HYDROGEOLOGY OF THE GÖKPINAR KARST SPRINGS, SIVAS, turkey HIDROGEOLOGIJA KRAŠKIH IZVIROV GöKPINAR, SIVAS, TURČIJA Fikret KA^AROGLU1 Abstract UDC 556.36:551.44(560) Fikret Kafaroglu: Hydrogeology of the Gökpinar karst springs, Sivas, Turkey Gökpinar karst springs are located 8 km to the south of the Gürün district centre, Sivas, Turkey. The springs have two main outlets (Gökpinar-1 and Gökpinar-2) and outflow from Jurassic-Cretaceous Yüceyurt formation (limestone). The total discharge of the springs ranges between 4.5 and 7.8 m3/s. The study area is formed of allocthonous and autocthonous lithological units whose ages range from Upper Devonian to Quaternary. These lithologies are mostly formed of limestones. Yüceyurt formation (limestone), from which Gökpinar karst springs outflow, constitute the main aquifer in the study area and is karstified. The unit has a well developed karst system comprising karren, dolines, ponors, underground channels and caves. The recession (discharge) analysis of the Gökpinar springs was carried out and the storage capacities and discharge (recession) coefficients of the Gökpinar-1 and Gökpinar-2 springs were calculated as 141x106 m3 and 98x106 m3, and 2.71x10-3 day-1 and 2.98x10-3 day-1, respectively. The storage capacities and discharge (recession) coefficients obtained suggest that the karst aquifer (Yüceyurt limestone) has large storage capacity, and drainage occurs very slow. The major cations in the study area waters are Ca2+ and Mg2+, and anion is HCO--. The waters are calcium bicarbonate type. Some of the water chemistry parameters of the Gökpinar springs range as follows: T=10.8-11.1°C, pH=7.65-7.95, EC=270-310^S/cm,TDS=170-200mg/L,Ca2+=40.0-54.0mg/L, Mg2+=4.5-10.0 mg/L, HCO3=144.0-158.0 mg/L. Temperature, EC, TDS, and Ca2+ and HCO3 concentrations of the Gökpinar springs did not show significant variations during the study period. Keywords: hydrogeology, karst, groundwater, Gökpinar springs, Sivas. Izvleček UDK 556.36:551.44(560) Fikret Kafaroglu: Hidrogeologija kraških izvirov Gökpinar, Sivas, Turčija Kraški izviri Gökpinar se nahajajo 8 km južno od regijskega središča Gürün, Sivas, Turčija. Voda izvira iz dveh glavnih izvirov (Gökpinar 1 in Gökpinar 2) in izteka iz jursko kredne Yüceyurt formacije (apnenec). Skupni pretoki nihajo med 4,5 in 7,8 m3/s. Prispevno območje pokriva alohtone in avtohtone litološke enote, katerih starost sega od zgornje devonskih do kvartarnih kamnin, večinoma apnencev. Formacija Yüceyurt (apnenec) sestavlja glavni vodonosni sistem in je močno zakrasela. Območje prekrivajo številne škraplje, vrtače, ponori, podzemni kanali in jame. V prispevku je bila izvedena analiza zmanjševanja pretoka na izvirih Gökpinar, izračunani sta bila količnika uskladiščenja in upadanja pretoka obeh glavnih izvirov. Količnik uskladiščenja je 141x106 m3 oziroma 98x106 m3, količnik upadanja pretoka pa 2.71x10-3 dan-1 oziroma 2.98x10-3 dan-1. Dobljeni rezultati kažejo, da ima obravnavani vodonosnik Yüceyurtskega apnenca veliko zmogljivost uskladiščenja in zato je odvodnjavanje precej počasno. Glavni kationi v vodah na obravnavanem območju so Ca2+ in Mg2+, med anioni pa prevladuje HCO-. Vode so kalcij-bikarbonatnega tipa. Nekateri kemijski parametri v vodah izvirov Gökpinar se gibljejo med naslednjimi vrednostmi: T=10.8-11.1°C, pH=7.65-7.95, EC=270-310^S/cm,TDS=170-200mg/L, Ca2+=40.0-54.0mg/L, Mg2+=4.5-10.0 mg/L, HCO3=144.0-158.0 mg/L. Temperatura, EC, TDS, Ca2+ in HCO-- koncentracije niso v času opazovanja pokazale značilnih variacij. Ključne besede: hidrogeologija, kras, podzemna voda, izviri Gökpinar, Sivas. 1 Mugla Sitki Ko^man University, Department of Geological Engineering, TR-48000 Mugla, Turkey, e-maü: &acaroglu@mu.edu.tr Received/Prejeto: 29.3.2010 INTRODUCTION Karst terrains in the world are mostly composed of carbonate rocks. About one third of Turkey is covered by carbonate rocks, and most of these rocks are karstified. Karst groundwater is a major water resource for many settlements (e.g. Antalya, Iskenderun) in the karstic regions of Turkey (Ka^aroglu 1999). Carbonate rocks (limestone, dolomitic limestone) cover a large area in the vicinity of Gürün, south of Sivas, Turkey. Karstification has developed in most of these rocks. High-yield karst springs outflow from these karstified lithologies. Karstification also occurs in the gypsum in the region extending from the west to the east of Sivas, Turkey, and there are some large capacity gypsum karst springs (Ka^aroglu et al. 1997, 2001). Fig. 3: Gökpinar-2 spring (Photo: F. Kagaroglu). Fig. 1: Location map of the study area. The water is used for fish production, power (electricity) generation and irrigation. This study was conducted to identify the hydrogeological and hydrogeochemical properties of the Gökpinar karst springs and karstic features of the study area. The study is the first hydrogeologi-cal investigation conducted on Gökpinar karst springs. Fig. 2: Gökpinar-1 spring (Photo: F. Kagaroglu). Gökpinar karst springs are located 8 km to the south of Gürün district centre, Sivas, Turkey (Fig. 1). The springs discharge the groundwater in the karstified Jurassic-Cretaceous Yüceyurt formation (limestone) and have two main outlets. Gökpinar springs (Gökpinar-1 and Gökpinar-2) form two ponds at the discharge points (Figs. 2 & 3). Fig. 4: Gökpinar stream (downstream of the Gökpinar springs, GD-1) (Photo: F. Kagaroglu). The study area covers an area of about 200 km2 which is drained by Gökpinar stream. Gökpinar stream (Fig. 4), mainly fed by Gökpinar karst springs, discharges into To-hma river (Fig. 5) which is a tributary of the Euphrates river. The Euphrates river and its tributaries constitute one of the largest trans-boundary river system in the Middle East and lie in Turkey, Syria and Iraq. Fig. 5: tohma river (upstream of the Gökpinar stream connection, TQ-1) (Photo: F. Kagaroglu). Field observations and mapping, discharge measurement on the streams and springs, water sampling and analyses were performed in order to achieve the purposes of the study. The flow measurement of the springs and streams were carried out by means of current meter. Temperature (T), pH, electrical conductivity (EC), and total dissolved solids (TDS) of the waters were measured at the time of the sample collection using portable (field-type) instruments. EC values were reported at 25°C. The measurement and analysis procedures given by APHA-AwwA-wPCF (1995) and Hem (1985) were followed during the field and laboratory work. The field work of the study were carried out between August 1995 and October 1996. geology The study area is located within the Eastern Taurid Belt (Kurtman 1978; Atabey et al. 1994). In the area alloch-tonous and autochtonous sedimentary, ophiolitic and volcanic rocks crop out. The geological ages of these rocks range from Upper Devonian to Quaternary (Fig. 6). The geological setting of the area is described in the following paragraphs based on the studies of Kurtman (1978), Atabey (1993, 1996) and Atabey et al. (1994). STRATIGRAPHY Allochtonous lithological units (Fig. 6) consist of Munzur limestone (Triassic) and Pinarba^i ophiolite (Jurassic- Fig. 6: Hydrogeological map of the study area (modified from Atabey et al. 1994 and Kagaroglu 2006). Cretaceous), whereas autocthonous units are Gümü^ali (Upper Devonian), Yüceyurt (Jurassic-Cretaceous), Demiroluk (Eocene), Govdelidag (Upper Eocene-Lower Miocene), Gürün (Miocene) formations and Alluvium (Quaternary). Munzur limestone (Mzm) is exposed in the eastern part of the area, and consists of medium-thick bedded, gray-white, yellowish coloured, fractured, partially karsti-fied limestone. The thickness of the unit ranges between 400-750 m. Pinarba^i ophiolite (Kp) crops out in a small area in the east, and formed of serpantine, serpantinized peridotite, piroxenite, harzburgite, dunite and gabro. Gümü^ali formation (Dg) crops out in the eastern part of the area. It consists of algae, gastropoda, echin-ide, brachiopoda containing thin-medium bedded limestone, and alternating shale, mudstone and thin bedded sandstone. The thickness of the formation ranges between 200-250 m. Yüceyurt formation (Jky) covers the largest part of the area. It comprises medium-thick bedded, grey-white, yellowish coloured limestone and dolomitic limestone at lower and middle parts of the sequence. The upper part of the unit consists of partially massive, white and pinkish coloured limestone. The unit is densely fractured, jointed and karstified. The thickness of the formation ranges between 400-1,100 m. The unit overlies Gümü^ali formation and is overlain by Demiroluk formation unconformably. Demiroluk formation (Td) is exposed at the central and southern parts of the study area. It comprises conglomerate, calcarenite, sandstone, limestone, marl and clayey limestone. The formation is divided into two members (Atabey et al. 1994) as Arpa^ukuru member (Tda) and Ba^oren member (Tdb). Arpa^ukuru member consists of thick bedded conglomerate, calcarenite, thick bedded and massive limestone. The thickness of the member ranges between 50-200 m. Ba^oren member is formed of alternating grey-greenish marl, thin layered calcarenite, clayey limestone, and very thick bedded (2-3 m) calcarenite and sandstone. The thickness of the member ranges between 200-400 m. Govdelidag formation (Tgd) crops out in a small area at the southeast of the study area. The unit is formed of red, thick bedded and massive conglomerate and in-terlayers of thick bedded (0.5-1.0 m) sandstone, and brown, yellow coloured mudstone. The thickness of the formation ranges between 200-350 m. The unit overlies Demiroluk formation and overlain by Gürün formation unconformably. Gürün formation (Tg), which was named by Kurt-man (1978) is exposed at the north and northwest of the study area. The unit consists from the bottom to the top of conglomerate, sandstone, calcarenite, marl, mudstone, tuf, tufite, marl interlayered thin layered clayey limestone and medium-thick bedded or massive limestone (Atabey et al. 1994). This rock sequence is crossed by volcanic rocks or contain their interlayers at some localities. These volcanic rocks comprise tracky andesite, andesite, tuf, aglomerate and lava, and were identified as Karadag member (Tgk) by Kurtman (1978). Tracky andesite has columnar and jointed structure. Alluvium (Qal) is exposed along the Tohma river and Gokpinar stream valleys. It consists of loose gravel, sand, silt, and clay. Locally clay lenses and cross-bedding is present in the alluvium. TECTONICS The study area is located in the Taurid Tectonic Belt (Kurtman 1978). The geological evolution of the region was completed between Upper Devonian and Quaternary. Pinarba^i ophiolite replaced over the carbonate rocks (Munzur limestone) during pre-Maestrichtian. Due to the compressional regime which initiated in Upper Paleocene period folds, overthrusts, strike slip and normal faults have developed (Fig. 6). Munzur limestone thrusted over autochtonous lithological units. The folds (anticlines and synclines) developed in Gürün formation strike in NE-SW direction. In Miocene N-S directed Sukati strike-slip fault formed, and crossed pre-Pliocene aged rocks (Atabey et al. 1994). The rocks in the study area have gained fractured and jointed character at different degrees depending on the lithological and physical properties. Jointed structure is apparent especially in limestones. KARST HYDROGEOLOGY KARST FEATURES Karst areas are characterized by the occurrence of the various type and size karst features and karst landforms. In the study area (Fig. 6), small scale solution sculpture and large scale karst landforms and features have developed mostly in the Yüceyurt limestone. Small scale solution sculpture consists of microkarren, karren, solution pits and solution pans. Large scale karst landforms in the study area are dolines (sinkholes), ponors (swallow holes), and closed depressions. Some caves were also observed in the study area. Karren are the most developed karst landforms in the study area. The dimensions of the karren range in general from a few centimeters up to 10 meters in length, and from a few centimeters to 1 meter in width and depth. Some karren chanels are filled by excess soil. They are dominantly of "rundkarren" type (Bogli 1980; Ford & Williams 2007) which have rounded cross section. On the Yüceyurt formation which mostly consists of thick bedded or massive limestone, karren form limestone pavements in some bare areas. The dimensions of the pavement areas in the study area extend up to a few hundred meters. Limestone pavements develop best upon thick to massive bedded strata where strata are flat-lying or gently dipping (Ford & Williams 2007). Alpine relief and climate particularly encourages bare-pavement karst, with joint enlargement (kluftkarren) and little soil cover (LaFleur 1999). Solution pits which are among the observed karst landforms in the study area have circular, elliptical or irregular plan view, and their diameter range from a few centimetres to several decimetres. Some pits are aligned, and located along the joints. Solution pans have flat or nearly flat bottoms, and are generally observed on bare rock. Dolines are among the karst landforms that give karst topography its particular character, and are caused by dissolution, collapse, suffosion, or subsidence processes. In the study area dolines are widely distributed karst landforms. The dolines in the study area which were probably caused by dissolution or collapse, are mostly distributed in the south and west parts of the area at high altitudes, and often follow structural trends and lineaments. They are usually circular to subcircular in plan view and have diameters ranging from a few meters to some hundred meters. Ponors (swallow holes) are the places where the water from allogenic sources inflows into karst aquifer and make important contribution to the karst ground-water recharge process. The water goes underground via a ponor as a sinking stream, concentrated recharge, or from ponded water. Ponors observed in the study area are generally located at the bottom or along the periphery of the closed depressions, along the fault and fracture zones, and along the stream beds. They have irregular or subcircular shape and the dimensions reach up to a few meters. Large scale closed depressions are scarse in the study area in comparison to the number of dolines. Closed depressions tend to be broad and shallow. Their length in the study area reach up to several hundred meters. KARST SPRINGS The groundwater flow system in the karst aquifer of the Gökpinar springs (Yüceyurt formation) is characterized by relatively uniform flow and reasonably uniformity of the hydrochemistry of the springs. In the study area two large capacity karst springs, named Gökpinar-1 (GK-1) tab. 1: Springs in the study area. (Fig. 2) and Gökpinar-2 (GK-2) (Fig. 3) springs, outflow from the Jurassic-Cretaceous Yüceyurt formation (Fig. 6 & Tab. 1). These springs constitute two main discharge points of the karstic aquifer, and are located on the boundary of the Yüceyurt and Gürün formations. There are also nine low yield (0.5 to 3.0 L/s) springs (Tab. 1) in the study area outflowing from Yüceyurt and Gürün formations (Kaq;aroglu 2001, 2006). Karst springs commonly appear at the contact between a carbonate-rock massif and low-permeability layers (Bonacci 2001). Gökpinar-1 spring (Fig. 2) is located in the east part of the study area. It outflows through the bottom of a funnel-shaped depression (approximately 100 m in length, 40 m in width), forms a "rise pond" (White 2002), with a maximum depth of 15 m, and discharges its water into Gökpinar stream via a channel. Discharge of the spring ranges between 2,415-4,425 m3/s (Tab. 1). Gökpinar-2 spring (Fig. 3) is located about 100 m to the west of the Gökpinar-1 spring and issues from the limestone aquifer through solution channels. The spring forms a pond (approximately 40 m in length, 15 m in width, and maximum depth is 2 m), and discharges its water into Gökpinar stream via a channel. Discharge of the spring ranges 2,175-3,395 m3/s. The discharges of the Gökpinar-1 and Gökpinar-2 springs does not have considerable variations between wet and dry months. This situation may be attributed to slow response character of the karst aquifer (Yüceyurt formation). In slow response aquifers the throughput time is sufficiently long to completely flatten the individual hydrographs, and a broad rise and fall relating to wet and dry seasons is observed (White 1999). Hershey et al. (2010) claimed that large and consistent spring discharges suggest a supporting groundwater system that is recharged over a large area where natural small-scale variations in recharge are smoothed. Spring no. Name of the spring Aquifer lithology (formation) Altitude a.s.l. (m) Discharge (L/s) Date of measurement GK-1 Gökpinar-1 Limestone (Yüceyurt fm.) 1,445 2,415 4,425 22.04.1996 16.07.1996 GK-2 Gökpinar-2 Limestone (Yüceyurt fm.) 1,450 2,176 3,395 31.10.1995 16.07.1996 GK-3 Serkiz Dere Limestone (Gürün fm) 1,920 1.0 04.08.1995 GK-4 Kale Dere Limestone - Clayey limestone (Gürün fm.) 1,890 3.0 04.08.1995 GK-5 Büyük gejme (Kavak) Clayey limestone (Gürün fm.) 1,820 2.0 04.08.1995 GK-6 Körpinar Limestone (Gürün fm) 1,880 2.0 04.08.1995 GK-7 Dönükpinar Limestone (Gürün fm.) 1,870 0.5 04.08.1995 GK-8 Kügükyazili Limestone (Gürün fm.) 1,880 1.0 04.08.1995 GK-9 Halacoglu Limestone (Gürün fm.) 1,850 0.5 04.08.1995 GK-10 Akpinar Limestone (Gürün fm.) 1,820 0.5 04.08.1995 GK-11 Velken Limestone (Yüceyurt fm.) 1,650 1.0 04.08.1995 A parallel trend exists between spring discharges and temperatures (Fig. 7). During high discharges, in general, the temperatures are also high. High values of discharge and temperature are observed during hot months. The water temperature of the Gökpinar springs ranges between 10.8-11.1°C, and variation is only 0.3°C. Based on Gürün meteorological station data (1973-1995), mean monthly temperature ranges between -3.5°C (January) Fig. 7: Variation of the discharge and temperature of the Gökpinar springs in time. and 21.4°C (July), and the mean annual temperature is 9.2°C. High water temperatures of the Gökpinar springs, greater than the mean air temperature, are likely to be the consequence of the groundwater circulation system within the karst aquifer. RECHARGE OF THE KARST AQUIFER In karst areas "localized recharge" (Lerner 1997; Hen-drickx & Walker 1997) type of groundwater recharge is generally dominated. During localized recharge, the water percolates rapidly into karst aquifer through cracks, fissures or solution channels (De Vries & Simmers 2002). In dry season, the recharge of the karst aquifer is much smaller. High-intensity winter precipitation is highly effective in enhancing recharge. During the wet season (between November and May in the Mediterranean region) 70-90% of the precipitation recharges the karst aquifer (Milanovic 1981). Hoetzl (1995) reported that on an exposed karst area in Saudi Arabia, 45% of the average rainfall disappears into sinkholes and corrosionally extended joints. Günay & Yayan (1979) calculated the infiltration percent of the precipitation as 45% for Kirkgöz karst springs (Antalya, Turkey) using discharges of the springs. The movement of the water through the karst aquifer depends upon matrix (intergranular), fracture and solution (conduit) permeability. In karst aquifers the water flow through the karst conduits is dominated. The karst aquifer in the study area (Yüceyurt limestone) is fed mainly from infiltration of the precipitation. The precipitation falling over the karstified limestone outcrops easily infiltrates through a great number of joints, fractures, solution channels, sinkholes, and ponors. In addition, there is indirect recharge from infiltration of temporary surface waters. The drainage of the Yüceyurt formation is almost entirely underground. The study area is located in a transition zone between typical semi-arid climate of Central Anatolia and Mediterranean climate. The climate is characterised by dry and warm summers and a cold and wet period that occurs during autumn, winter and spring. Precipitation distribution over the year is irregular. The monthly precipitation reaches a maximum during April and a minimum in August. Precipitation primarily occurs during cold seasons, and its distribution among the months allows a higher infiltration into the karst aquifer. The precipitation occurs mostly as snow during winter (December-March), which can have a significant effect on the recharge of the groundwater in the karst aquifer. According to Fiorillo (2009), in Mediterranean climates, the precipitation that occurs up to MarchApril of each hydrological year recharges karst aquifers, and subsequent precipitation, up to September-October, generally does not recharge the aquifers. In the flow systems of the carbonate rock province, recharge is commonly derived from precipitation in the mountains. The higher mountains receive larger amounts of precipitation and generate the higher portion of recharge (Hershey et al. 2010). The mean annual precipitation values of the meteorological stations in the vicinity of the study area range between 306 mm and 740 mm (Tab. 2). The precipitation generally increases with altitude of the station. Kandil, Sevdili and Adatepe stations are situated to the south of the study area and receive the precipitation mainly under the influence of the moist air front coming from Eastern Mediterranean Sea. The meteorological data of the above mentioned stations are limited and there is no meteorological station at high altitudes (above 1,500 m a.s.l.) in the vicinity of the study area. Hezanli Mountain (2,283 m a.s.l.) constitutes an important part of the Gökpinar Springs' recharge area which lies between 1,450 m and 2283 m a.s.l. The precipitation amounts recorded at meteorological stations tab. 2: Mean annual precipitations of the meteorological stations in the vicinity of the study area. Station name Operating organization Altitude of the station (m) Gauging period Mean annual precipitation (mm) Gürün DMi 1,250 1980-1995 306 Kandil DSi 1,280 1981-1995 411 Sevdili DSi 1,470 1981-1995 355 Adatepe DSi 1,330 1981-1995 740 tab. 3: Discharges of the Gökpinar springs (m3/s), and discharge coefficients (a) and storage capacities (\v) calculated from spring discharge hydrograph. Date of measurement Gökpinar-1 spring (GK-1) Gökpinar-2 spring (GK-2) Total of the GK-1 and GK-2 02.08.1995 3.015 2.650 5.665 29.09.1995 2.595 2.280 4.875 31.10.1995 2.295 2.175 4.470 22.04.1996 2.415 2.865 5.280 30.05.1996 4.025 3.200 7.225 16.07.1996 4.425 3.395 7.820 13.08.1996 4.225 2.925 7.150 27.09.1996 3.630 2.730 6.360 Average discharge 3.320 2.780 6.100 Discharge coefficient, a (day-1) 2.71X10-3 2.98X10-3 Storage capacity, Vs (m3) 141X106 (141,000,000) 98X106 (98,000,000) (Tab. 2) may easily increase by a factor of two or more at higher elevations of the recharge area. Because of the scarcity of the meteorological data, calculation of a complete water budget could not be performed. Fig. 8: Discharge graph of the Gökpinar springs (modified from Kagaroglu 2006). DISCHARGE OF THE SPRINGS The discharges of the Gökpinar springs, Gökpinar stream and Tohma river measured during the field work of this study are given in Tab. 3 and Tab. 4. In springs the minimum discharges were measured in September 1996 and October 1995, and the maximum in July 1996. The minimum discharge in Gökpinar stream is in October, and maximum discharge is in July. Gökpinar stream is mainly fed by the water discharged via Gökpinar springs. The upstream segment of the Gökpinar stream is an intermittent stream which is dry during a long period of the year. Gökpinar stream makes a great contribution to the discharges of the Tohma river (Tab. 4). Analysis of the spring recession hydrograph offers considerable potential insight into the nature and operation of the karst drainage system and provide information on the volume of water held in storage (Bonacci 1993). It also allows calculating the amount of the water drained through a particular spring from the beginning of the recession. These characteristics are important for evaluating water resources, especially in water deficient regions (Amit et al. 2002). The period after the spring rains, in some precipitation regimes, when the water input into the aquifer is practically zero (recession period) is the most suitable tab. 4: Discharges of Gökpinar stream and tohma river (m3/s). Stream/river/ measurement point Location of the measurement point Date of measurement Aug 1995 Sep 1995 Oct 1995 Apr 1996 May 1996 July 1996 Aug 1996 Sep 1996 Gökpinar stream GD-1 Downstream of the Gökpinar springs 5.665 4.875 4.475 5.410 7.275 7.820 7.155 6.060 Gökpinar stream GD-2 Su?ati-Upstream of the Tohma river connection 6.250 5.100 5.250 5.850 7.850 8.350 8.085 6.665 Tohma river ig-i Sugati-Upstream of the Gökpinar stream connection 0.950 1.510 1.815 6.905 3.180 2.570 1.925 2.245 Tohma river Tg-2 Sugati-Downstream of the Gökpinar stream connection 7.100 6.650 7.050 13.00 11.25 10.92 10.10 8.910 for this analysis (Milanovic 1981; Ford & Williams 2007; Bonacci 2001; White 2002). Maillet (1905) provided the first mathematical characterization of the baseflow recession. ttis interpretation is based on the drainage of a simple reservoir (Kovacs et al. 2005). In dry period, during which there is no water input into the aquifer, the dynamic water reserve in the aquifer from which the spring outflows decreases as a function of time, and the groundwater level declines. Maillet (1905) proposed that the discharge of a spring is a function of the water volume held in storage and described it by the simple exponential relation (Milanovic 1981; Ford & Williams 2007): Qt = Qo.e-«t or Qt = Qo.e-«(t-to) (1) where Q^ is the discharge (m3/s) at time t; Qo is previous discharge at time zero (to); t (or t-to) is the time elapsed (usually expressed in days) between Qt and Qo; e is the base of the natural logarithm; and a is termed recession (discharge) coefficient [T-1]. Maillet's (1905) equation recession analysis of the discharges of the Gökpinar springs (Tab. 3 & Fig. 8) were performed, and recession coefficients (a) and dynamic volume (storage capacity, Vs) of the aquifer were calculated. tte recession (discharge) coefficients of the Gökpinar-1 (GK-1) and Gökpinar-2 (GK-2) springs are aGK-1= 2.71x10-3 day-1 and aGK-2= 2.98x10-3 day-1, and dynamic volume (storage capacity) values are Vs(GK-1)= 141x106 m3 and 98x106 m3. s s(GK-2) tte value of the recession coefficient derives from the hydrogeological characteristics of the aquifer, espe- cially effective porosity and transmissivity. It represents the capability of the aquifer to release water. Small values of a indicate very slow drainage of the karst aquifer with a large storage capacity. tte springs of this type of aquifer are mostly permanent. Large values of a (the recession curve is steep) indicate rapid drainage of conduits and little underground storage (Milanovic 1981; Ford & Williams 2007). tte values of the recession coefficients calculated for Gökpinar springs and little changes in the discharge through the year indicate that the Yüceyurt limestone karst aquifer has a large storage capacity and the drainage occurs very slowly. tte discharge of the springs are not being directly affected by the monthly variations of the precipitation. Recession coefficients were calculated using Maillet (1905) approach for some large karst springs in Taurid Karst Belt (Turkey) by various researchers. ^elik & Af^in (1996) obtained a mean value of 6.92x10-3 day-1 for Kazanpinari karst spring in Elmali Polje, Antalya. Günay & Yayan (1979) calculated recession coefficients rangin from 3.1x10-3 day-1 to 6.2x10-3 day-1 for Kirgöz karst springs, north of Antalya. Yevjevich (1985) obtained a recession coefficient of 2.6x10-3 day-1 for Dumanli spring, Manavgat river basin-Antalya. Similar recession coefficient values of the Gökpinar springs and the above mentioned springs may be interpreted as karst aquifer of the Gökpinar springs (Yüceyurt limestone) has similar hy-drogeological characteristics that of the karst aquifers in the Antalya region. As mentioned before the study area is located in the eastern part of the Taurid Karst Belt. HYDROCHEMISTRY CHEMICAL CHARACTER OF THE WATERS Carbonate reactions are very important in controlling the composition of groundwater. Rocks made of car- bonates, such as limestones and dolomites, are often aquifers that have a high productivity. tte main minerals in these rocks are Ca- and Mg- carbonates which react tab. 5: Water analyses data of the Gökpinar springs. Samp. no. Date of sampling T (°C) pH EC (\iS/cm) TDS (mg/L) Cations (mg/L) Anions (mg/L) Hardness (mg/L CaCO3) Ca/Mg Na K Ca Mg CO3 HCO^ Cl SO. Sampling point: Gökpinar-l pring (GK-1) 1 02.08.1995 10.8 7.65 280 180 2.4 1.0 40.0 9.0 0.0 150.0 5.5 11.0 137 2.695 22 29.09.1995 11.0 7.90 295 190 2.3 0.9 46.0 8.5 0.0 153.0 7.5 12.5 150 3.281 32 31.10.1995 10.8 7.92 305 180 2.1 1.0 48.0 8.0 0.0 153.0 9.0 11.5 155 3.638 43 24.04.1996 11.0 7.80 310 200 2.6 1.2 50.0 6.0 0.0 150.0 5.5 16.5 150 5.053 52 30.05.1996 11.0 7.85 298 190 2.4 1.1 54.0 5.0 0.0 158.0 3.5 16.0 156 6.548 62 17.07.1996 11.1 7.75 270 180 2.2 1.0 48.0 4.5 0.0 147.0 5.0 12.0 139 6.467 72 13.08.1996 11.0 7.85 285 180 2.0 0.9 46.0 5.0 0.0 150.0 4.5 11.5 136 5.578 82 27.09.1996 11.0 7.85 280 180 2.1 1.0 48.0 6.0 0.0 145.0 5.0 13.5 145 4.851 Minimum 10.8 7.65 270 180 2.0 0.9 40.0 4.5 0.0 145.0 3.5 11.0 136 2.695 Maximum 11.1 7.92 310 200 2.6 1.2 54.0 9.0 0.0 158.0 9.0 16.5 156 6.548 Mean 11.0 7.82 290 185 2.3 1.0 47.5 6.5 0.0 151.0 5.7 13.1 146 4.431 Sampling point: Gökpmar-2 pring (GK-2) 2 02.08.1995 10.9 7.80 285 190 2.5 1.1 40.0 10.0 0.0 144.0 5.5 11.5 141 2.425 21 29.09.1995 10.9 7.95 307 200 2.3 1.0 44.0 10.0 0.0 153.0 7.5 12.0 151 2.668 31 31.10.1995 10.8 7.90 306 200 2.2 0.9 48.0 8.5 0.0 150.0 7.0 12.0 155 3.424 42 24.04.1996 10.9 7.65 310 200 2.5 1.3 50.0 6.0 0.0 150.0 5.5 16.5 150 5.053 51 30.05.1996 11.0 7.85 298 190 2.8 1.2 54.0 5.0 0.0 158.0 3.5 13.0 156 6.548 61 17.07.1996 11.1 7.90 285 190 2.4 1.1 50.0 6.0 0.0 153.0 3.5 12.0 150 5.053 71 13.08.1996 10.9 7.95 270 170 2.1 1.0 44.0 6.5 0.0 150.0 4.5 9.0 137 4.104 81 27.09.1996 10.9 7.95 285 180 2.3 1.1 50.0 5.0 0.0 147.0 5.0 14.0 146 6.063 Minimum 10.8 7.65 270 170 2.1 0.9 40.0 5.0 0.0 144.0 3.5 9.0 137 2.425 Maximum 11.1 7.95 310 200 2.8 1.3 54.0 10.0 0.0 158.0 7.5 16.5 156 6.548 Mean 10.9 7.87 293 190 2.4 1.1 47.5 7.1 0.0 151.0 5.3 12.5 148 4.056 easily with groundwater and give water its "hard" character (Appello & Postma 1996). The physico-chemical characteristics of groundwaters in karstic systems are determined by the lithology of the rocks that they cross, the physico-chemical processes that predominate, the residence time of water and the various conditions and modes of circulation that coexist within them (Lopez-Chicano et al. 2001). In order to identify the chemical character of the waters of the karst springs, field measurements and laboratory analyses were carried out on the water samples collected between August 1995-September 1996 (Tabs. 5 & 6). The waters of the Gökpinar springs and the other low yield springs are not rich (Tabs. 5 & 6) in major ions and total dissolved solids. Total dissolved solids (TDS) are moderate according to the classification proposed by Smith et al. (1993). The order of predominance of ions of the spring waters is Ca2+>Mg2+>Na+ for cations and HCO:>SO2+>a- for the anions. Ca2+ and HCO- are 3 4 3 dominant dissolved species in the waters of the Gökpinar springs and low yield springs due to the mineralogical composition of the karst aquifer. This also indicate the dissolution and precipitation of the predominant carbonate rocks in the aquifer. The mean values of the water quality parameters in Gökpinar-1 (GK-1) spring waters are as follows (Tab. 5): T=11.0°C, pH=7.82, EC=290 mS/cm, TDS=185 mg/L, Na+=2.3 mg/L, K+=1.0 mg/L, Ca2+=47.5 mg/L, Mg2+=6.5 mg/L, HCO3-=151.0 mg/L, a-=5.7 mg/L, SO2+=13.1 mg/L, Hardness=146 mg/L CaCO3. The mean values of the same parameters for Gökpinar-2 (GK-2) spring waters are 10.9°C, 7.87, 293 mS/cm, 190 mg/L, 2.4 mg/L, 1.1 mg/L, 47.5 mg/L, 7.1 mg/L, 151.0 mg/L, 5.3 mg/L, 12.5 mg/L, 148 mg/L CaCO3, respectively. In both springs these parameters and the amounts of the dissolved ions do not change significantly between wet and dry seasons. EC, TDS, and cation and anion concentrations of the Gökpinar springs have lower values which may be attributed to the short residence time of the water in the karst aquifer. The ranges of the water quality parameters of the low yield springs are as follows (Tab. 6): EC=270-435S/cm,TDS=180-230mg/L,Na+=1.4-4.2mg/L, K+=0.5-3.4 mg/L, Ca2+=38-60 mg/L, Mg2+=4.5-10 mg/L, HCO3-=134-198 mg/L, a-=3.5-10.5 mg/L, SOf=3.0-19.5 mg/L, Hardness=125-181 mg/L CaCO3. In a study of the carbonate springs in the central Appalachians, Shuster & White (1971) observed that d o ER u ugu ^ r n ni ipk ö G ni ps •TS a d yl an Q Ol a Ii Ol § C G e ht o pm d n K Ln \o O rs Ln rs CO O CO ^ '•O O CO CO ro CO ro rs rs ro Ln Ln Ln ro rs ro ro Ln Ln Ln cK cK cK cK cK c^ cK cK cK cK cK cK cK cK fO o Ln o CO ro rs \o CO CO CO Ln Ln CO ro ro CO uö 00 M^ Ln Ln ro ro Ln Ln ^ Ln Ln ro Ln r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ CO rs ro ro Ln ro Ln rs 00 CO rs CO r^ CO o Ln CO CO Ln c^ m m Ln ^ ^ Ln rs ro Ln ro ^ cp cp cp cp o cp cp Ln CO (N ^ Ln o ro Ln o Ln m c^ c^ ro c^ \o cS rs Ln CN CN CO Ln o O o cp cp o rs O ro o CO o o rs Ln Ln Ln Ln Ln rs o Ln MD Ln cS '— o o o o o t— t— "— cp O o o o cp o o cp o O cp o Ö o o Ln rs rs rs rs ro ro 'šT ^ \o ^ ["■v Ln m o o O CO CO o rs Ln o o ro m o O t— O O o O rs o O cp o cp cp cp cp o o O 00 Ln ^ o Ln ro CO ro \o ro Ln ro \o o o rs Ln ro rs ^ C^ ^ o rs CO Ln CO CO ^ ^ CO CO CO CO l-v r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ r^ Ln Ln Ln \o \o \o \o \o Ln Ln Ln \o \o \o \o \o c^ c^ C^ C^ c^ c^ c^ c^ "■N 00 ai Ö Ln K CO ai CO ai Ö Ln K CO ai o o o o O o o O o o o o o o o ai ^ ^ o K ro i< rs ai ^ ^ o K ro K o rs ro rs ro rs O rs ro rs ro ^ ^ rs ä^ l-N <3 ši rs r^ rs r^ rs r^ rs r^ U U U U u U U •O U «J (S a Ol rs rs ro rs rs rs rs rs rs ro Ln CO rs ro Ln CO C C conduit springs were very variable in hardness throughout of the year (coefficient of variation 10-24%). Diffuse springs had a rather constant hardness (coefficient of variation <5%). tte hardness of the Gokpinar streams do not show considerable changes in time. The coefficient of the variation of the hardness for GK-1 and GK-2 are 5.5% and 4.5%, respectively. Regarding the classification of the Shuster and White (1971) Gokpinar springs do not exhibit complete diffuse and conduit type character. Jacobson & Langmuir (1974) investigated the discharge and geochemistry of the carbonate springs in Fig. 9: Classification of the spring waters in the Piper diagram. central Pennsylvania. The researchers distinguished three types of karst springs as conduit, diffuse-conduit, and diffuse. The water chemistry data of the Gokpinar springs suggest that they are conduit type regarding to the EC values (EC 270-310 S/cm), and are diffuse type regarding to the coefficients of variation of the EC (4.8%) and discharge (26% for GK-1 and 15% for GK-2). tte discharges of the Gokpinar springs show larger variation than the other chemical variables. Jacobson & Langmuir (1974) explains such a situation by buffering effect on the water quality relative to discharge. Ca2+, HCO3- and hardness concentrations of the Gokpinar springs do not change markedly with time while Mg2+ concentrations exhibit significant change in time. On an equivalent basis (meq/L) Ca2+/Mg2+ ratios of the Gokpinar springs range from 2.7 to 6.6 for GK-1, and from 2.4 to 6.6 for GK-2 (Tab. 5). These ratios indicate mainly limestone dissolution and consistent with the fact that the springs issue from Yüceyurt formation which mainly consists of limestone and partially dolomitic limestone. tte Ca2+/Mg2+ ratio provides information on the rock type through which the groundwater has passed. tte Ca2+/Mg2+ ratio ranges from 1 to 1.5 for dolomite aquifers, and from 6 to 8 for limestone aquifers. Intermediate values indicate a dolomitic limestone or a mixed limestonedolomite sequence (White 1999). HCO-- is the dominant dissolved anion in the waters of the study area. HCO- concentrations of the Gokpinar springs varies between 144 and 158 mg/L. In low yield springs HCO- contents range from 134 to 198 mg/L. On an equivalent basis (meq/L), HCO3 accounts for 85% to 86% of the anions in Gokpinar springs and 83% to 86% of the anions in low yield springs. The high concentrations of HCO- in the water indicate intensive chemical weathering mainly carbonate dissolution occurring in the recharge area of the springs which is consistent with the lithological composition of the karst aquifer. The water analyses are presented in a Piper diagram (Piper 1944) (Fig. 9). The diagram represents the concentrations as percentages. Using this diagram the water analyses can be classified into types or hydro-chemical facieses (Back 1966). tte diagram displays the relations between rock type and water composition, and evolution of the composition along its route (Appelo & Postma 1996; Drever 1997). The water samples plotted near the left corners of the cation and anion triangles, and are rich in Ca2+ and HCO-. tterefore, with regard to the Piper diagram (Fig. 9), all waters are "calcium bicarbonate" type. Regarding the limits in Turkish Drinking Water Standards (TSE 2005) all spring waters in the study area are suitable for drinking. The recharge area of the Gokpinar springs is sparsely populated and there is no industrial, mining and agricultural activity that may cause water pollution. SATURATION STATE tte saturation indices (SI) describe quantitatively the deviation of water from equilibrium with respect to dis- ■iS (N Ln ro ro (N rs Ln \o C^ Ln (5 u^ o^ c^ 3C cK cK cK 00 cK cK cK c^ 00 S (N o o o CO CO fO Ln CO sä M^ M^ c^ c^ r^ fO r^ O _ ■Si CD ^ Ln ^ Ln (N c^ m \o Ln CO c^ C^ o^ c^ C^ cp cp cp cp cp CD cp o Q T? ^ Ln rs ro Ln rs O 'iš c^ c^ cp cp •■t^ (N Ln (N ro ro o d. oi ir e O rs rs ^ MD o^ C^ r^ cp ci cp CD cp cp cp CD CD 5 9 9 ru 1 ^ CO CO ro ro \o tsu ugu ^ CO Ln c^ O (N rN ro r^ ci cp CD cp CD A r of iasb fO Ln rs fO ^ fO ro ^ o ^ rN ro ra C^ c^ c^ c^ r^ uo -c ro r^ C ! ' ' ' ' ' k ö G e ht sg Ln Ln Ln Ln Ln Ln Ln Ln Ln H n ir rp s s s s s d O lei CD CD O O O CD CD CD O <3 ^ Q ol m o rf ^ sel C lp pma s (U J: