m3/s� dissolution that time, sinter deposition rates were weaker rates most probably rise with higher discharges, or dissolution rates stronger, since we lack but for a very short time� The most problematic thicker flowstone coating� in spite of this, the factor for high dissolution is the time of exposure, deep vertical incision of the meander (Hankejev which is low due to the torrential character of the Kanal) suggests that lateral extension of the Reka River� meander due to dissolution (during low or high About 1�5 m above low water level when water levels) was also weak� This is suggested also discharge is higher than 20 m3/s, slight net by the lack of wall notches, which could form in a dissolution rates become higher than net sinter water channel that is partially blocked by collapse deposition rates� This is also the lowest vertical material or where deepening of a meander point, above which the dissolutional forms can be is slowed by collapse blocks accumulated at observed� The most obvious are scallops, which the bottom of the passage due to mechanical disappear upward because of backflooding and breakdown� dissolutional features of fast water the decrease of flow velocity due to the increase flow at vertical walls are also absent� The most of the cross-sectional area of water flow� Walls probable cause for the incision of the meander is in a flooding zone are characterized by slightly the corrasional activity of water, where bed load dissolutionally blurred primary mechanically material is much more important in comparison weathered rock� Here, slight dissolution due with the action of suspended load� The strongest to flooding is accompanied by condensation geomorphic activity takes place at the bottom dissolution� distinguishing between them is of the water passage and leads more toward usually impossible� corrasional incision than toward dissolutional due to the vast quantity of flysch material lateral extension of the passage� This accounts for transported through Škocjanske Jame, the highly differential characters of Škocjanske corrasional features are well developed on the Jame and Lekinka cave (Chapter 3�2)� 112 3.4 POSTOJNA BASIN-PLANINA POLJE CAVE SYSTEM The drainage between the Postojna basin and the attraction of the cave as a location for tourism Planina polje is completely subterranean and, due began with the discovery of dry and impressively to its explored length and large cross-sectional decorated parts of the cave behind Pivka ponor profile of passages, one of the most important in in 1818, the construction of a single-track under-the dinaric karst� This hydrological y active cave ground railway in 1872 and a double-track under-system is composed of two major caves: Postojna ground railway in 1964 (Gams 2003; 297)� cave system (Reg� No� 747) and Planinska Jama The first scientific research into Postojna cave (Planina cave; Reg� No� 748)� Postojna cave sys- system began with archaeological investigations tem and Planinska Jama together have 27�2 km of the entrance area of Postojnska Jama soon af-of known underground passages – some of them ter the discovery of some of its inner parts� Work are characterized by the underground Pivka River was done by very famous scientists and techni-flow while the other passages are currently dry cians of that time (A� Schaffenrath, H� Freyer, F� (Fig� 3�4�1)� The vast majority of passages are hori- v� Hohenwart, A� Schmidl, F� Kraus, E� A� Mar-zontal and thought to have been formed in epi- tel; for details see Gospodarič 1976; 11-12)� The phreatic conditions by the Pivka River� Planinska latter two were also the first who touched on the Jama is accessible through one entrance that acts question about the speleogenesis of underground as a spring and ends in the upstream direction in passages� Although some work was also done a more than 25 m deep sump (Vrhovec 2000)� Pas- by italians between the First and Second World sages of Postojna cave system connect several en- Wars, a new era of research started with archaeo-trances, from which the cave was explored in the logical investigations (Brodar 1951, Brodar 1966), past and therefore differently named (Postojnska hydrological investigation of the underground Jama, Otoška Jama, Magdalena Jama, Črna Jama, Pivka River (Michler & Hribar 1959), the study Pivka Jama; Fig� 3�4�1)� Some of the listed parts of of wider hydrological conditions between Posto-Postojnska Jama were connected after the First jna, Planina and Cerknica (Gams 1966a) and geo-World War by diving or with artificial tunnels� logical investigations (Pleničar 1961, Šebela 1998) Today, Postojna cave system is famous due to its after the Second World War� The knowledge of having the greatest biodiversity of underground geology and speleology was substantial y deep-species (84 species of troglobionts) in the world ened by Gospodarič (1976), who comprehensively (Culver & Sket 2000; 15)� it is also the type locality studied the whole cave system between Postojna of a number of “first cave” animals, including the basin and Planina polje from the viewpoint of al-first described troglobionts – the beetle Leptodirus lochthonous sediments, speleogenesis and related hochenwarti and the European cave salamander, ages of sediments (1980)� The age of much older Proteus anguinus� (Culver & Sket 2000; 13)� From sediments was studied recently and published by a touristic point of view, Postojna cave system is Zupan Hajna et al� (2008)� The geomorphologic first among all tourist attractions in Slovenia and evolution of the underground passages connected is the most recognized show cave in Europe� The with development of superficial relief was studied 113 Case Studies - Postojna basin-Planina polje cave system by Gams (1965)� Although Postojna cave system is geomorphic evolution and low nearby hydraulic among the most speleological y studied caves in gradients� Planina polje is one of the most typi-the world, the study of speleogenesis is a very hard cal karst poljes of all (a closed depression with a task due to the long multiphase evolution of cave flat bottom, complete karst inflow and outflow, systems� regularly flooded) located on Mesozoic carbon- ate rocks along the dextral strike-slip idrija Geological and geomorphological characteris- fault zone� Between Postojna basin and Planina tics polje, the karst surface on Cretaceous rocks is Postojna cave system and Planinska Jama are lo- characterized by several conical and elongated cated between Postojna basin (~530 m a�s�l�) and hills, which are incorporated within the system Planina polje (~450 m a�s�l�)� Postojna basin is a of elongated (“dry”) valleys and dolines (Gams, closed depression underlain by Eocene siliclas- 1965) – probably a geomorphic modification of tic flysch rocks in the northern part and Creta- tectonic structures� The cave system with under-ceous limestone in the southern part� The relief ground water flow is situated under this karst of Postojna basin is characterized by low gradi- surface with elevations from ~580 m a�s�l� to ents due to mechanically non-resistant flysch ~750 m a�s�l� due to sometimes thin and heavily rocks, relatively tectonically stable long-lasting fractured roofs, several collapse dolines devel- Figure 3.4.1. Plan of cave system between Postojna basin and Planina polje with measurement locations investigated in this study. 114 Case Studies - Postojna basin-Planina polje cave system oped, especially in the area of Postojnska Jama� similar to Senonian – thick-bedded or even non-in Pivka Jama and Črna Jama, collapsing formed bedded� Lower Turonian limestone is usually a new entrance to the cave system� characterized by thinner layers and can be rich The general geological structure of the karst with up to a decimetre thick layer of chert� The massif where Postojna cave system and Planins- consequence of chert in Lower Turonian lime-ka Jama are located is very simple� it is composed stone is higher occurrence of pipe flow� of upper and Lower Cretaceous limestone, Cenomanian limestone (K 12) is non-bedded which are folded due to compression in a SW- and can be reached just at the downstream end NE direction (Fig� 9�4�2)� The farthest SW fold is of Pivka Jama and in a dry passage called Paradiž the Postojna anticline, in which the majority of (paradise) in Planinska Jama� The non-bedded passages of Postojna cave system are developed� structure of this limestone is most probably re-To the northeast, the Studeno syncline is devel- sponsible for the development of deep sumps be-oped, where the downstream passages of Posto- tween Postojna cave system and Planinska Jama, jna cave system and the unexplored connection although some short passages with free-surface with Planinska Jama are formed (Gospodarič flow exist in them (Vrhovec 2000)� Almost all 1976; 21)� Water flow between Pivka basin and passages of Planinska Jama are formed in Low-Planina polje crosses the folded structure in a er Cretaceous limestone (K1, Gospodarič 1976)� perpendicular direction and therefore crosses Lower Cretaceous limestone can be thick-bed-the same lithostratigraphic units several times� ded or thin-bedded� They contain layers of dolo-The whole karst massif is dissected with several mite and brecciated limestone� At the transition tectonic structures in NE-SW and NW-SE direc- with Cenomanian strata, layers of chert can be tions (Čar & Gospodarič 1984, Šebela 1998) but found� Passages that are developed in limestone none of them alter significantly the general pat- with chert are smaller� tern of the folded structure� At the contact with The cave system between Postojna basin and Eocene flysch rocks (E1,2), the dip of the strata Planina polje is comprised of at least two almost can be almost vertical but elsewhere is usually horizontal levels that can be uniform in some less than 45 º� cases (Veliki dom in Postojnska Jama, the ma- The youngest rocks, in which the entrance jority of passages in Planinska Jama)� The upper parts of the Postojnska Jama and Pivka Jama pas- level is dry and only the lower one is hydrologi-sages are developed, are Senonian layers (K 32), cally active� The drainage pattern between Pos-which are developed as thick-bedded limestone� tojna basin and Planina polje also changed lat-The upper layers of Turonian limestone (K 22) are erally, which results in several passages being at Figure 3.4.2. General geological SW-NE cross-section between Postojna basin and Planina polje with position of Postojna cave system and Planinska Jama (modified after Gospodarič 1976; 25). 115 Case Studies - Postojna basin-Planina polje cave system the same elevation� At the same time, cave pas- system and Planinska Jama was confirmed by sages have been developed under the influence of several tracing tests� vertical percolation and the underground water The Pivka River originates from a karst spring flow of Pivka River� Gospodarič (1976; 15) states located 16 km south of the entrance to Postojna that different parts of the cave system were influ- cave system� during middle and high water lev-enced by very different speleogenetic processes els, several karst springs, mainly from the east and factors often at the same time and that many (the Javorniki Mountains), feed the superficial erosion-accumulation phases even within in- Pivka River course� Tributaries from the western dividual passages occurred as well� At present, side are also numerous but relatively small� Their even such abundant knowledge regarding Posto- catchment area extends mainly over siliciclastic jna cave system and Planinska Jama, which was flysch rocks� during middle water levels, dis-accumulated by Gospodarič (1968, 1976), and charge of Pivka River at the lithological contact later deepend by others (i�e� Zupan Hajna et al� limestone-flysch (11 km downstream from the (2008), is insufficient for a temporal and spatial source) amounts to 2�86 m3/s (Kolbezen & Pris-speleogenetic interpretation of the whole cave tov 1998)� during low water levels, all the water system� from the upper Postojna basin, which is made up The present-day dissolution rates of the Pivka of Cretaceous limestone, flows underground to-River were measured only by Gams (1966b; 35)� ward Malni springs and Planinska Jama (Habič Although he strongly supported the idea of dis- 1989; 240)� during high water levels, discharge solutional formation of passages along the un- reaches up to 26�4 m3/s (Kolbezen & Pristov derground Pivka River, his measurements only 1998) due to the rise of a piezometric surface un-partially confirmed his expectations; his hydro- der the Javorniki Mountains and therefore abun-chemical measurements between the entrance to dant karst springs below them� Postojnska Jama and Spodnji Tartar (the lower Between lithological contact limestone-flysch Tartarus) confirmed a downstream increase of and the ponor of the Pivka River, the most impor-hardness in just 11 cases while in about 14 cases tant tributary of the Pivka River is the Nanoščica he found either no evidence of an increase or River, which contributes 1�41 m3/s during middle even a decrease of hardness� in addition, down- water levels and up to 15�9 m3/s during high water stream increase of hardness was almost always levels (Kolbezen & Pristov 1998)� The catchment within or very close to the range of error� Low area of the Nanoščica River extends over the low-rates were confirmed also with further measure- er Postojna basin, which is formed by siliciclastic ments with three limestone tablets made in the flysch rocks� Therefore the Nanoščica River is fed entrance area of Postojnska Jama (Gams 1996)� mainly by superficial runoff� However, it is also due to such low rates, Gams was not able to pro- fed by several small karst springs under Nanos vide absolute dissolution rates� downstream, the Mountains and from the karst spring Korentan, aggressiveness of the underground Pivka River which drains the partly isolated karst of Orehek all the way to Planina polje is unknown� (Gospodarič et al� 1970, Petrič & Šebela 2004)� Only 2�3 km downstream from the confluence Hydrological characteristics of the Pivka and Nanoščica Rivers, the ponor of The hydrological backbone of the Postojna cave the Pivka River is situated at 511�5 m a�s�l – sev-system and Planinska Jama is the Pivka River, eral metres below the dry entrance to Postojnska which joins the underground Rak River in Pla- Jama� The lowest discharge is characteristic for ninska Jama� Together they are called the unica summer months when it amounts to several tens River, which flows through Planina polje� This of l/s� High water level is characteristic for the hydrological connection between Postojna cave late autumn and spring months� in the case of 116 Case Studies - Postojna basin-Planina polje cave system long-lasting intensive precipitation, discharge up (Perko’s passage)� it is possible that they are ac-to 65 m3/s can appear (Habe 1966; 50)� in such tive only during higher water levels and dry up cases, a large portion of free-surface flow in Pos- during low water levels� The next two tributar-tojna cave system turns to pipe flow, yet without ies were observed only by divers since they are significant damming� The most intensive dam- located downstream from the downstream sump ming occurs at rare narrow places (e�g� in Mag- of Pivka Jama� The first one could be the under-dalena Jama) and in some collapse chambers (e�g� ground water flow of superficial streams sinking Martelova dvorana; Martel’s chamber)� There- north of the Postojna cave system and Planinska fore, the general gradient between the ponor of Jama (Vrhovec 2000; 167)� The second tributary the Pivka River in Postojna cave system and the is very strong (estimated at 20 % of the Pivka spring of the unica River from Planinska Jama River, Vrhovec 2000; 168) and should have its (455 m a�s�l�) amounts to 10�6 ‰ (d = 5�3 km; catchment area at the Javorniki Mountains or in ΔH = 56 m)� the upper Pivka basin, since some tracing tests Water flow in the Postojna cave system and confirmed the connection of these areas via an Planinska Jama is influenced by a water gradient unexplored passage between Pivka Jama and the that is perpendicular to strata dip and the main Pivka branch in Planinska Jama (Habič 1989, tectonic structures (crushed zones, Šušteršič et Kogovšek 1999; 184-185)� Further downstream, al� 2001), and all this obstructed unidirectional where an unexplored connection between Posto-water flows toward Planina polje� Water flow is of jna cave system and Planinska Jama is located, a zigzag character since water chooses the most we can also expect tributaries from the northern effective way through widened bedding planes area, where some sinking streams from flysch and faults/cracks� Where the underground Piv- rocks near Studeno are located� The latter can ka River flows along strike, free surface flow in flow toward Vipava spring as well, but such con-subhorizontal passages is developed� Water pas- ditions are less probable� in Planinska Jama, the sages are usually more than 10 m wide and more Pivka River receives the strongest tributary – the than 5 m high� A challenge for underground Rak River� The hydrogeological characteristics of water flow is a flow perpendicular to strata dip the latter are even more diverse than the hydro- (Pleničar 1961), which is often accompanied by geology of the Pivka River� several sumps often acting as restrictions� The The Postojna cave system and Planinska Jama bed of a water channel is usually covered with drains the area of Postojna basin, which is quite collapse material and allochthonous flysch mate- densely populated, without tertiary treatment rial, consisting mainly of clay and silt, sand and of waste water and sometimes with runoff wa-pebbles being less common (Kranjc 1989; 65)� ter of strong agricultural influence� Biologically Along the underground flow of the Pivka decomposed organic matter in water treatment River, several tributaries are recognized, both plants or in the water channels highly increase visually (Michler & Hribar 1959, Gams 1966a) the natural background of dissoluted salts in and through tracing tests (Habič 1989, Kogovšek water which can influence dissolution (or sinter) 1999)� The first one is the underground Črni Po- deposition rates� tok, which joins the underground Pivka River in Otoška Jama from the left side through the Le- Meteorological characteristics kinka cave (see Fig� 3�4�1)� The next three right due to the many entrances to Postojna cave tributaries were recognized by Michler (1959) in system, the latter is very well ventilated (Gams Magdalena Jama but not by Gams (1966a), who 1970)� Only smaller passages close to the sumps observed another weak tributary (Q ≈ 1 l/s at are less ventilated, while the majority of water low water level) of vadose water in Perkov Rov passages are characterized by intensive air flows 117 Case Studies - Postojna basin-Planina polje cave system (e�g� between the entrance to Postojnska Jama all entrance, which enables two contrary wind di-the way to the Magdalena Jama, the entrance part rections in vertical cross-section� inner passages of Pivka Jama)� Therefore, CO (above the confluence of the Pivka and Rak Rivers) 2 concentration is relatively low even during summer months are less ventilated, especially the Pivka branch� (Gams 1974; Šebela et al� 2012)� The latter statement was confirmed through CO2 On the contrary, Planinska Jama is well ven- concentrations, which were relatively high even tilated only in the entrance zone due to its large at the end of winter (~1,500 ppm)� 3.4.1 Measurement location P-1 – temporal and vertical variability of processes in the entrance area of Postojna cave system The first research that considered dissolution rates This vertical arrangement was used to obtain insight into the in Postojna cave system was by Gams (1966b; 35)� vertical variability of processes and to evaluate the influence Several times he observed differences in water of different discharges within 78 cm of the high measurement hardness between Veliki dom (big chamber) and zone. At the lower position (HVeliki dom = 0 cm), three limestone Spodnji Tartar (lower Tartar)� Most often these tablets were instal ed instead of one to obtain better occur at low water levels between January and precision for longitudinal comparison of karst processes rates March, when the majority of water comes from (Chapter 3.4.2). These limestone tablets were always under the Nanoščica River and the portion of the Pivka the water, while the upper tablets were temporarily above the River is smal � Later, Gams (1996) measured water level. The limestone tablets were fixed with stainless steel cumulative dissolution rates using three screws, nuts and felted washers to avoid any influence of iron limestone tablets placed in the Pivka River in oxides. Due to the width of the chamber, water flow can be Veliki dom (the entrance chamber of Postojnska defined as low turbulent and subcritical at low and middle Jama)� His results show that dissolution rates are discharges. At high discharge, water flow is characterized extremely low, if they exist at al � He was not able by large eddies. During very high discharge, backflooding of to provide exact values� 7-8 m results in lower velocity of water flow (~0.5 m/s). Our first observation was done with two lime- At the end of the measurement, results for four measure- stone tablets during a test study close to Gams’ ment periods were available. In the last measurement periods, (1966b, 1996) measurement location in Veliki the lowest limestone tablets were damaged by floating debris dom (Chapter 2�2�2)� unfortunately, the lower and washed away during extremely high water levels. limestone tablet was broken due to the trans- port load of the Pivka River� About 1 m higher Results for four measurement periods and for a limestone tablet indicated slight dissolution the average are presented in Fig� 3�4�4� Although (-0�1 µm/a)� in 2007 we continued with measure- we cannot reliably calculate the average for the ments at a more appropriate location (measure- two lowest measurement locations, the average is ment location P-1), which is less influenced by certainly positive with values up to ~1 µm/a� This the bed load sediments of the Pivka River� means that up to HVeliki dom = 30 cm dissolution is absent on average (it can exist occasional y but is Measurement location P-1 was located about 150 m exceeded by deposition)� Above, dissolution is the downstream of the ponor of the Pivka River in Veliki Dom highest at HVeliki dom = 60 cm where amounts were on the right side of the underground Pivka River. The whole -0�6 µm/a� An upward weakening of dissolution set of 16 limestone tablets was arranged on a metal bar in rates is expected but cannot be confirmed within an oblique position (Fig. 3.4.3), where the vertical distance a 78 cm high measurement zone due to slight and between the centres of the limestone tablets amounted to 6 cm. therefore unreliable differences� Transition from 118 Case Studies - Postojna basin-Planina polje cave system Figure 3.4.3. Limestone tablets at measurement location P-1 in Veliki Dom in Postojnska Jama during low water level. Figure 3.4.4. Dissolution and deposition rates in four measurement periods and average periods between 26 September 2007 and 24 August 2011 at measurement location P-1. 119 Case Studies - Postojna basin-Planina polje cave system deposition into dissolution is gradual and can findings of Gams (1966b; 35)� during low water be described very well up to 78 cm high with a levels, deposition prevails� Corrasion should not logarithmic curve since R2 amounts to 0�77� be seen as an important process since the biggest A detailed view into individual measurement weight loss is not related to the lowest limestone periods displays a much more diverse situation tablets� in comparison with average values� during the during the second measurement period, first measurement period, water most probably the portion of the Nanoščica River was small flooded all limestone tablets (Fig� 3�4�5)� The during higher discharges� Additional y, the water transition from moderate deposition into level was quite low in the second part of the dissolution is gradual� At HVeliki dom = 70 cm measurement period (summer 2008) when the dissolution diminishes since the highest water waters of the Nanoščica River strongly prevailed� level reached the upper limestone tablets for a As a result, deposition prevailed over dissolution very short time� during such autumn and winter at all vertical zones� The highest deposition rate peak discharge at least the initial contribution was characteristic for the lowest limestone tablets of the Nanoščica River is important due to fast where amounts were almost 10 µm/a� At least superficial runoff from the nearby area covered a small portion of weight gain (this indicates by flysch rocks, while later it is followed by the deposition) can be contributed to the organics prevailing runoff from the karst area (Habe 1966; deposited especial y on the lowest limestone 50)� dissolution was detected during autumn tablets (pol ution) which could not be adequately and winter months, which corresponds to the removed from the tablets’ surfaces� Figure 3.4.5. Water level, portion of the Nanoščica River and average dissolution/deposition rates at measurement location P-1 during four measurement periods between 26 September 2007 and 24 August 2011. Red arrows show the ten highest culminations of the high portion of the Nanoščica River and high water level in front of Postojnska Jama. The rise of the water level presented in this figure fits quite well with the rise of water at measurement location P-1. 120 Case Studies - Postojna basin-Planina polje cave system One of the highest discharges was characteristic load material� Nevertheless, corrasion was only for the third measurement period, when water strong enough to remove part of the relatively flooded all the limestone tablets for several soft organic material, while the limestone tablets meters (Fig� 3�4�6)� At such a high water level, remained visual y uncorraded� which is usual y also long lasting, the discharge The fourth measurement period was of the Pivka River strongly prevails over that of characterized by very low and very high the Nanoščica River� This is the reason for the low discharges during which the Nanoščica River dissolution rates that were detected only at the top contributed an important portion of water of the vertical zone at value -0�2 µm/a� This is even (Fig� 3�4�5)� unfortunately, long measurement lower than during much lower water levels from periods average extreme events� One of them the first measurement period� The hydrological was a flood in September 2010, which was situation during the third measurement period exceptional since it was the second highest in the confirms that the most important factor for high last 100 years (Šebela 2010); it was general y an dissolution rates is not just discharge but also the effect of the prevailing portion of the Pivka River� portion of the more aggressive Nanoščica River in Average values (Fig� 3�4�5) and individual values the sinking stream� The lowest two measurement at specific measurement points at measurement points at measurement location P-1 could location P-1 (Fig� 3�4�4) were the lowest observed indicate weak corrasion from the side of bed ever� At all vertical zones dissolution prevails over Figure 3.4.6. Flood in Veliki Dom (entrance chamber of Postojnska Jama) on 12 December 2008. Measurement location P-1 is located at the arrow about 8 m below the water level (photo: Mitja Prelovšek). 121 Case Studies - Postojna basin-Planina polje cave system deposition with an average value of -0�7 µm/a� high portion of the Nanoščica River and high Nevertheless, if we take into account that water level in the front of Postojnska Jama in the circumstances were in favour of high dissolution whole measurement time span), the latter are rates (7 of the 10 highest culminations of the still small� 3.4.2 Measurement locations P-1, P-2, P-3, P-4, P-5, P-6, P-7, and P-8 – temporal and longitudinal variability of processes along underground water flow from Postojna basin to Planina polje underground water flow of the Pivka and The average rates of processes can be unica Rivers (downstream from the confluence calculated only for measurement locations where with the Rak River) is more than 10 km long� all the results are available� These are, namely, Since for non-divers the inaccessible distance P-2 (Spodnji Tartar) and P-5 (Pivka Jama)� in between terminal sumps in Pivka Jama and both cases deposition prevails over dissolution Planinska Jama amounts to only ~1�5 km, already but is significantly reduced away from the ponor explored passages with numerous accesses to the (from 1�1 to 0�1 µm/a)� deposition in Spodnji underground flow provide us with an excellent Tartar can be related to biogenic film (organic opportunity to measure the rate of processes all material), which appears as a black coating on along the underground water flow� The latter is the limestone tablets� Growth of biogenic film is crucial for studying the hydrological connection enhanced by pol utants that contain nutrients – between the Pivka basin and Planina polje and concentration of the latter substantial y decreases therefore indirectly dictates the geomorphological from the entrance to Postojnska Jama to Pivka evolution of both depressions� Jama (Sket & Velkavrh 1980)� Therefore, at least a portion of decreased deposition rates between The rate of dissolution or deposition was measured at Spodnji Tartar (P-2) and Pivka Jama (P-5) can be eight measurement locations along the underground water attributed to decreased growth of organic film� course (Fig. 3.4.1). The upper one (P-1) was located 150 m Fig� 3�4�7 reveals some differences between from the entrance to Postojnska Jama and the lowest one measurement periods� General y speaking, 175 m upstream from the entrance to Planinska Jama. All during all measurement periods a gradual measurement locations were placed at a similar depth and decrease of deposition rates is characteristic were under the water even during low water levels. The most between Veliki dom (P-1) and Pivka Jama (P-3, evident difference between them is the velocity of water flow, P-4 and P-5)� Further downstream, deposition which was the lowest at measurement locations P-1 and becomes stagnant or gradual y increases again� P-5 and the highest at P-3, P-2 and P-6. At all locations, The highest deposition (and later decrease) measurements were done using three limestone tablets at the was detected in the entrance part of Postojnska same time for better precision. Limestone tablets were fixed on Jama, especial y during the second measurement stainless steel screws, nuts and felted washers. period� The latter period lasted over the At P-1, P-2, P-3, P-4, P-5 and P-8, measurement started summer when discharges were lower and water on 26 September 2007 or before while at P-6 and P-7, temperatures higher� The accumulation of measurement started on 19 February 2008. Due to some biogenic film on the limestone tablets at P-1 and troubles (crumbling/grinding, washing away, uncompleted P-2 was visual y obvious in the cave and was later gathering of tablets), results are not always available for all incorporated into weight gain since it was not four measurement periods. possible to remove it completely before weighing the tablets� Much lower values of deposition 122 Case Studies - Postojna basin-Planina polje cave system were characteristic for the autumn and winter underground water flow and from the Javorniki months during the first and third measurement Mountains, a constant pH value can be sustained periods� during the fourth measurement period, only by sinter deposition� This conclusion should the deposition rate at P-2 amounts to 0�6 µm/a, be verified in the future, but up to now it gives higher than expected at P-1 (see Fig� 3�4�4) and us the most reliable explanation for increasing also higher in comparison with measurement deposition rates along the Pivka River in locations P-3 and P-5, where slight dissolution Planinska Jama� was detected (-0�2 µm/a)� Along the underground Pivka and unica Riv- in Planinska Jama more than 7 km from the ers, passages have been formed along faults and ponor of the Pivka River, the deposition of biogenic tectonical y deformed bedding planes (Šebela film was not visual y observed on limestone 1998; 78)� A strong prevalence of breakdown tablets but deposition remained� The deposition morphology is therefore expected, but according rate increases constantly and unequivocal y from to our results it can be dissolutional y modified P-6 (0�8 µm/a), to P-7 (0�9 µm/a) to P-8 (1�1 µm/a)� on the ceiling and depositional y modified at the Highly sensitive pH measurements from P-6 and bottom of the water channel� The most evident P-8 showed a constant pH value (8�07-8�09)� if dissolutional features along the underground wa-we take into account that we detected outgassing ter course of the Pivka River are scallops, which of CO2 in front of Planinska Jama and that form during fast water flow, where dissolution-outgassing of CO2 can also be expected along the al y widened cracks and poorly developed box-underground Pivka River in Planinska Jama due work exist, formed initial y when the water flow to the contribution of autogenic recharge along was relatively slow� The formation of all dissolu- Figure 3.4.7. Dissolution/deposition rates during four measurement periods between Postojna basin and Planina polje (in Postojna cave system and Planinska Jama) between 26 September 2007 and 24 August 2011. Due to some missing data, average dissolution/deposition rates are only calculated for P-2 and P-5. 123 Case Studies - Postojna basin-Planina polje cave system Figure 3.4.8. Dissolutional morphology and limestone tablets at P-5 (Pivka Jama). TD Diver for measuring water level and temperature was used by Janez Turk. tional features can be explained by present-day are observed in the lower portion of the water processes, but for the formation of the whole channel (Fig� 3�4�9) cannot be formed by present-feature, several tens of thousands of years are day processes (present-day chemical processes needed� in Planinska Jama, the absence or at least are able to preserve them but not to renew them) very weak dissolution is proven also by the many and are therefore inherited from the past when thin and fragile carbonate cave snail shel s that the chemical characteristics of the water were dif-are deposited on the banks and cannot be dis- ferent� This is also evident from the smoothened solved by the Pivka or unica Rivers� Features that transitions between scallops (Fig� 3�4�9)� 3.4.3 Measurement locations P-7, P-8 and C-7 – measurement of mixing corrosion at underground confluence of Pivka River and Rak River The confluence of the Pivka River and the Rak River temperature and related chemical parameters is one of the biggest underground confluences in are also different, which can lead to mixing the world� At a specific hydrological situation corrosion� At high discharge, the hydrological (middle-low discharges), both streams that situation is much more complex – both rivers are join at Sotočje (confluence) have very different fed by diffuse autogenic, concentrated autogenic catchment areas; the Pivka River drains mostly and allogenic recharge� allogenic waters from the northern Pivka basin while the Rak River drains the autogenical y To observe possible dissolution due to mixing, three recharged water of the Javorniki Mountains� measurement locations were used. Measurement location P-7 during winter and summer months water was located in the underground Pivka River, C-7 in the Rak 124 Case Studies - Postojna basin-Planina polje cave system River and P-8 300 m downstream from the confluence in the confluence in the unica River� it is worthy of note underground Unica River where waters were well mixed. At that the same succession was observed during the each measurement location three limestone tablets were used second and third measurement periods� during at the same time to obtain more precise data. All limestone the third measurement period, slight dissolution tablets were placed in very similar hydrological conditions; in the range of average error was observed in they were flooded at low and high water levels and dry only at the Rak River� during the second measurement very low water levels. The water flow can be characterized as period, which was characterized by low turbulent and subcritical; only at C-7, given a higher velocity discharges especial y in the second part of the can the flow be characterized as supercritical. Limestone measurement period (Fig� 3�4�5), the rates in the tablets were fixed with stainless steel screws, nuts and felted Pivka River were similar to those in the Rak River washers. although the catchment areas were characterized Measurement at P-8 began on 26 September 2007, on P-7 by various types of recharge� and C-7 on 19 February 2008. Therefore, only data from 19 instead of possible dissolution or the lowest February 2008 till 26 March 2009 (end of measurements) sinter deposition due to mixing, the highest sinter were used for evaluation. deposition rates were observed downstream from the confluence at P-8� A possible explanation is Results are presented in Tab� 3�4�1� On average, that outgassing of CO2 from the water, which is all measurement locations indicate deposition, the highest downstream of the confluence due which, due to the absence of black organic coating, to the nearness of the well ventilated entrance to is thought to be sinter deposition� The lowest rates Planinska Jama, prevails over mixing� if mixing were observed in the Rak River (C-7), where the dissolution (or lower sinter deposition) occurs, it average rate corresponds to rates at Malni springs is limited to several tens of meters downstream and in Tkalca Jama located upstream (Prelovšek from the confluence where measurements are 2009)� deposition is slightly higher at P-7 difficult to perform due to a spatial y extensive (Pivka River) and the highest downstream from zone of mixing� Table 3.4.1. Dissolution or deposition rates (µm/a) at the underground confluence of the Pivka River and the Rak River between 19 February 2008 and 26 March 2009. P-7 (Pivka River) C-7 (Rak River) P-8 (Unica River) First measurement period / / 0�8 Second measurement period 1�2 1�1 1�5 Third measurement period 0�4 -0�1 0�5 AVERAGE 0.9 0.6 1.1 125 Case Studies - Postojna basin-Planina polje cave system 3.4.4 Conclusion The cave system between Postojna basin dissolution is characteristic for the upper and Planina polje (Postojna cave system and portion of water passages and can (on average) Planinska Jama) connects two extensive amount in the entrance part of Postojnska Jama closed depressions� The relationship between up to -0�6 µm/a� The strongest dissolution rates depressions and cave systems is bidirectional – were detected during the fourth measurement the cave system provides a drainage system for period (-1 µm/a) when the Nanoščica River the basins but conditions in basins influence cave prevailed at least at the rising limb of high water system genesis� levels� On average, vertical net transition from The lowest and therefore hydrologically net deposition to net dissolution occurs when active passages of this cave system are currently water rises by about 30 cm above the low water influenced by the Pivka River� The latter level in Veliki dom� (downstream from the confluence with the Although several tributaries with different Nanoščica River) shifts from undersaturated water characteristics join the underground Pivka during high water levels (in cases when River (the strongest one being the Rak River in the Nanoščica River strongly prevails) to Planinska Jama), rates of chemical processes are oversaturated when the water level is low� in the not influenced much� Results from Planinska case of high water levels and a small portion of Jama show that theoretic mixing dissolution the Nanoščica River, the dissolution rate is absent is overshadowed by outgassing of CO2 from or too low to be reliably detected with limestone the water� Consequentially, even higher sinter tablets (under -0�1 µm/a)� Since both processes deposition is characteristic for measurement overlap, especially in the lower parts of water locations downstream of the confluence� passages, we should speak about net deposition Although the prevailing morphology of rates instead of deposition rates since net rates hydrologically active passages indicates a are composed of deposition during low water strong influence of collapsing, some parts of levels and occasional dissolution during high the passages show (epi)phreatic dissolutional water levels� The shortest and the most extreme morphology� Present-day processes support the the measurement period is, the most extreme the formation of such morphology only in the upper rates are to be expected� parts of the water passages over longer periods The main chemical net process in the lower of time (several tens of thousands of years)� portion of water passages is net (sinter) deposition due to prevailing deposition, the formation of that on average amounts 1�1 to 0�1 µm/a� it is dissolutional morphology in the lower parts of higher in the entrance part of Postojna cave water passages is not possible and present-day system and Planinska Jama� The middle part of features at such locations have to have been the underground system (Pivka Jama) indicates inherited from the past� One possible period for lower net deposition rates (0�5 µm/a) due to their formation is during a colder climate, when lower deposition rates during low-middle water a higher percentage of superficial runoff and levels� in shorter measurement periods (if only lower CO2 concentration in diffuse autogenic summer low water levels are taken into account recharged water would certainly support higher – e�g�, during the second measurement period) aggressiveness of the water that sinks into net deposition rates can be up to 10 µm/a high� Postojnska Jama� 126 GENERAL 4 CONCLUSIONS, DISCUSSION AND POTENTIAL FOR FURTHER RESEARCH 4.1 Methodology Measurements of karst processes require the use The biggest advantage of measuring with of special techniques, among which the use of limestone tablets is their high precision (up micrometer (MEM), hydrochemical methods, to ±0�05 µm) and accuracy (on average ±0�2 µm; and limestone tablets are the most widely known� maximum error ±0�4 µm) if we dry them in The MEM provides the most direct way to observe a desiccator and oven or if we use a correction surface lowering or rising and is therefore the equation to reduce the influence of relative most relevant methodology for defining absolute humidity� Another advantage is having the ability rates of processes at specific locations� However, to compare dissolution or sinter deposition rates the influence of error increases with decreasing regardless of lithological differences between rates or with frequent MEM measurements� measurement locations (e�g� caves)� The latter can Since the rate of chemical processes on the karst be a problem if we are interested in absolute rates is usually low, the effective use of a micrometer at a specific measurement location in the cave, is limited to places with exceptionally strong especially if net sinter deposition is observed dissolution rates or where several years are or the lithology at the measurement location is available for single measurements� much different in comparison with standard in specific situations, the highest accuracy can limestone tablets (in our case in Križna Jama)� be achieved through hydrochemical analysis; for if we are observing net dissolution rates, the example, if a cave stream extends over several naturalization of the limestone tablet’s surface hundreds of meters without tributaries and the can be achieved with exposure to a measurement reaction surface is known� These conditions are location for an assumed period when about hard to come by, though� The hydrochemical 25 µm of the limestone tablet’s surface is method averages rates over several hundreds of dissolved� Limestone tablets should be fixed meters, which can be problematic at places where with non-oxidizing and non-abrasive material microlocal changes occur due to different flow like stainless steel (inox) or plastic (PVC)� velocities (in our cases in Križna Jama and in Shorter intervals of measurements reduce the Lekinka cave)� influence of cave microorganisms, which can The use of limestone tablets is a site-specific play a significant role at weak dissolution rates methodology and from this perspective falls but require stable living conditions, which are between the MEM and hydrochemical methods� significantly changed with short measurement 127 General Conclusions, Discussion and Potential for Further Research intervals when the limestone tablets are dried� are easier to transport)� At least in the Slovene A similar poorly understood influence is caused (Prelovšek 2009) and Australian stream caves by washing out the deposited fine-grained (Spate et al� 1985) where precise measurements sediment� At places with high corrasion rates, were already taken, rates of chemical processes the use of limestone tablets yields irrelevant are usually so low that use of limestone tablets results; a MEM is better – although, in such cases is practically the only suitable methodology we are not measuring just dissolution rates but for defining dissolution or sinter deposition a spatially highly changeable sum of dissolution rates within several years� Some additional and corrasion rates� The use of limestone tablets is experiences with limestone tablets are needed the simplest one in the field since it requires only to confirm the suitability of this methodology limestone tablets, screws, nuts and felt washers for correct absolute (at least net dissolution) for fixation and some standard equipment for rates� Although we took some measurements, single rope technique (i�e� a drill)� Preparation of additional work can be done with contemporary limestone tablets can be done in a laboratory� measurements over shorter and longer intervals To conclude, the use of appropriate to evaluate the role of cave microorganisms methodology for measurements depends mainly and clay/silt sedimentation in dissolution on rates of processes, presence of corrasion, goals and sinter deposition� Additional comparable of measurements (absolute vs� relative rates) measurements with limestone tablets and a and accessibility of passages (limestone tablets MEM would also be beneficial� 4.2 Rates of dissolution/sinter deposition it is hard to simplify and average underground at the surface� From the Slovene perspective dissolution or sinter deposition rates in stream it is interesting that the aggressiveness of the caves since they depend on many factors besides main karst streams was denied by Oertly’s discharge� This is the reason for very different hydrochemical measurements, a questionable directions and rates of processes evident at matter for Melik (1955) and generally accepted the same time (Fig� 4�1)� For nearly all case by Gams� it is possible that net dissolution takes studies (the only exception might be Lekinka place in weakly or non-aerated passages but such cave), chemical processes are bidirectional in passages can be accessed only by divers� Several the bed of a water channel� This means that at decimetres or metres above the bed of a channel, the same measurement locations, dissolution only (net) dissolution can be expected� and sinter deposition was detected during a in general, annual dissolution or sinter year, a circumstance confirmed in other caves deposition rates in stream caves are low, which (Palmer 2007)� if cumulative rates are measured corresponds to the notion of the long-term over longer periods, net rates depend on the evolution of individual passages� Along the intensity and duration of dissolution and sinter most known cave streams (e�g� Škocjanske Jame, deposition rates� it is somehow surprising that Postojna-Planina cave system and Cerknica-net dissolution prevails over net deposition Planina polje cave system (Prelovšek 2009 and only in Lekinka� This is a result of the origin of non-published data)), rates weaker than μm/a are the water that derives from diffuse infiltration common� Such rates are characteristic for caves through soil and the vadose zone and becomes influenced by diffuse autogenic recharge, mixed oversaturated due to the outgassing of CO2 autogenic-allogenic recharge and even allogenic from the water at well ventilated passages and recharge, where a sinking stream at least partly 128 General Conclusions, Discussion and Potential for Further Research s. tudie ase sn c ined ibta ocations o ent l easurem acteristic mar ost ch he mt t sition a epo inter d nd s issolution af d ourse oal cpor .1. Tem ure 4Fig 129 General Conclusions, Discussion and Potential for Further Research drains the catchment area underlain by carbonate 17�0 µm/15 days (413�7 µm/a for comparison) for rocks� in the case of Škocjanske Jame calcite sinter deposition rates� Even stronger rates are to precipitates from the water already at the contact be expected if the rates are measured in shorter between siliciclastic flysch rocks and limestone intervals - i�e�, per week, per day or per hour� and the same process with similar rates continues Temporal variability was already discussed in the underground Reka River� Nevertheless, in the previous paragraph� We could expect dissolution rates a magnitude higher are expected that sinter deposition is characteristic for lower during hundreds of thousands (even of a million discharge and dissolution for higher discharge� or more) of years since (a) present-day sinter But since discharge is not the only factor, we deposition rates do not result in dissolutional can only say that sinter deposition cannot take enlargement of beds of passages (Križna Jama- place during high discharge and, aside from in Križna Jama 2 cave system, Škocjanske Jame, Križna Jama-Križna Jama 2 and Lekinka cave, Postojna-Planina cave system) or (b) dissolution dissolution cannot take place during low water rates during suitable conditions are too low levels� Other important factors that influence to produce an actual cross-sectional profile of direction and intensity of rates are origin of water passages in several millions of years� Shift from and seasonal changes of soil CO2 concentration (a) prevailing sinter deposition to dissolution or or seasonal changes in ventilation� usual y, the (b) from weak dissolution to stronger dissolution highest dissolution and sinter deposition rates rates, can be achieved with climate changes or do not depend on the highest or the lowest changes of hydrological systems� The thickness discharge� Only in the case of Škocjanske Jame, of flowstone coating in Škocjanske Jame and were the highest dissolution rates observed in Križna Jama suggests that annual net sinter during the highest water levels and it seems that deposition rates are characteristic for the the highest sinter deposition rates occur at the Holocene epoch but not for the Pre-Holocene lowest water levels� The strongest dissolution – during the Pre-Holocene net dissolution rates rates at other locations (Postojna-Planina cave prevailed or at least equilibrium between annual system, Lekinka cave, Križna Jama-Križna Jama dissolution and annual sinter deposition was 2 cave system) primary depend on the influence reached� of other factors (origin of high water, seasonal The strongest dissolution or sinter deposition changes of soil CO2 concentration, seasonal rates are characteristic only for places where changes in ventilation…)� Similarly, the highest the strongest deviation from SiC = 0 exist; recorded sinter deposition rates were not related this is due to high H+ concentration and low to the lowest discharge but on winter ventilation Ca2+ concentration (e�g� Lekinka cave) or due to of the cave (Križna Jama)� Nevertheless, for the the depletion of H+ cations (rise of pH) as a result highest sinter deposition rates discharge should of the outgassing of CO2 from the water (e�g� not be very high� it would be interesting to Križna Jama)� The strongest annual dissolution observe seasonal variation of dissolution and rates were detected in Lekinka (on average sinter deposition in other stream caves since -61�1 µm/a at measurement location L-1) and the a similar course of processes can be expected highest sinter deposition rates in Križna Jama (on in other caves recharged by intensive diffuse average 87�4 µm/a at Brzice (rapids) downstream infiltration of percolation water and can therefore from the first lake)� Rates during the 15-day be a universal phenomenon of temperate zones� measurement period can be, due to very high usual y, spatial variability of dissolution or weekly and even daily variation, much higher, sinter deposition rates along cave streams are low for example -9�0 µm/15 days (-219 µm/a for (Škocjanske Jame, Postojna-Planina cave system), comparison) for dissolution rates and more than but if we are close to changes of CO2 and Ca2+ in 130 General Conclusions, Discussion and Potential for Further Research the water and if the exchange of matter between and can be responsible for the majority of carbonates-water-air is considerable, very high denudation� in our case studies, a higher influence spatial variability can be observed� Tributaries of corrasion can be expected in Škocjanske Jame of allogenical y and autogenical y recharged and in Lekinka cave since they are both fed by water in the Postojna-Planina cave system do allogenic streams� Corrasion due to bed load not significantly influence dissolution or sinter transport can be seen in Škocjanske Jame as deposition rates, while in Križna Jama the highest polished surfaces in the bed of a channel and sinter deposition rates are significantly reduced corrasion rates there are much higher than rates downstream of the confluence with autogenical y of dissolution� At such places, limestone tablets recharged tributaries that have higher partial were severely damaged by bed load material� pressure of CO2� The influence of mixing corrosion Nevertheless, even some centimetres away, where can be detected at some measurement locations high concentration of suspended load can be (e�g� at Kalvarija (calvary) in Križna Jama) but expected, net sinter deposition rates (0�4 µm/a) it seems that its importance is exaggerated in can be stronger than rates of corrasion, which the literature since we observed other factors of can be proven by the presence of preserved (and greater importance (e�g� outgassing of CO2 from most probably thickening) flowstone coating� the water at the confluence of the Pivka and Rak Measurements undertaken several metres higher Rivers in the Postojna-Planina cave system)� up in the water channel show that corrasion rates to a 10-times high difference in sinter deposition from suspended load together with dissolution rates (Križna Jama-Križna Jama 2 cave system) is weaker than -0�2 µm/a� in Lekinka cave, or about 10 % difference in dissolution rates the influence of corrasion is less expressed in (Lekinka cave) can also be a result of hydraulic morphology� Results of measurements at least differences between measurement locations, in show that corrasion as a result of suspended load our cases between rapids and pools/lakes� is negligible compared with dissolution� Although dissolution and corrasion are quite in many cases, rates of dissolution or sinter/ different processes, they can be ‘cooperative’ tufa deposition are not equal in cave streams and and support each other (dissolution can remove in surface streams� in the latter, dissolution rates cement and corrasion tears off the weakly attached can be much higher due to high biocorrosion crystals)� Therefore, strict differentiation between (up to -150 µm/a)� Therefore, rates at il uminated the two is not possible� Nevertheless, in some springs or ponors cannot be applied to caves cases corrasion strongly prevails over dissolution located upstream or downstream� 4.3 Relation between present-day processes, factors and features We suppose and did indirectly confirm that taken during times of significant discharge with factors can change significantly over several a return period of ~50 years� Such discrepancies hundreds of thousands (even a million or more) were greatest where the direction of present-of years� This influences the direction and rate of day processes is of controversial morphology chemical processes and results in a changeable (i�e� dissolutional morphology with prevailing morphology of caves� Although we performed sinter deposition) and rates are weak� in such short-term measurements with a chosen cases, inherited features are obvious in the bed methodology, sometimes serious discrepancies of a channel (Postojna-Planina cave system) were detected between actual and potential or slightly higher up (Križna Jama and to some morphology even though the measurements were extent Križna Jama 2)� 131 General Conclusions, Discussion and Potential for Further Research There are stream caves where the current regime should result in lower hardness of water prevailing sinter deposition rates are in (Nanoščica River) and higher dissolution rates� contradiction with cave formation or with at in Lekinka, the biggest wall notch 75 cm from the least actual cross-sectional morphology� From bed of the channel and the current dissolution such cases, where thickness of actual flowstone rates (-61�1 µm/a) suggest that the wall notch coating fits with potential thickness of flowstone was formed during the Younger dryas stadial coating if present-day sinter deposition rates when the climate was the coldest in the Late are extended through the Holocene epoch, it is Pleistocene and the wall notch development can clear that an important change of direction and/ possibly be due to the protection of the bed of or rates of chemical processes in cave streams the channel during more intensive transport and were caused by climate change between the last accumulation of sediment� ice Age during the Pleistocene and Holocene4� Where the rates of chemical process are This can be interpreted through the influence of stronger, a high correlation was recognized temperature, length of vegetation season and soil between morphology and processes� The actual microbial activity, partial pressure of CO2 in the morphology of Škocjanske Jame that shows percolation water and consequential potential flowstone coating at the bottom of a channel, for the outgassing of CO2 from autogenical y scallops 1�5 m higher and absence of scallops recharged water� The decrease of CO2 partial more than ~2 m above the bed of the channel, pressure in the water was recognized as an is concordant with average annual chemical important factor for the downstream increase processes in the Reka River and certain other of SiC in Križna Jama and most probably also factors (flooding, freezing in winter time)� in occurs in the Pivka River between its spring and Križna Jama in the first lake and downstream ponor in the Postojna-Planina cave system� More at Brzice (rapids), morphology in the bed of the intensive direct runoff from the surface due to channel also comports with the present direction partly frozen ground or different precipitation and rates of processes� 4 This phenomenon was already observed in the growth of stalagmites (Mihevc 2001) and tufa dams but it was rarely attributed to speleogenesis in stream caves in an epiphreatic (or shal ow phreatic) zone. 132 P 5 OVZETEK 5.1 Uvod Sedanje poznavanje kraških oblik, dejavnikov tega precej slabše poznana, tudi v svetovnem in procesov temelji na več kot stoletje dolgem merilu (Gunn 1986)� Velik primanjkljaj je intenzivnem proučevanju kraških pojavov� Prva predvsem na nivoju poznavanja dinamike temeljna spoznanja in konceptualne ideje o recentnih procesov, kar velja za celotno področje kraških pojavih imajo korenine že v 19� stoletju, slovenske geomorfologije (Natek 1993; 48 po ko so bile poznane osnove raztapljanja karbona- Natek 1983; 87)� Načrti o meritvah geomorfne tov, vloga CO2, osnovni mehanizmi pretakanja aktivnosti podzemnih voda sicer segajo že v 60� vode in vertikalna conacija kraških masivov� V leta 20� stoletja, vendar niso bili načrti nikoli 20� stoletju se je to znanje večinoma le še izpopol- realizirani� Precej bolje so raziskani dejavniki, njevalo, močno poglobilo, razvoj jamarske tehni- ki vplivajo na kraške procese, vendar ne nujno z ke pa je omogočil tudi boljši vpogled v notran- geomorfološkega vidika (npr� fizikalno-kemijske jost kraških masivov� Rezultati meritev podani analize voda, litološke litološke značilnosti v tej monografiji niso nič več kot le dodaten kamnin)� Pri naštetem se primanjkljaj kaže v delček v mozaiku znanja o krasu, ki ga lahko z geomorfološkem vrednotenju hidroloških in izboljšanimi metodami tudi vse bolj točno kvan- litoloških podatkov� Precej bolj pestro in široko tificiramo, obenem relativiziramo, predvsem pa je znanje o speleomorfologiji, ki je najbolj očiten čedalje bolje objektivno spoznavamo� in najlažje prepoznaven rezultat učinkovanja Naslov monografije omejuje njeno kraških procesov pod vplivom dejavnikov� dimenzijsko razsežnost, in sicer v času (današnji izstopa predvsem proučevanje morfologije pojavi), vodilnemu predmetu (procesi) ter večjih aktivnih in fosilnih jamskih rovov, ki prostoru (vodne jame)� Recentna dinamika nam pogosto ne poda le informacij o razvoju je bila v slovenski geomorfologiji, pa tudi v jame, ampak tudi o razvoju okolice, ki je močno svetovni speleologiji, vedno v senci drugih raziskav, ki so bile osredotočene na pretekli vezana na jamo� Tudi v tej monografiji smo običajno zelo dolg razvoj jam (speleogenezo)� To se osredotočili na proučevanje pomembnejših je povezano z željo po časovno čim celovitejšem aktivnih vodnih jam, pri katerih smo si zastavili proučevanju razvoja jam, ki v krasu običajno naslednje cilje: poteka več 10�000, 100�000 ali celo nekaj • testiranje metode merjenja procesov z milijonov let� Recentna morfodinamika je zaradi apnenčastimi ploščicami, uvesti izboljšave 133 Povzetek na področju ustreznejše pritrditve in merske podzemna voda (Slika 1�1a na strani 12)� Pri natančnosti ter metodo primerjati z drugimi tem se je pogosto zavračalo dejstvo, da recentne razpoložljivimi metodami za ugotavljanje oblike morda ne nastajajo več z recentnimi recentnega raztapljanja, procesi, saj so se dejavniki v času spremenili (npr� • ugotoviti smer in intenziteto recentnih speleogenetskih procesov v pomembnejših sprememba klime, hidroloških razmer v porečju, vodnih jamah slovenskega krasa ter opredeliti tektonski premiki) in so zato lahko dediščina vodilne dejavnike, ki na procese vplivajo, in procesov v preteklosti� Pogoj za dolgoročno oblike, ki pri tem nastajajo, ohranjanje oblik je majhna intenziteta procesov, • izboljšati vpogled v povezavo med ki je bila že prepoznana v nekaterih študijah speleogenetskimi procesi, dejavniki in (Spate et al� 1985, Gams 1996)� Zaradi tega smo za oblikami, proučevanje recentne in pretekle morfodinamike • določiti potencialne speleogenetske oblike, uporabili drug pristop (Slika 1�1b), pri katerem ki z recentnimi procesi šele nastajajo, in jih smo ločili recentne procese z dejavniki od primejati z aktualnimi oblikami v kraškem aktualne morfologije� Ločenost analize nam podzemlju, ki so lahko podedovane� omogoča navzkrižno primerjavo med aktualno Običajno se je na recentne procese sklepalo in potencialno morfologijo ter določitev preteklih iz podzemnih oblik, ki jih občasno dosega dejavnikov, v kolikor je odstopanje očitno� 5.2 Raziskovalne metode Za meritev recentnih procesov smo uporabili metrične enote zlasti težko določljiva reakcijska mikrometrske meritve, apnenčaste ploščice, v površina� Rezultati prostorskih meritev vzdolž omejeni obliki pa tudi hidrokemično metodo� toka nam torej veliko bolje podajajo smer procesa Mikrometrske meritve so najbolj uporabljena (raztapljanje ali odlaganje) kot pa dejansko metodologija za ugotavljanje mehanskih intenziteto le-tega� (korazijskih) in kemičnih procesov na krasu V želji po čim bolj natančnih meritvah smo (npr� High & Hanna 1970 po White 2000, največ meritev opravili z metodo apnenčastih Spate et al� 1985, Mihevc 1993, Mihevc 1997, ploščic, ki smo jo pred (poglavje 2�2�2) in Mihevc 2001), saj je metoda enostavna, meri se tekom meritev na posameznih izbranih dejansko odmikanje (ali približevanje) jamske primerih (poglavje 3) preizkušali ter jo tudi stene, omogoča več meritev na istem mestu ter primerjali z mikrometrskimi meritvami� S izračun standardnih odklonov na posameznih strani raziskovalcev procesov na krasu so bile vzorčevalnih ploskvah� Slabosti metode so apnenčaste ploščice običajno uporabljene za relativno visoke napake meritev, katerih vpliv meritve intenzitete raztapljanja v prsti (Trudgill se veča s šibkostjo procesov (Spate et al� 1985)� 1975 po Gavrilović & Manojlović 1989, Jennings Hidrokemične meritve so se večinoma izvajale 1977 po Gavrilović & Manojlović 1989, Trudgill na izvirih z meritvami prevodnosti, s katero se 1977, day 1984 po Gavrilović & Manojlović 1989, določa celokupna trdota, in meritvami pretokov� Gavrilović 1986 po Gavrilović & Manojlović Čeprav omogoča metoda tudi ugotavljanje 1989, Sbai 1993, Trudgill et al� 1994, urushibara-raztapljanja oz� odlaganja sige med dvema Yoshino 1999 po Ford & Williams 2007, Plan točkama vzdolž podzemnega toka brez vmesnih 2005), le redko tudi v jamah (Chevalier 1953 po pritokov, je slabost pri preračunavanju v Gams 1985, Gams 1959, Rebek 1964, delannoy 134 Povzetek 1982 po Gams 1985, Gams 1996)� Teoretično stene� Zaradi drobnih deloma zdrobljenih je lahko ta metoda veliko natančnejša od kristalov na površini apnenčaste ploščice, lahko mikrometrske, saj izračunavamo tanjšanje na začetku meritev pričakujemo do okoli 2 µm ploščic iz dosti lažje določljive razlike v teži, na 15 dni višjo intenziteto raztapljanja (Slika 2�6 vendar tudi njo spremlja več potencialnih napak� na strani 23)� Razlika izgine, ko je odstranjena Prva je povezana z vplivom spreminjajoče se okoli 25 µm debela plast apnenčaste ploščice� relativne vlažnosti pri tehtanju, ki so se jo v Še večja razlika se pojavlja pri odlaganju sige preteklosti ognili s sušenjem apnenčastih ploščic (Slika 2�7 na strani 24)� del variabilnosti izhaja v pečici pri temperaturah nad 100 °C in v silica tudi zaradi heterogenosti med apnenčastimi gelu (Gams 1985), kar pa pri večkratni uporabi ploščicami, in sicer v povprečju ±0,5 µm taistih apnenčastih ploščic lahko pripelje do na 15 dni (največ -1,3 ter 0,7 µm na 15 dni), intenzivne migracije vode iz notranjosti na vendar so razlike v daljšem časovnem obdobju površino apnenčastih ploščic in neželenega povprečene, zato je topnost v daljšem obdobju otrdevanja površine (t�i� case hardening)� praktično enaka (Slika 2�6 na strani 23)� Največja Klasično sušenje več deset ploščic v 15-dnevnem odstopanja lahko izhajajo iz različne litološke zamiku preko več let bi bil tudi znaten tehničen sestave ploščic� V kolikor merimo z apnenčastimi zalogaj� Zaradi tega smo uvedli korekcijski faktor, ploščicami, odstopanja niso velika (do 20 %; ki izniči spremembo relativne vlage v kemijskem Slika 2�8 na strani 26)� Če pa merimo v jamskih laboratoriju inštituta za raziskovanje krasa ZRC rovih izoblikovanih v dolomitu, je lahko hitrost SAZu, kjer so bile meritve opravljene (Slika 2�3 raztapljanja zlasti ob precejšnji nenasičenosti na strani 20)� S tem korekcijskim faktorjem in vode (Gerstenhauer & Pfeiffer 66 po Sweeting ob odsotnosti drugih znanih vplivov smo vpliv 1972; 28-29, Chou et al� 1989 po dreybrodt 2004; napake pri 20-25 g težkih ploščicah zmanjšali na 297-298) do 90 % nižja� Precejšen del napake povprečno ±0,2 µm, največ pa ±0,4 µm napake� lahko izhaja tudi iz poškodb pri transportu, Le-to se da še nadalje zmanjšati s terensko vendar se ji lahko v celoti ognemo s prenašanjem uporabo korekcijskih ploščic, ki jih vodni tok ni ploščic v posebej za ta namen izdelanem nosilcu dosegel, so pa bile postavljene, pobrane in sušene (Slika 2�5 na strani 22)� Primerjava med metodo skupaj s ploščicami, ki jih je vodni tok dosegel� S apnenčastih ploščic in mikrometrom pokaže, tem pridobimo na točnosti, večjo preciznost pa da sta raztapljanje in odlaganje sige izmerjeni z dobimo z uporabo večjega števila apnenčastih mikrometrom običajno intenzivnejši v primerjavi ploščic na istem mestu (Slika 2�1�3�6; Slika z meritvami z apnenčastimi ploščicami (Slika 2�9 2�1�3�7)� S tem se povprečna napaka zmanjša na in 2�10 na strani 27)� Ni nujno, da napaka izhaja ±0,05 µm, maksimalna pa na ±0,2 µm� Znatno le zaradi uporabe apnenčastih ploščic, saj lahko napako pri merjenju lahko povzroči oksidacija tudi uporaba mikrometra pripelje do nekaj železa, ki ga uporabljamo za pritrditev� intenziteta µm velikih napak (npr� velike temperaturne zavajajočega raztapljanja, ki se pri tem pojavlja, je razlike med posamičnimi meritvami, abrazija močno odvisna od lokacije in znaša od 0,0 do -2,4 z mikrometrsko konico)� Čeprav obe meritvi µm v 30 dneh merjenja (slika 2�4 na strani 21)� izkazujeta enako magnitudo procesov, so Zavajajočemu raztapljanju s strani železovega lahko odstopanja precejšnja in terjajo nadaljnje oksida se lahko izognemo s pritrditvijo ploščic proučevanje� na nerjaveč ali plastičen vijak� Med njimi Metodologija merjenja procesov z bistvenih razlik ni opaziti� del napake pri apnenčastimi ploščicami je bila preizkušena meritvah z apnenčastimi ploščicami je povezan na 85 lokacijah večinoma po slovenskem krasu tudi s sveže odrezano nepreperelo površino, ki v 8-mesečnem merilnem obdobju� Rezultate se obnaša drugače od deloma preperele jamske meritev temeljiteje analizira Prelovšek (2009) 135 Povzetek v svoji doktorski disertaciji� Na tem mestu naj elektroprevodnost (SEP) kot vsota vseh razto-opozorimo le na ugotovljeno nizko intenziteto pljenih snovi, pH kot koncentracija H+ ionov in kemičnih procesov v vodnih jamah (večina med temperatura so bili izmerjeni z merilcem WTW -1 in -10 µm/a, povprečje -7�4 µm/a, mediana -1,5 Multiline P4 in ustreznimi sondami na terenu� µm/a), večkrat prevladujočo smerjo odlaganja indeks nasičenosti glede na kalcij (SiC) je bil sige namesto raztapljanja ter znatno večjega ob pridobljenih koncentracijah Ca2+, Mg2+, al-raztapljanja na izvirih v primerjavi z jamami v kalnosti, T, SEP in pH izračunan s programom zaledju zaradi vpliva biokorozije� Pri meritvah WATEQ4F (Ball & Nordstrom 1991)� Pretok je potrebno predvsem na alogenih vodotokih vode smo merili z injektiranjem vodne raztopine upoštevati tudi pojav korazije� Regionalne in NaCl v vodotok ter dolvodnim merjenjem SEP lokalne razlike so lahko majhne ali izredno v znanem časovnem intervalu (Käss 1998) ter velike; med največjimi so med Postojnsko jamo določeni pretočni krivulji (Križna jama in Le-in Lekinko, ki sta oddaljeni le kilometer, v samih kinka)� Vodostaj smo ugotavljali bodisi vizual-rovih pa na intenziteto procesov vpliva tudi no bodisi z digitalnim registratorjem vodnega višina merjenjav jamskem rovu� nivoja Schlumberger Td-diver� Med marcem in Fizikalno-kemične lastnosti vode smo ugo- oktobrom 2007 smo v Križni jami za meritve vo- tavljali z meritvami v laboratoriju in na ter- dostaja, temperature in SEP uporabljali Gealog S� enu� Koncentracija Ca2+ je bila ugotovljena s Karakteristike zraka smo ugotavljali kompleksometrično titracijo z 0,01 M EdTA, predvsem z vidika gibanja (intenziteta, smer) koncentracija Mg2+ pa z odštevkom koncen- ter koncentracije CO2� Prostorske meritve tracije Ca2+ od celokupne trdote vode� Alkalnost ter meritve v 20 do 12 dni dolgem časovnem je bila ugotovljena s titracijo z 0,02 M HCl pri razponu smo izvajali s prenosnim merilcem končnem pH = 4,5� Obe koncentraciji sta nam CO2 Vaisala GM70 z pripadajočo sondo GMP222 omogočili izračun razmerja Ca/Mg� Specifična z maksimalno koncentracijo 3�000 ppm� 5.3 Izbrani primeri s slovenskega krasa Jamski sistem Križna jama-Križna jama 2 dobro prevetrena, zlasti ko zunanja temperatura Sistem obeh Križnih jam leži v sredini trikotnika znatno odstopa od jamske (8 °C)� Pozimi je prepih med Cerkniškim poljem, Loškim poljem in usmerjen skozi glavni vhod v jamo, poleti pa Bloško planoto� Preko 9�688 m dolg in pretežno priteka jamski zrak skozi glavni vhod na površje� vodoraven jamski sistem je razvit v tektonsko Križna jama 2 je prevetrena v znatno manjši meri, slabo pretrtih spodnje jurskih apnencih� Skrajni predvsem zaradi majhnega in verjetno edinega gorvodni deli Blat ležijo že v spodnje jurskem večjega vhoda� Glede na meritve Mihevca (1997) zrnatem dolomitu� Jamski sistem sestavlja v je prevladujoč geomorfni proces v Križni jami grobem en glavni vodni rov, ki se gorvodno odlaganje sige s hitrostjo 128 µm na leto� od Kalvarije (Križna jama) razcepi v rov Blata S podrobnejšimi meritvami smo pričeli in južneje ležeči Pisani rov� Vsi rovi prevajajo februarja 2006 in končali aprila 2009� izvajali preniklo vodo, le ob višjih vodostajih se ji pridruži smo jih na 14 merilnih mestih v Križni jami in tudi tok z Bloške planote (Kogovšek et al� 2008)� na 6 merilnih mestih v Križni jami 2 (Slika 3�1�6 Zaradi tega ima voda visoko celokupno trdoto, na strani 40)� interval meritev je bil odvisen od relativno stabilno letno temperaturo in ima visok dostopnosti merilnih mest in je segal od 15 dni parcialni tlak CO2� Pretok znaša od 0 do nekaj m3/s do več kot pol leta� Meritve procesov smo izvajali (običajno okoli 0,1 m3/s)� Križna jama je izredno z apnenčastimi ploščicami, mikrometrom ter 136 Povzetek hidrokemično metodo, za ugotavljanje fizikalno- v odlaganju sige med brzicami in jezerom kemičnih lastnosti vode smo uporabljali merilec odsotne, s tem pa tako dolga jezera v Križni jami prevodnosti, pH, temperature in vodostaja� Za sploh ne bi mogla nastati� domnevamo, da gre meritve v zraku smo uporabljali prenosni merilec pri povezavi odlaganja sige s prepihom tudi za koncentracije CO2� povratno zanko – z zviševanjem sigovih pregrad 15-dnevna merjenja kraških procesov 10 m se zračni prehod med jezersko gladino in stropom dolvodno od 1� jezera (merilno mesto KJ-1) v niža, s tem se manjša stopnja prezračevanja jame večinoma stalno zaliti coni so pokazala, da je v zimskem času, ki povratno vpliva na manjše prevladujoč proces odlaganje sige� intenziteta le- odlaganje sige na pregradah in v jezerih� Hitrost te prvenstveno ni odvisna od vodostaja, temveč odlaganja sige se tako sčasoma zmanjšuje� od intenzitete in dolgotrajnosti prepiha v jamo Z meritvami prostorskih zakonitosti pozimi (Slika 3�1�11 na strani 45)� Največje odlaganja sige med Brzicami pod 1� jezerom odlaganje sige smo zabeležili ob dolgotrajnem in Kalvarijo smo ugotovili, da se intenziteta intenzivnem prepihu v jamo, ki običajno nastane, odlaganja sige gorvodno znižuje (Slika 3�1�16 ko ostane zunanja temperatura preko dneva pod na strani 51)� To je povezano z naraščajočim SiC -2 °C� V taki meteorološki situaciji so pogoji za pod sotočjem potoka iz Pisanega rova s potokom izhajanje CO2 iz vode dovolj ustrezni za znatno iz rova Blata� Pri mešanju voda sicer ne prihaja zvišanje SiC ter s tem za znatno odlaganje sige� do intenzivne korozije mešanice, vseeno pa se Tako se v nekaj dneh odloži praktično vsa letna odlaganje sige pod sotočjem močno zmanjša� V količina sige� Količina letno odložene sige je kolikor je zimski prepih premalo intenziven, na prvenstveno odvisna od intenzitete in trajanja gorvodnih sigovih pregradah do odlaganja sige zimskega prepiha v jamo in lahko znaša do 17 sploh ne prihaja� Morfološki rezultat tega pojava µm/15 dni� V preostalem delu leta je intenziteta je viden v tanjšanju sigove prevleke na stenah kraških procesov nizka (manj kot ±0,5 µm/15 jezer od 1� jezera do Kalvarije in pa predvsem dni)� Korazije kljub evidentiranemu prenosu v upočasnjeni rasti gorvodnih sigovih pregrad suspendiranega materiala tudi ob visokih v primerjavi z dolvodnimi� Le-to pripelje do vodostajih nismo zasledili� poplavljanja gorvodno ležečih pregrad s strani Z meritvami na merilnem mestu KJ-2 dolvodnih ter daljšanje jezer od 1� jezera proti smo poskušali dobiti vpogled v intenziteto Kalvariji (Slika 3�1�18 na strani 54)� Meritve na raztapljanja, saj smo 21 apnenčastih ploščic Kalvariji so pokazale tudi na sezonsko pogojenost razvrstili navpično v območje najpogostejšega kemičnih procesov (Slika 3�1�20 na strani 57); nihanja vodne gladine v 1� jezeru� Zgornje v poletnih in jesenskih mesecih prihaja do ploščice, ki so bile izpostavljene zgolj visoki vodi, skromnega raztapljanja (okoli -0�3 µm/30 dni), v v skoraj 3 letih merjenja niso povsem zanesljivo zimskih in spomladanskih pa do odlaganja sige pokazale na raztapljanje� Spodnje ploščice, ki so (okoli 0�6 µm/30 dni)� bile izpostavljene tako odlaganju sige kakor tudi Sezonski potek kraških procesov v Pisanem potencialnemu raztapljanju, so pokazale daleč rovu v grobem ustreza razmeram v rovu med prevladujoč proces odlaganja sige, kljub temu 1� jezerom in Kalvarijo� Tudi tu prihaja zaradi pa precej manj kot na brzicah pod 1� jezerom močnega prepiha do odlaganja sige izključno v (merilno mesto KJ-1)� intenziteta odlaganja je zimskem in zgodnjem spomladanskem času� bila na obeh merilnih mestih enaka v času nizkih Odlaganje sige se gorvodno po Pisanem rovu odlaganj sige, glavne razlike pa so nastajale v času zmanjšuje (Slika 3�1�21 na strani 59)� visokih zimskih prirastkov sige, ki so pogojeni V rovu Blata so geomorfne razmere precej s prepihom v jamo� V kolikor intenzivnega in bolj zapletene, saj se srečujemo z več dotoki, ki dolgotrajnega prepiha ne bi bilo, bi bile razlike popolnoma ustavijo odlaganje sige (primer je 137 Povzetek na Sliki 3�1�23 na strani 63), vendar se le-to po ali pa mikroorganizmi� Podoben razkorak med nekaj sto metrih toka znova okrepi� Kljub temu procesi in oblikami sledimo tudi pri fasetah, ki je odlaganje sige v rovu Blata precej manjše v so dobro ohranjene povsod po jamskem sistemu, primerjavi z odlaganjem v Pisanem rovu ter vendar je raztapljanje izjemno skromno� Tudi med 1� jezerom in Kalvarijo, vendar precej ker velikost faset marsikje ne ustreza današnjih bolj sezonsko in zvezno� Glavnina odlaganja hidrodinamičnim razmeram v jamskem sistemu sige je sezonsko pogojena in se tudi tu zgodi v ocenjujemo, da so fasete fosilne/podedovane spomladanskih mesecih, nato sledimo upad in se danes ne oblikujejo več� dosti boljše odlaganja sige ter celo prehod v raztapljanje, v razmere za njihovo rast so bile v hladnejših zimskem času pa skromno raztapljanje zopet obdobjih pleistocena, ko je sta bila trdota vode preide v skromno odlaganje sige� Ta prehod je in koncentracija CO2 nižja zlasti ob visokem opazen skozi vso Križno jamo in Križno jamo 2, vodostaju� To je ugodneje vplivalo na razvoj faset vendar je marsikje manj razpoznaven zaradi kot razmere v današjem času� intenzivnega odlaganja sige ob intenzivnih prepihih� Edina povezava raztapljanja z visoko Lekinka vodo je bila ugotovljena na pritoku v rov Blata (KJ- Lekinka je tipična ponorna jama na 12), kjer so visoki zimski pretoki, najverjetneje severovzhodnem robu Pivške kotline 1 km tudi s strani podzemeljske Bloščice in Farovščice, severozahodno od ponora Pivke v Postojnsko povzročili raztapljanje intenzivnejše od napake jamo� iz približno 1 km2 velikega porečja merjenja (-0,4 µm)� na pleistocenski terasi Nanoščice in Pivke V Križni jami 2 sledimo podoben potek (Gospodarič & Habič 1966) odvaja vodo Črnega odlaganja sige in raztapljanja kot v rovu Blata potoka (Slika 3�2�1 na strani 76)� Zaradi nizkih (Slika 3�1�24 na strani 65)� Sezonski impulz se reliefnih amplitud v porečju Črni potok prenaša torej prenaša preko celotnega jamskega sistema� malo talnega materiala, je pa zaradi močvirnih Tudi količina letno odložene sige je v Križni razmer v porečju toliko bolj izrazita nizka jami 2 (0,6 µm na leto) enaka rovu Blata zaradi vsebnost karbonatov in vsebnost organskih visokih koncentracij CO2 preko zime (Slika 3�1�25 snovi v vodi� V Lekinki lahko v dolžini 790 m na strani 66), kar se pozna tudi pri konstantnem spremljamo podzemni tok Črnega potoka, pH preko celotne jame (Slika 3�1�27 na strani 69)� preden se ta pridruži podzemeljski Pivki v dolvodno se količina odložene sige sicer poveča Otoški jami� Le-ta ob visokem vodostaju vpliva (na 2 µm na leto; Slika 3�1�26 na strani 68), vendar na retrogradno poplavljanje tudi v Lekinki, ob je povečevanje zaradi višjega CO2 dosti manjše v izredno visokih vodostajih Pivke in Nanoščice primerjavi s tistim, zabeleženim v Pisanem rovu pa slednja tudi vdre v porečje Črnega potoka ali med 1� jezerom in Kalvarijo� in za vsaj 8 m poplavi Lekinko (Slika 3�2�2 na Prevladujoč proces odlaganja sige se ujema z strani 78)� Take poplave zgolj s strani Črnega morfološko izraženimi sigovimi pregradami in potoka niso možne, saj imajo rovi Lekinke sigovimi prevlekami v jezerih� Ob sedanji hitrosti dovoljšen prečni presek za prevajanje nekaj m3/s rasti se začetek intenzivnega odlaganja sige umešča vode� Ob običajnem vodostaju teče v Lekinko na prehod iz pleistocena v holocen (12�000 B�P�)� 0�05 m3/s� Zaradi drugega vhoda, najverjetneje Odstopanja med ugotovljenim, a morfološko skozi Otoško jamo, je Lekinka dobro prevetrena� neizraženim odlaganjem sige sledimo v Križni Meritve intenzitet kraških procesov v več jami 2, kjer smo zasledili prevladujoč skromen vodnih jamah v 8-mesečnem obdobju so proces odlaganja sige in odsotnost sigovih pokazale na razmeroma visoko intenziteto prevlek� Zaradi nizke intenzitete odlaganja sige raztapljanja, ki je lahko intenzivnejša od -100 µm je možno, da plasti sproti odstranjuje korazija na leto� Nadaljnje meritve na merilnem mesti 138 Povzetek L-1 med septembrom 2006 in aprilom 2009 so pa dno v obliki črke u� Pri tem je nujno, da ob visoke vrednosti potrdile, vendar kljub temu srednjem vodostaju vodna gladina s stenami pod niso presegle -80 µm/a (Slika 3�2�6 na strani 82)� vodo tvori ostri kot� Le v tem primeru se lahko Meritve na L-1, ki so bile opravljene z 15-dnevnim meander z enako mero poglablja kakor tudi širi intervalom merjenja, so pokazale na razmeroma v obe smeri� Tako obliko meandra v Lekinki močno odvisnost intenzitete raztapljanja dejansko opazujemo (Slika 3�2�12 na strani 89)� od količine padavin v 15 dnevnem obdobju Meritve raztapljanja vzdolž podzemnega (R2 = 0,55)� Korelacija intenzitete raztapljanja z toka med ponorom in odtočnim sifonom (Slika maksimalno višino vode v 15-dnevnem obdobju 4�2�5) so pokazale dva dolžinska območja je nižja (R2 = 0,31), predvsem zaradi nekaj visokih raztapljanja� V prvem dolgem 250 m sledimo vodostajev, ki se zaradi kratkotrajnosti poplav hiter eksponenten upad raztapljanja (za 54 %), niso izrazili v najvišjih vrednostih raztapljanja nato pa se upadanje raztapljanja praktično v 15-dnevnem obdobju� V opazovanem obdobju ustavi� Tako smo 790 m od ponora zabeležili še nismo zasledili nobenega izrazitega sezonskega vedno 50 % raztapljanja značilnega za ponor� vpliva (Slika 3�2�8 na strani 84), ki bi bil povezan Pričakovali bi, da je upad raztapljanja rezultat s sezonskim nihanjem temperature vode, čedalje bolj nasičene vode, vendar se glavna koncentracije organskih snovi (kislin) v vodi odvisnost kaže od parcialnega tlaka CO2 v ali koncentracijo CO2 v vodi (kot posledica vodi (Covington et al�, v tisku)� Na intenziteto temperature vode ali biološke produkcije v tleh)� raztapljanja vplivajo še drugi dejavniki, npr� Na merilnem mestu L-1 smo z 11 apnenčastimi dotoki avtigene vode, razpad organskih snovi in ploščicami opazovali višinsko spremenljivost sedimentacija ilovice, zato upad raztapljanja od raztapljanja (Slika 3�2�10 na strani 87)� V ponora do Končnega sifona ni zvezen� Zabeležili skladu s pričakovanji je bila največja intenziteta smo vpliv hitrosti toka, ki vpliva na raztapljanje zabeležena v spodnjem delu jamskega rova, sledil preko debeline difuzijske plasti – ko se prične pa je izjemno hiter upad raztapljanja navzgor� retrogradno poplavljanje s strani podzemeljske To pomeni, da je voda zmožna raztapljanja Pivke, intenziteta raztapljanja v Lekinki ne tudi ob nizkem vodostaju, najbolj efektivno pa narašča več� Na intenziteto raztapljanja na koncu raztaplja ob srednjem vodostaju, ki se pojavlja jame vpliva tudi hitrost vodnega toka – ob višjem najpogosteje� Največjo agresivnost doseže voda vodostaju je hitrost pretoka hitrejša, raztapljanje ob najvišjem vodostaju, vendar so ti tako redki pa dolvodno tudi počasneje usiha� in časovno zelo omejeni, tako da je raztapljanje v Ponor Lekinke leži približno 1 m nižje višjih delih jamskega rova precej manjše, jamski od ponora Pivke v Postojnsko jamo� Hitro rov pa se tam najmanj spreminja� Velik upad poglabljanje Lekinke in praktično nično raztapljanja z višino, dokaj nizka variabilnost poglabljanje Pivke bo sčasoma v porečju Črnega vodostaja in zaščitenost skalnega dna s talnim potoka ustvarilo močan gradient, ki ga bodo materialom so izjemno ugodni pogoji za razvoj vse pogosteje izkoristile vode Nanoščice� Le-stenskih zajed� V tem primeru se rov širi bočno te se že sedaj ob zelo visokih vodah prelivajo levo in desno, poglabljanje pa le navzdol, pa še preko razvodnice� Meritve raztapljanja ob tod lahko stalni dotok talnega materiala ščiti takih situacijah kažejo, da Nanoščica zavre dno jamskega rova� V kolikor ga ne, sledimo intenzivno raztapljanje v Lekinki� V kolikor bo bodisi epifreatično širjenje in poglabljanje prišlo do stalne pretočitve Nanoščice v Lekinko v osnovi freatičnih rovov bodisi vrezovanje (ta vodna smer je pravzaprav bližnica v Otoško vadoznega meandra� Le-ta lahko ohranja širino jamo), bo Lekinka doživela znatne spremembe v le v ravnotežni spodnji obliki, ki jo v zgornjem preoblikovanju s strani raztapljanja� Predvsem delu sestavljata vzporedni steni, v spodnjem delu lahko pričakujemo znaten upad raztapljanja, 139 Povzetek prenehanje nastajanja meandra ter bolj freatičen potrjuje tudi dokaj majhna največja zabeležena način širjenja jamskih rovov zaradi večjega intenziteta raztapljanja, ki znaša okoli -0,4 µm/a nihanja vodostaja in majhne (oz� odsotne) približno 6 m nad dnom podzemne struge (Slika agresivnosti vode ob srednjih in nizkih 3�3�6)� Nižje je celokupno raztapljanje manjše vodostajih� Take spremembe so se verjetno v zaradi odlaganja sige ob srednjem-visokem preteklosti že dogajale v Postojnski jami, ko vodostaju, navzgor pa zaradi krajšega časa iz-vanjo morda ni vtekala Pivka� postavitve ob poplavi� Tudi pretok nad 200 m3/s decembra 2008 in kasneje v zadnjem merilnem Škocjanske jame obdobju se ni odrazil v bistveni intenziteti raz- Škocjanske jame spadajo na uNSECO seznam tapljanja� Prevlada raztapljanja nad odlaganjem svetovne dediščine predvsem zaradi zgodovine sige se zgodi, ko ima Reka pretok okoli 20 m3/s� odkrivanja podzemnega toka Reke ter Ker začne Reka ob nekoliko višjem pretoku že nadpovprečno bogato razvitega kontaktnega retrogradno poplavljati, je »okno« za skalne ob-krasa� Podzemni tok Reke poteka večinoma v like hitrega toka (npr� faset) s strani raztapljanja obliki podzemnega vintgarja, globokega do okoli izredno ozko� To se odraža tudi v morfologiji, saj 90 m� Navpične stene brez stenskih zajed kažejo, se fasete nad 2 m nad dnom struge ne pojavljajo da je vrezovanje potekalo enakomerno navzdol� več, odsotne pa so tudi v spodnjem 1,5 m visokem Proces vrezovanja je na nekaj točkah meril delu struge (Slika 3�3�7 na strani 109)� V tem delu Mihevc (2001) z mikrometrom� ugotovil je, da namreč prevladuje odlaganje sige v obliki sigovih je korazija razmeroma močan proces (od -160 do prevlek, ki jih v najnižjih delih struge lahko opa- -40 µm/a), medtem ko je raztapljanje precej zujemo v debelini okoli 6 mm� Glede na ta dejstva šibkejše (okoli -10 µm na leto, kar je v območju bi le-te lahko nastale v holocenu� napake merjenja z mikrometrom)� Korazija je dolžinske meritve intenzitete raztapljanja od povezana z okoli 350 km2 velikim porečjem, prestopa Reke iz silikatnih na karbonatne kam- katerega 60-75 % (Kranjc 1986; 112, Habič et nine pa vse do končnega sifona (Ledeni dihnik) al� 1989; 10, Kranjc & Mihevc 1988 po Mihevc kažejo, da je raztapljanje odstotno že ob presto-1991) leži na nepropustnih silikatnih kamninah� pu na karbonatne kamnine (Slika 3�3�8 na strani Kljub temu je celokupna trdota razmeroma 111)� To je skladno z ugotovitvami Gamsa (1962; visoka (10,3 °NT; Gams 1962; 278), kar prispeva 278) o precejšnji karbonatni trdoti Reke, s čemer k majhni intenziteti raztapljanja že na kontaktu se zmanjša tudi možnost raztapljanja� Razmere fliš-apnenec� Z natančnejšimi meritvami smo se vzdolž površinskega in podzemnega toka ne hoteli ugotoviti, kakšna je odvisnost raztapljanja spreminjajo bistveno – neto odlaganje sige znaša od pretoka Reke ter kolikšna je višinska ter med 0,3 do 0,9 µm/a� Visoko celokupno trdoto dolžinska spremenljivost raztapljanja� Reke lahko pripišemo številnim desnim kraškim Rezultati z merilnih mest S-1 in S-2 (Slika 3�3�1 pritokom Reke, ki odvajajo razpršeno infiltrirano na strani 103) kažejo, da ob srednjem in nizkem vodo z območja Snežnika in Zgornje Pivke, ter vodostaju prevlada odlaganje sige, medtem ko deloma karbonatnemu vezivu fliša� Levi pritoki meritve raztapljanja ob visokem vodostaju ovira s fliša kljub nizki trdoti visoke trdote v glavni korazija� Le-ta je bila na srečo odsotna (ali vsaj strugi ne uspejo znižati do te mere, da bi se voda močno zmanjšana) na spodnjih merilnih mestih v Škocjanskih jamah odrazila z raztapljanjem� pri Martelovem jezeru� Rezultati tam kažejo, da v spodnjem višinskem metru struge prevladuje Jamski sistem med Postojnsko kotlino in odlaganje sige (0,5 µm/a), ki se očitno odlaga ob Planinskim poljem srednjem in nizkem vodostaju, visoke vode pa ga Jamski sistem med Postojnsko kotlino in z raztapljanjem ne uspejo povsem odstraniti� To Planinskim poljem (jamski sistem Postojnske 140 Povzetek jame in Planinska jama) je hidrološko in dvignile nivo Pivke v Velikem domu za kar 8 m geomorfološko izjemno pomemben splet rovov, (Slika 3�4�6 na strani 121)� Raztapljanje smo saj v višinski razliki ~56 m povezuje Postojnsko zaznali ob znatno nižjem vodostaju, ko je bila kotlino s Planinskim poljem� Skupaj tvori kar Nanoščica višja in Pivka nizka� 27�226 m rovov, od katerih je več kot 10 km Na nizu merilnih mest med ponorom v vodnih� dostopnost rovov tako s postojnske Postojnsko jamo in izvirom v Planinsko jamo kakor tudi s planinske smeri nam nudi izjemen smo vseskozi beležili odlaganje (Slika 3�4�7 na vpogled v dinamiko procesov, dejavnikov in strani 123)� Najmanjše vrednosti smo zabeležili oblik vzdolž podzemnega vodnega toka, hkrati v Pivki jami, medtem ko se odlaganje dolvodno pa omogoča tudi vpogled v eno izmed največjih in gorvodno povečuje� Razlike med merilnimi podzemnih sotočij na svetu – sotočje Pivke in mesti so kljub temu majhne; še največje so v Raka v Planinski jami� vhodnem delu Postojnske jame, najverjetneje Meritve časovne in vertikalne spremenljivosti zaradi največjega dolvodnega upadanja odlaganja procesov smo izvajali v Velikem domu v organskih snovi iz vode� Pritoki bistveno ne vhodnem delu Postojnske jame (merilno mesto vplivajo na intenziteto raztapljanja ali odlaganja P-1; Slika 3�4�1 na strani 114)� Rezultati kažejo, da vzdolž Pivke, tudi Rak v Planinski jami ne, so v obdobju od septembra 2007 do marca 2009 saj tudi pri njem ne opažamo prevladujočega apnenčaste ploščice pridobile na teži, kasneje pa raztapljanja, na sotočju pa korozija mešanice izgubile (Slika 3�4�4 na strani 119)� Čeprav del ne prevlada nad izhajanjem CO2 iz vode in prirastka teže odpade na odlaganje organskih posledičnim skromnim odlaganjem sige� Na snovi iz deloma onesnažene vode, rezultati nekaterih merilnih mestih smo zabeležili kažejo na zanemarljivo intenziteto raztapljanja� korazijo, kar kaže na intenziven prenos talnega Na spodnjih apnenčastih ploščicah smo vseskozi materiala vzdolž podzemeljske Pivke� Čeprav bi zabeležili odlaganje (do 1 µm/a), medtem ko smo se lahko odlaganje odrazilo v sigovih prevlekah, raztapljanje na višje ležečih ploščicah zabeležili le tega nismo nikjer opazili� Je pa tudi res, da v dveh merilnih obdobjih, čeprav so bile ploščice nekatere tipične oblike raztapljanja (npr� fasete) poplavljene v vseh štirih merilnih obdobjih� kljub prisotnosti vzdolž podzemeljske Pivke ne Pojav raztapljanja je povezan z visokimi vodami kažejo recentne rasti (robovi med fasetami so Nanoščice, ki se lahko odrazijo v raztapljanju le obrušeni s strani korazije, na delu faset se pojavlja ob ustrezno nizki Pivki (Slika 3�4�5 na strani 120)� mrežasta struktura kalcitnih žil (t�i� boxwork)� Kljub temu so povprečne vrednosti raztapljanja Vse to kaže, da je bila Pivka v preteklosti bolj zelo skromne (največ -0,6 µm/a)� Zaradi visokega agresivna, ni pa raztapljanja zaznati danes deleža Pivke se niso agresivno obnašale niti (izjema so zgornji deli rovov, ki so v dosegu izredno visoke vode, ki so 12� decembra 2008 poplavnih voda)� 5.4 Splošni zaključki, diskusija in možnost nadaljnjih raziskav Metodologija uporabe apnenčastih ploščic v izjemni preciznosti Meritve kraških procesov zahtevajo uporabo (do ±0,05 µm) in točnosti metode (v povprečju posebnih metod merjenja, med katerimi velja ±0,2 µm, največje odstopanje ±0,4 µm)� Ne glede izpostaviti predvsem naslednje: mikrometrske na preciznost in natančnost, uporabo apnenčastih meritve, hidrokemična metoda in uporaba ploščic za meritve raztapljanja ali odlaganja sige apnenčastih ploščic� intenziteta kraških procesov spremljajo tudi nekatere pomanjkljivosti, ki se je običajno izredno nizka, zato je glavna prednost tičejo predvsem različnosti v litološki sestavi 141 Povzetek apnenčastih ploščic v primerjavi s kamnino, kjer primerjavi obeh metodologij in boljšemu se jama razvija (hitrost raztapljanja dolomita je poznavanju razlik, ki se med metodologijama lahko tudi 10-krat manjša v primerjavi z lipiškim pojavljajo� apnencem), ter sveže odrezano površino, ki je v tem pogledu precej različna od deloma preperele Intenziteta raztapljanja oziroma odlaganja stene jamskih rovov� Kratek interval meritev sige tudi zmanjšuje vpliv mikroorganizmov, ki imajo Na splošno je intenziteta kraških kemijskih lahko ključno vlogo pri hitrosti procesov zlasti procesov nizka, kar ustreza dolgotrajnemu takrat, ko je hitrost kraških procesov nizka� S razvoju kraških jam� Vzdolž naših največjih pogosto menjavo apnenčastih ploščic njihov podzemnih vodnih tokov lahko pričakujemo vpliv znatno zmanjšamo� Pri apnenčastih na dnu rovov odlaganje sige, višje navzgor pa ploščicah, ki so pritrjene z železnim vijakom, raztapljanje nekaj desetink μm na leto� Take lahko pričakujemo tudi znaten vpliv raztapljanja hitrosti so značilne tako za jame, ki jih napaja s strani rje, zato je v izogib temu problemu razpršen ali koncentriran dotok kraške vode nujna uporaba nerjavečega jekla ali plastike� (Križna jama, Križna jama 2), in celo za jame, ki Za točnejšo opredelitev uporabnosti metode odvajajo vodo z nepropustnih kamnin (v kolikor apnenčastih ploščic bi bile zelo koristne podobne je vodozbirno območje sestavljeno iz deloma meritve v drugih podzemskih okoljih� karbonatnih kamnin; Škocjanske jame), ter za Primerjava meritev z mikrometrom in jame, ki jih napaja kombiniran dotok kraške apnenčastimi ploščicami kaže, da je magnituda in nekraške vode (Postojnska jama)� Največja procesov v obeh primerih enaka, vendar je raz- intenziteta raztapljanja in njena prostorska lika v nekaterih primerih, npr� na začetku mer- variabilnost je značilna za območja, kjer prihaja itev, pri velikem odstopanju hrapavosti naravne do izrazitih neravnovesij v koncentraciji CO2 (npr� podlage od gladkosti apnenčastih ploščic in pri v Križni jami) ali neravnovesij v koncentraciji intenzivnejši rasti sige, kljub temu precej velika� Ca2+ ionov (npr� v jami Lekinka)� Tudi v takih Ne glede na to se resne napake lahko pojavljajo primerih je raztapljanje lahko intenzivnejše v obeh primerih, tako da zaenkrat ne moremo od -100 µm na leto, medtem ko se v jamah z trditi, katera metoda je bolj reprezentativna� Za odlaganjem sige iz jamskih potokov odloži več katero izmed njih se bomo odločili je odvisno od kot 100 µm sige na leto� Za podzemne vodne hitrosti procesov (uporaba mikrometra je prim- tokove, ki povezujejo kraška polja ali planote, erna le za jame z večjo intenziteto procesov, teh pa je poleg majhne intenzitete kraških procesov je razmeroma malo), pojava korazije (apnenčaste značilno majhno spreminjanje procesov vzdolž ploščice so neuporabne pri pojavu zmerne- podzemnega toka� To je najverjetneje posldeica močne korazije) in dostopnosti do merilnih mest velikega pretoka, ki ne omogoča intenzivnega (apnenčaste ploščice so zaradi enostavnejše upor- kontakta s povečano koncentracijo CO2 značilne abe primernejše za težje dostopna mesta)� za jamski zrak� Taki podzemni vodni tokovi so V izbranih primerih vodnih jam je hitrost običajno (pre)nasičeni s kalcitom že na ponorih, kraških kemijskih procesov običajno tako nizka, zato je zanje značilna celo majhna intenziteta da je uporaba apnenčastih ploščic nujna, v kolikor odlaganja sige (okoli 0,6 µm na leto)� izredno želimo v nekaj letih dobiti statistično pomembne majhna intenziteta raztapljanja je značilna rezultate� Kljub temu svetujemo nadaljnjo celo za visoke vode ali pa najbolj intenzivno pozornost pri uporabi apnenčastih ploščic, saj se raztapljanje niti ni značilno za najvišje pretoke� lahko pojavijo zaenkrat nepoznana odstopanja Zato ni presenetljivo, da so nekateri raziskovalci v od dejanske hitrosti kraških kemijskih procesov� nastanek jam z raztapljanjem dvomili (npr� Melik Več pozornosti bi kazalo posvetiti nadaljnji 1955), nekateri so to celo dokazali (npr� Oertly)� 142 Povzetek Presenetljivo je, da v raztapljanje ni dvomil procesov in njihovi prevladujoči smeri (raztapl-Gams, čeprav ga velikokrat ni mogel dokazati ali janje-odlaganje sige) na prehodu pleistocena v pa je bilo izredno šibko� Zato v njegovih člankih holocen� V hladnih obdobjih pleistocena lahko sledimo tendenco od trdne prepričanosti v tako pričakujemo manjše (ali celo odsotno) odl-raztapljanje jamskih vodotokov v 60-ih letih do aganje sige ter intenzivnejše raztapljanje� Vzrok postopnega nagibanja k neaktivnosti jamskih v preobratu podzemnih geomorfnih procesov vodotokov v 90-ih letih 20� stoletja� Majhna lahko najdemo v znatni spremembi temperature, intenziteta raztapljanja v epifreatični coni ki je spremenila vegetacijo, s tem produkcijo CO2 potrjuje dejstvo, da se daleč največja količina v prsti, manjšo koncentracijo CO2 v prenikli vodi karbonatov raztopi v epikraški in vadozni coni� in posledično manjšo intenziteto raztapljanja v Odnos med obema intenzitetama je z našimi vadozni coni� Zmanjša se tudi možnost izhajanja meritvami tudi kvantitativno dokazan� Pogost CO2 iz prenikle vode v dobro prezračenih vod-pojav v jamah je, da prezračevanje zmanjšuje nih rovih� Nižja celokupna trdota in manjša kon-koncentracijo CO2 v jamskem zraku (posledično centracija CO2 v prenikli vodi nujno privedeta tudi v vodi), s tem pa povečuje odlaganje sige do znižanja odlaganje sige ter pripeljeta k manjši celo iz jamskih vodotokov� verjetnosti odlaganja sige v jamskih rovih� Te Pri intenziteti kraških procesov je zelo slabo povezave so bile v preteklosti pogosto opazo-poznana vloga podzemskih mikroorganizmov, vane pri rasti kapnikov in lehnjakovih pragov, ki se jo lahko enostavno proučuje z različno zelo redko pa so mu pripisovali močnejšo vlogo pogostnostjo meritev v jamskih rovih� V kolikor pri širjenju jamskih rovov� Če posplošimo, bi so naša predvidevanja pravilna, je intenzivnejše moralo biti intenzivnejše raztapljanje značilno raztapljanje pričakovati pri nekajletnih za glaciale, manjše (oz� odlaganje sige) pa za in-izpostavitvah apnenčastih ploščic v primerjavi z teglaciale� To domnevo bi bilo lahko testirati v vsoto meritev v krajših merilnih obdobjih� današnjih subpolarnih razmerah� Kljub vsemu je potrebno opozoriti, da nižanje letne temperature Razmerje med današnjimi procesi, dejavniki ne pripelje vedno do povišanega raztapljanja, in oblikami npr� na ponorih visoko agresivne alogene vode� Eno izmed največjih presenečenj tekom meritev Presenetljivo je, da v jamskem sistemu Križna je prevladujoče (sicer po intenziteti majhno) odl- jama-Križna jama 2, ki se napaja s preniklo aganje sige v nekaterih hidrološko pomembnih vodo, nihanje pretoka nima odločilne vloge pri slovenskih jamah (Postojnski jami, Planinski intenziteti odlaganja sige in raztapljanja, ampak jami, Škocjanskih jamah, 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