UDK 552.143 + 550.4 +628.54(285.2X497.12)=20 Lakes Bled and Bohinj Origin, Composition, and Pollution of Recent Sediments Franc Marcus Molnar Limnološka postaja Bled, Kemijski inštitut Borisa Kidriča, 61000 Ljubljana, Hajdri- hova 19, Jugoslavija Peter Roihe Abteilung fiir Geologie, Geographisches Institut der Universitat Mannheim, 6800 Mannheim 1, Schloss, B. R. Deutschland Ulrich Forstner Institut fiir Sedimentforschung der Universitat Heidelberg, 6900 Heidelberg 1, I m Neuenheimer Feld 236, B. R. Deutschland Janez Stern and Bojan Ogorelec Geološki zavod Ljubljana, 61000 Ljubljana, Parmova 33, Jugoslavija Alojz Ser cel j and Metka Culiberg Slovenska akademija znanosti in umetnosti, 61000 Ljubljana, Novi trg 3, Jugoslavija Abstract Fifteen grab samples and two shallow cores were studied from Lake Bled. Their carbonate contents are in the range 55—79 %. Calcite prevails but dolomite may occasionally amount up to 38 % of the carbonate compound. The non-carbonates seem mostly to be diatoms besides some quartz and traces of feldspar and clay minerals. Chemical analysis of the core sediments revealed a general increase of the heavy metals Zn, Cd and Pb in the uppermost layer. The highest content of Zn (up to 970 ppm) and Pb (up to 160 ppm) were found within nearshore grab samples thus indicating sewage input. The increased eutrophication of Lake Bled is evident. Eight grab samples and one core from Lake Bohinj are also carbonate rich sandy silts and clays with total carbonate contents ranging from 53—91 %. Calcite prevails especially in the western part of the lake. Dolomite content is, in the average, higher than in Lake Bled. The non-carbonates seem essentially similar to the Bled sediments. The core samples contain an increase of the heavy metals Zn, Cu, and Pb within the uppermost 10 cms. In addition, Fe-, Mn-, Cr-, and Ni-contents are unusually high compared to Bled. Kratka vsebina V poročilu so prikazani začasni podatki o sedimentoloških in geokemičnih parametrih iz raziskav sedi men tov v Blejskem in Bohinjskem jezeru. Iz Blejskega jezera smo preiskali vzorce 15 zajemov s površja jezerskega dna ter dveh jeder sedimenta do globine 45 cm. V sedimentu prevladuje karbonatni glinasti melj, ki vsebuje v zgornjih 10 cm pod površjem obilo organskih snovi. Zaradi menjavanja organskih in anorganskih sestavin je sediment laminiran. V preiskanih vzorcih je znašala celokupna količina karbonatov 55 do 79 %; bistvenih razlik med vzorci s površja in iz globine ni bilo. Prevladuje kalcit, vendar vsebuje ponekod karbonatna frakcija do 38 % dolomita. Med nekarbonatnimi sestavinami prevladujejo skeleti diatomej, v manjših količinah pa so zastopani še kremen, glinenec in minerali glin. Karbonatni sedimenti Blejskega jezera so v glavnem de-tritičnega izvora, saj sestoji tudi okolica jezera večidel iz triadnih karbonatnih kamenin. To velja predvsem za delež dolomita v sedimentu, medtem ko za kalcit ne moremo izključiti možnosti avtohtonega nastajanja ob udeležbi vodnih rastlin. Kemične analize jedrskih vzorcev kažejo splošno povečane količine cinka in kadmija, posebno pa svinca v zgornjih centimetrih profilov ponekod do 160 ppm. Najvišje koncentracije Zn in Pb smo našli v vzorcih sedimenta blizu obale, kar kaže na dotoke odpadnih voda. S tem v zvezi je postajala jezerska voda vedno bolj eutro-fična. Iz sedimenta Bohinjskega jezera smo preiskali vzorce 8 zajemov z jezerskega dna in eno jedro. Tudi v tem jezeru sestoji sediment v glavnem iz karbonatnega melja in gline. Vsebuje 53 do 91 % karbonatov; med njimi prevladuje kalcit, vendar je ponekod v karbonatni frakciji dolomita do 69 %. Količine dolomita v sedimentu Bohinjskega jezera so v celoti višje kot v Blejskem jezeru. Dolomit je nedvomno detritičnega izvora To velja tudi za glavni del kalcita, vendar domnevamo, da je tudi v Bohinjskem jezeru del kalcita avtohton. Nekarbonatne sestavine sedimenta obeh jezer se ne razlikujejo bistveno. Kemične analize jedra kažejo, da količine Zn, Cu in Pb v zgornjih centimetrih sedimenta postopno naraščajo. Pelod v jedrih sedimenta iz Blejskega in Bohinjskega jezera kaže, da so usedline v obeh profilih relativno mlade in niso starejše od 400 do 500 let. Z usammenf assung Es wird iiber vorlaufige Ergebnisse einer Untersuchung der Sedimente aus den Seen von Bled und Bohinj in Slowenien (Jugoslawien) berichtet; dabei werden sedimentologische und geochemische Parameter diskutiert. Funfzehn Greiferproben und zwei kurze Sedimentkerne mit einer max. Eindringtiefe von 45 cm wurden aus dem Bled-See untersucht. Es handelt sich um karbonatreiche Silte und Tone, in deren oberflachenna-hen 10 cm organtsches Material hSufig auftritt; ent&prechend dem Wech-sel von mineralischen und organischen Komponenten sind sie im mm-Bereich laminiert. Der Gesamtkarbonatgehalt der untersuchten Proben reicht von 55 bis 79 %, wobei keine wesentlichen Unterschiede zwischen Oberflachenproben und Kernproben bestehen. Es Uberwiegt Calcit, doch kann die Karbonatfraktion gelegentlich bis zu 38 % Dolomit enthalten. Die Nicht-Karbonate sind iiberwiegend Diatomeen-Skelette; ausserdem treten gennge Mengen an Quarz, Feldspat und Tonmineralien auf Die Karbonatsedimente in Bled-See sind im wesentlichen als detritische Bil-dungen aufzufassen, da die Umgebung des Sees aus Karbonatgesteinen von meist triassischen Alter besteht. Dies gilt insbesondere fur den Dolomitanteil, wahrend beim Calcit eine autochthon« Bildung unter Mitwirkung von Wasserpflanzen nicht ausgeschlossen werden kann. Die chemischen Analysen an den Sedi men tkernen erbrachten einen allgemeinen Anstieg der Schwermetalle Zink, Cadmium und besonders Blei, der sich in den obersten Profilzentimetern vollzieht, wobei Bleigehalte von z. T. 160 ppm erreicht werden. Die hochsten Konzentrationen fur Zink und Blei wurden in den ufernahen Proben gefunden, was auf abwasserhaltige Zuflusse hinweist Im Zusammenhang damit muss auch die beobachtete Zunahme der Eutrophierung des Sees gesehen werden. Aus dem Bohinj-See wurden acht Greiferproben und ein Sediment-kern untersucht. Auch in diesem See handelt es sich im wesentlichen um karbonatreiche Silte und Tone mit Gesamtkarbonatgehalten von 53 % bis 91 %. Dabei iiberwiegt im allgemeinen Calcit, doch wurden in Ein-zelfallen Dolomitgehalte bis 69 % der Karbonatfraktion angetroffen. Ins-gesamt sind die Dolomitgehalte des Bohinj-Sees hoher als die von Bled. Dolomit ist eindeutig detritisch und wird durch die Zuflusse in den See transportiert. Dies gilt auch fur die Hauptmenge des Calcits, obwohl auch dafiir ein geringer Anteil durch autochthone Bildung vermutet werden kann. Die Nicht-Karbonate unterscheiden sich nicht wesentlich von de-nen der Bled-Seesedimente. Die chemischen Analysen der Kernsedimente ergaben einen annahernd kontinuierlichen Anstieg der Schwermetalle Zink, Kupfer und Blei innerhalb der obersten Zentimeter zur OberflSche hin. Palynologische Untersuchungen zweier Bohrkerne von Boden der Seen von Bled und Bohinj haben gezeigt, dass die Ablagerungen, die zwei Bohrkerne erfassen, ziemlich jungen Alters sind, nicht alter als 400 bis 500 Jahre. Contents 1. Preface............................ 2. Limnological features of Lakes Bled and Bohinj...........96 3. Geological setting of the surroundings of Lakes Bled and Bohinj.....103 3.1. Lake Bled.........................JJJI? 3.2. Lake Bohinj....................... 3.3. Pleistocene lacustrine chalk from the surroundings of Lake Bled .... 104 3.4. Sediments of the streams flowing into Lakes Bled and Bohinj.....104 4. General properties of the sediments taken from Lakes Bled and Bohinj ... 107 4.1. Sampling methods......................107 4.2. Field description......................}07 4.3. Grain size distribution....................110 5. Pollen contents in sediments from Lakes Bled and Bohinj........112 5.1. Bohinj BH-5B.......................J}* 5.2. Bled BL-15B........................114 6. Mineral association in sediments from Lakes Bled and Bohinj......1J5 6.1. Introduction........................ 6.2. Analytical procedure.....................J J* 6.3. Lake Bled........................JJ* 6.31. Grab samples......................JJj? 6.32. Core samples...................... 6.33. Origin of the Lake Bled sediment..............ijJ 6.4. Lake Bohinj........................ 6.41. Grab samples......................JjjJ 6.42. Core BH-5B......................}jj| 6.43. Origin of the Lake Bohinj sediment............J 6j5. Autochthonous formation and dissolution of calcite within Lakes Bled and Bohinj........................J 29 6.6. Sedimentation rates....................... 7. Geochemistry of recent sediments from Lakes Bled and Bohinj......145 7.1. Introduction........................J™ 7.2. Analytical methods.....................14b 7.3. Interpretation of metal data..................146 731. Mean values......................................146 7.32. Core profiles................... * * 147 7.33. Inter-element relations...............! ! 150 7.4. Human effects on the metal composition of sediments from Lake Bled . 151 7.5. Metal contents associated with the lake carbonate sediments.....151 8. Summary and conclusions....................160 9. Acknowledgements.......................161 10. References............................ 1. Preface The quality of waters in many regions has greatly suffered as a result of the increasing impact on our environment by waste materials from industries, communities and agriculture. This development is especially conspicuous in a great number of fresh water lakes, that not only serve as drinking water and nutrient sources, but have a very high value for recreation purposes. Examples from all parts of the world have shown that lakes are very sensitive ecosystems that can be destroyed within a period of mere decades, and can then be regenerated only with very strenuous efforts. Meanwhile ambitious, large-scale research programs have been introduced at several locations in order to evaluate the causes, extent and future consequences of the pollution, and to prepare appropriate counter measures. In this respect, the investigation of sediment has become increasingly important, since the distribution of pollutants that are only sparingly soluble is, both in their spatial and temporal development, relatively easy to ascertain from such sediment deposits. An example is the research program begun in 1975, for heavy metal distribution in the Sava catchment area in Slovenia, above all in the sediment in the heavily polluted Moste dam, for which the first research results have recently been published (J. Stern and U. Forstner 1976). In the scope of a long-term cooperation between the Geološki zavod Ljubljana and the Institute for Sediment Research of the University of Heidelberg/Dept. of Geology, University of Mannheim, detailed sampling of sediment from Lakes Bled and Bohinj and their affluents was carried out in late summer 1976, in order to be able to more closely examine various aspects of the sedimentologi-cal and geochemical conditions of these lakes (see figs. 1, 2 and 3). The results of the team investigations are presented in six chapters relating to the different consideration aspects. 2. Limnological features of Lakes Bled and Bohinj Franc Marcus Molnar The Alpine lakes of Bled and Bohinj in Upper Carniola are characterized by two different environmental conditions. The latter is pure enough to maintain a natural biological equilibrium as the Savica River supplies it with water and air. Conversely, the ecological relations of Lake Bled are disturbed to a degree demanding a restoration. To overcome the lack of a natural aeration, a flushing project has been accomplished introducing a part of the Radovna River water through a pipeline into the lake (M. Rejic, 1973). The water pipeline went into operation in 1965, and since then the annual inflow of fresh water has been approximately 0,5—17 mio m3. In 1973 a permanent control of the lake started with the foundation of the Limnological station Bled, which was in 1974 incorporated into the Kemijski inštitut Borisa Kidriča Ljubljana. The lake remains eutrophic in spite of the flushing. The reason could be either that the amount of exchanged water is too small, or that the loading with phosphorus and nitrogen is too high. Neither excludes the other. Figures 4 and 5 show the variations of the oxygen content as well as temperatures and Secchi disc transparency in vertical water profiles at the two deepest points BL-1B and 15B of Lake Bled (fig. 2) during the year 1976. It is evident that in the summer and fail periods the hypolimnion remains anaerobic. There are eumictic or even dimictic periods. The temperature of the cool hypolimnic layer increases due to the inflow of the slightly warmer Radovna river water. An increase of some 3 °C influences the autumn and spring turnover. The lake is becoming holomictic. This can be dangerous for the consumption of oxygen. The Secchi disc transparency is smaller in winter when Oscillatoria rubiscens rises to the upper, cooler water layers. Limnophysical and limnochemical data from Lake Bled was obtained from vertical profiles at the same points BL-1B and BL-15B on September 28 and September 30, 1976 simultaneously with sediment sampling. A concentration of 7 — Geologija 21 •1 2 03 a 4 a 5 Fig. 2. Lake Bled and surroundings. Sampling sites 1 Grab sample 1 , , sediment 3 Fluvial sediment 2 Core profile ) lalie sediment 4 Rock sample 5 Glacial lacustrine chalk • Grab sample") o Fluvial sediment A Glacial lacustric chalk > lake sediment ^ Core profile J Rock sample Fig. 3. Lake Bohinj and surroundings. Sampling sites Fig. 4. Lake Bled, vertical profile at point IB Diagram showing the oxygen saturation, temperature and transparency dependent on the artificial flushing, during 1976 LAKE BLED Vertical profile at point 15 B 19 7 6 H « nI h I inflow (mM [ flushing ) Inn300 »0*700 H HI IV VI VII VIII IX XI XII 02"Sal (mg/11 «-« El*-18 Qt-s I I 3 E X s 5 i X o CO v ! a E 0S0000000S8— 0000000000000 CNCJONCOcocomaj - r> o- C-J OOLOOOOOOOOOOO N O O «0 -O >00 — >0^. CJiCOCOfSCNfNCNCNfN'— {NCO O £ » + + + COCOflONNNNNNNNN >0 O O o O O CN V v v OOCN^-OCOCO — CNO-OCOrs. oon-ocoooio>o«-nN — — — — C*4CMO _ _ lOmD-^iOiONO^OCO NNOMNaoOOrtOOO« coc8»o>»o>i>o>oooNn S0000008SSS8S OOOOOOOOOOOOO S 3 8 S S S 8 8 3 3 S £ 3 OOOOOOOOOOOOO lomiooioiowioiftirtioioio OOOOOOOOOOOOO • 1 • • • • •• •• »It OOOOOOOO^— ,_ -O ^ , , , • ••••••••«1 i i Nr-^O-fl^OOOO a iou tflttnONNinOOMrtBN ............ , •O-OiflflOtNOOOMDCO S-6 o J £ e CN UJ > S E X E u e O -r U fi X O r> E C*J v. Ž > O E Q_ E U DO S- E O O O O O O COOOOOOOO ^(o-ocon^o-io«" 8 0000iOir)U">if>OirtQOO ODOOOors.ivrs.rs.rs.r'viN.rs.rs.rs.'O'O O fN (N 'T ^ •OCO. ' ^' .'..' p ■. ■. 1 BLEJSKO JEZERO-15B cm On 5-10-15-20-25-30-35-40 45 o ° B C 0 20 40 60 80 100% 0 20 £0 60 80 100% o-Br BOHINJSKO JEZERO-5B ABC cm o 5 tO 15 20 25 30 dGy mGy IGy GyW „ . • dGy t,' ° o . • • • dGy • 0 20 A0 60 80 )00% 0 20 40 60 80 100% A. LITH0L0GY clayey silt sandy silt abundant organic remains lamination chalk-like sediment f semiliquid soft , stiff plant rests consistency s soft b " Gy G B Br W d m I gray green black brown white dark medium light B. GRAIN SIZE < 2 |im E^l 2 - 6.3 nm 6.3 M- - 20^m 20 - 63|im >63p.m C. MINERALOGY dolomite '////A calcite noncarbonate ingredient 4.22. Core samples The sediment was cored at points BL-1B and BL-15B in Lake Bled (see fig. 2) and at the site BH-5B in Lake Bohinj (see fig. 3). The thickness of sediment penetrated is 25—45 cms. The top (0—1.5 cm) of the two Bled cores is brownish and dark greenish gray liquid and slimy sediment, having an apparent waste odor. The sample BL-1B had at first a characteristic odor, releasing bubbles of hydrogen sulfide. Subsequently a repulsive sewage smell remained. Proceeding downwards in core BL-1B a brownish shaded sediment prevails showing a semiliquid jelly consistency which passes over into a sludge with cloddy inclusions. At a depth of 15—25 cms these inclusions gradually tend to increase. Simultaneously the colour changes into reddish brown and more and more the sewage smell increases. Noteworthy is the laminar structure at a depth of 3—7 cms. As to the core BL-15B, no difference occurs in its composition and consistency compared to BL-1B. They differ in colour only. From the depth 1.5 cm the sediment of the BL-15B becomes gray and greenish gray. In the interval 10—20 cms a bluish shaded sediment occurs and at a depth from 20 to 40 cms brownish spots are observed. The laminated interval is somewhat thinner there: it occurs at a depth of 2—3 cms. The core BH-5B from Lake Bohinj differs widely from those from Bled. First of all the Bohinj sediment contains fairly more sandy and silty fractions; therefore its water content is lower. Furthermore its fine-grained organic admixture is low. It abounds, however, in leaves. On the contrary the Bled sediment contains no remains of leaved plants. In general the Bohinj sediment is medium gray. At a depth of 5—7 cms a grayish white chalk-like intercalation occurs. The samples obtained possess no particular odor. 4.3. Grain size distribution Sieve and sedimentation analysis has been undertaken to determine the particle-size distribution in the sediment from lakes Bled and Bohinj (see tables 7, 8 and 9). A total of 54 samples were examined. After the preparation of the sample with water, each sample was sieved wet through the sieve screen, 0.063 mm DIN 4188. The oversize was dried at 105 BC and the undersize at 60 °C. Subsequently a part of the undersize < 63 /zm was dried at 105° C for sedimentation analysis. The majority of the samples were examined using the Sartorius sedimentation balance. For the core samples the sedimentation vessel after An-dreasen-Borner was used (table 9). The grain size variation in bottom sediment is shown in figure 9. In comparison with Lake Bohinj the sediment from Lake Bled is more finegrained and well sorted in both vertical and lateral directions. The grab samples from the depth 5—10 cms, as well as the core samples from the same depth, contain about 95 per cent particles < 20 /« 22-y <2 9'oinsi- of£in,I- __ill®-fli- ze om ze <63 urn weigh t per ce n t la 8.75 lb 0.55 2a 6.54 2b 0.86 3a 4.63 3b 0.89 4a 5.68 4b 3.41 5a 5.68 5b 1.58 6of7a 19.30 61* 7b 3.69 8c*b 16.90 9aM0a 20.97 9b 2.34 10b 4.49 11a 17.81 lib 1.50 I2afb 13,94 13a 7.22 13b 5.13 14a 13.91 14b 4.40 15a 22.86 15b 10.86 23.75 33.50 7.90 37.09 11.05* 35.76* 4.73 30.83* 14.20 40.56 5.27 35.34 21.07 26.54 3.58 41 .61 21.56 36.58 13,09 28.23 18.04 26.60 24.58 21.48 26.60 19.50 12.64 27.31 7.59 36.01 2.53 38,09 16.17 28.38 7.33 38.27 5.96* 24,50* 14.90* 22.66* 7.27* 31.58* 11.44 29,75 5.08 33,03 12.32* 32.82* 3.04* 29.80* 13,00 21.00 21.16 33.30 20.46* 26.19* 19.54* 44.04* 21,50 19.11 17.40 41.10 21,47 25.24 28.09 23.31 21,02 15.16 24.59 32.51 14.28 21.78 18.75 31,50 14.50 22.50 17.08 22.00 25.20 28.86 30.98 23.91 16.14 21.50 31.20 21,70 7.20* 48.40* 6.69* 48.53* 21.72* 34,30* 19.41 25.49 27.29 30.20 19.26* 12.74* 16.40* 39.90* 10.0 2.46 5.2 2.50 6.0* 2.40 2.6* 2.48 9.0 1.54 4.2 2.52 7.3 2.51 5.7 2.54 9.0 2.54 4.7 2.56 10.1 2.59 5.9 2.59 12.0 2.53 9.7 2.50 5.3 2.51 4.9 2.50 12,0 2.52 5.6 2,55 2.5* 2.45' 2.5* 2.50' 4.2* 2.53' 8.8 2.55 4.5 2.47 12.1* 2,41' 3.8* 2,50' Data obtained by the sedimentation balance and by the Andrea-sen-Borner* sedimentation vessel Table 8. Grain size data of the grab samples taken from the depth (a) 0—3 cms and (b) 5—10 cms from the bottom of Lake Bohinj Sample Nr. G rai n size i n pm Medium grain size ^jm Sp.gravity of grain size <63 pm >63 20-63 6.3-20 2-6.3 <2 wei g iht percent latb 21.82 13.30 19.30 13.70 32.05 7.9 2.28 2a 10,32 8,10 24.33 20.15 37.10 3.9 2.55 2b 7,06 7.42 18.72 17,80 49.00 2.3 2.52 3a 11.42 5.66 20.24 27,68 35.00 3.8 2.51 3b 6.84 4.00 17.36 16,00 55.80 1.8 2.50 4a 7.71 15.70 18.63 17.96 40.00 3.8 2.56 4b 5.92 12.98 23.50 14.60 43,00 4.0 2.55 5 (see: core samples 5 B) 13.2 2.61 6a 16.90 22.09 22.96 17.55 20,50 6b 10.20 30.10 19.20 10.70 29.80 9.1 2.63 Data obtained by the sedimentation balance Table 9. Grain size data of sediment samples from core profiles of Lakes Bled and Bohinj Depth in cms. Groin s i ze in p m Medium groin size ym Sp. gravity of grain size <63 fjtn >63 18-63 20-63* 5-18 6.3-20* 2-5 2-6.3* <2 weight percent blejsko jezero - Core 1 I 3: 0-5 19.10 1,07* 27.05* 9.48* 43.30 4.9 1.58 5-10 11,81 2.80* 17.79* 25.65* 41.95 3.8 2.58 10-15 4.12 6.11 31.82 10.38 47.57 3.0 2.47 15-25 6.37 7.85 37.62 6.67 41,49 5.6 2.49 blejsko jezero - Core 15 b: 0-5 16.13 2.74* 26,85* 16.01* 38.27 5.3 2.54 5-10 9.83 4.24* 21.72* 22.76* 41 .45 4.1 2.54 10-15 4.68 2.46 29.38 17.76 45*72 3.1 2.54 15-20 7.42 6.50 23.92 12.55 49.61 2.0 2,51 20-25 3.23 6.89 34.05 9.42 44.41 3.1 2.52 25-30 5.06 4.95 34.54 7.73 47.72 2.8 2.50 30-45 1.88 4.94 29.18 8.19 55.81 1.8 2.51 bohinjsko jezerc 1 - Core 5 b: 0-5 24.19 9.88* 20.70* 10.00* 35.23 8.1 2.63 5-10 12.78 10.02* 21.09* 16.79* 39.32 4.8 2.61 10-15 18.31 12.00 15,50 9.02 45.17 3.6 2.53 15-20 19.26 16.02 18,40 3.22 43.10 7.0 2.61 20-25 19.26 14.45 18.50 4.78 43.01 6.0 2.63 25-30 10,00 17.97 17.35 11.52 43.16 3.7 2.58 30-35 19.08 16.52 17.43 4.02 42.95 6.4 2.61 35-40 4.24 8.31 27.07 7.00 53.38 1.9 2.58 40-45 7.64 18.61 19.22 4.71 49.82 2.0 2.54 Data obtained by the Andreasen-Borner sedimentation vessel 5. Pollen contents in sediments from Lakes Bled and Bohinj Alojz Sercelj and Metka Culiberg Samples for pollen analysis have been taken and analyzed from the cores BL-15B and BH-5B at an interval of 5 cm. The main purpose of this investigation has been to gather some information about the paleoecology of the surroundings of the lakes and about the age of the sediments on the base of well known stages of vegetational development or special plant indicators of man's activity (A. Sercelj, 1971, 1975). Complete pollen analyses reveal about 50 taxa represented in different spectra. Since it is evident that not all plant taxa have equal meaning in interpreting vegetational history and hence stratigraphy, only the characteristic ones have been picked out (figs. 10 and 11). As they are different from each other, th* explanations of each are given separately for the most important points. BOHINJ BH- 5B 5.1. Bohinj BH-5B The pollen curves of various forest trees follow different, partly opposite courses. But the most characteristic ones are those of Pinus, Fagus and Ptcea. The Pinus curve increases from an initial 15 %> to 50 °/o on the top of the diagram, meanwhile the Fagus curve decreases in the same direction from 30 Vo to 5°/o tree pollen. This peculiar change in vegetation is certainly not due to climatic events. Originally this valley had been covered by woods of Abieti-Fagetum (depth 45—35 cm), and on the mountain slopes intermixed with fairly high percentages of Picea. Then cutting of beech forests for burning charcoal, used in melting iron, started, especially during the Middle Ages. This could be the point of decline of Fagus pollen curve. On the contrary, continuous rise of the pollen curve of Pinus suggests that the destroying of deciduous forest has continued by grazing, especially in the subalpine belt. The presence of Secaie pollen, other cereals, and of Cannabis-Humulus, though in low percentages, also indicates that the radical change in vegetation is due to extensive land use for farming. Selaginella selaginoides, the subarctic small fern, is present in relatively high percentages, though it did not thrive in the valley, but on the deforested mountain plateaus. 8 — Geologija 21 BLED BL-15B 5.2. Bled BL-15B The surroundings of Bled is a more opened landscape and there are no steep mountain slopes within the immediate neighbourhood. As a result the forest picture, as shown by the pollen diagram, is a little more intricate. The pollen diagram reflects two declines of the natural forest (Abieti-Fage-tum). The curve of Fagus shows two oscillations which are not very pronounced, with a decreasing tendency. Opposite to that of Fagus, the Pinus curve rises up to 23 %. Pinus forests are to be regarded here as a pioneer vegetation on previously highly degraded soils. More indicative about the general aspect of landscape may be the unusually high percentage of Juniperus (juniper) pollen in the middle of the diagram. This indicates heavy sheep grazing, juniper being the only resistant element. Direct indicators of man's activity are: Juglans (walnuttree), present with relatively high pollen values, obviously having been much cultivated here. High pollen values of Secale and other cereals, besides Humulus and Cannabis, which theoretically could have been cultivated here since eneolithic times, suggest that this country had been densely settled. There are two more cultivated plants that yield us also a reliable dating: Fagopyrum and Zea. Buckwheat has been introduced to Europe from Asia and reached this country about 1490, and corn has been brought to Spain in 1519. There is no doubt that this profile cannot be older than 500 years, but could be younger. 6. Mineral association in sediments from Lakes Bled and Bohinj Peter Rothe 6.1. Introduction Lake sediment consists of components of detrital, chemical, or biogenic origin. Within most lakes more than one of these components are found. It has been amply shown that many factors such as climate, geographical position, geological conditions, etc. are influencing the final composition of lake sediment. Carbonates within lakes may either be of detrital origin or they are formed authigenically within the lake due to biological activity, chemical conditions, or both. The surroundings of both Lakes Bled and Bohinj (Blejsko jezero and Bohinjsko jezero) consist almost entirely of limestones and dolomites of Permian and Triassic age. The aim of this chapter is to provide a preliminary description of the sediments within both lakes. The main part of these sediments has a clearly detrital origin. Carbonate mud and silt prevail. Autochthonous formation of some of the carbonates may be suggested from the fact that abundant Ca++ is supplied by affluents from the drainage area. Precipitation of calcium carbonate by means of changing physico-chemical conditions or photosynthetic activity of macro- and microphytes within the lakes is possible. 6.2. Analytical procedure Samples already split, for chemical analysis (see chapt. 7.2.), into fractions < 2 jum, 2—6.3, 6.3—20, and 20—63 pm were used for X-ray mineralogical determinations. Powdered samples were run with a Philips PW 1310 diffractome-ter at 36 kV and 24 mA. Nickel-filtered CuKa-radiation was applied. Total carbonate content was determined by the "bomb"-method (G. M u 11 e r & M. Gastner, 1971); a smaller type of "bomb" was used where only small amounts of the samples were left. Within the tables 10—14 some data are not complete; in this case no material was available since it was entirely used for chemical analysis. 6.3. Lake Bled Fifteen grab samples taken from the lake bottom, already split into upper and lower parts on board ship, and samples of two cores were analyzed. Upper and lower parts represent a top sediment layer of 0—3 cm (a) and a deeper layer of approximately 5—10 cm (b) below the bottom surface. Results out of a total of 58 samples 15 X 2 = 30 + 9 (= core BL-1B) + 19 (= core BL-15B) are discussed below (tables 10—12). In regard to both regional sample distribution (see maps fig. 12—13, figs. 1—4) and vertical penetration of the corer (fig. 9) the results must be regarded preliminary. 6.31. Grab samples Total carbonate content. The samples taken from the lake bottom have carbonate contents averaging about 70 °/o (54.5—78°/o range). Carbonate contents are different within different grain ?ize fractions. A general increase BLED Fig. 12. Lake Bled. Total carbonate content Above: Grab samples, upper part Below: Grab samples, lower part •j«z«r« / BLED Ž.p.Bl«d •iu«re BLED Fig. 13. Lake Bled. Dolomite within carbonate fraction Above: Grab samples, upper part Below: Grab samples, lower part CO o »o t o Z sot 60 •• -1-■—I-1 I-I— < 2/tm 3—6.3 6.3-20 20-63 > 63Jim % ® 100 ■ ■ cfl C O n s— CO 70 • ■ 60 - SO - 40 • 30 - 20 * -1— 2-e.3 6.3-20 20-ea^r of total carbonate with increasing grain size is observed from the < 2 fim fraction to the 6.3—20 /im fraction whereas it decreases significantly within the 20—63 fim fraction (fig. 14). Since clay mineral analysis from the <2/*m fraction failed to give definite results it must be assumed that most of the non-carbonate is probably biogenic material. This applies also to the other grain size fractions. Carbonate mineralogy. Most of the carbonate is low magnesium calcite but dolomite is also present throughout and is abundant within some of the samples; 2—38 of the carbonate fraction was found to consist of dolomite. An obvious difference of regional distribution of dolomite was found. Dolomite contents within the carbonate fraction are highest in grab samples 4, 5, 6, 7, 8, 12 and 13. A difference in dolomite contents was found between the upper and lower parts of the grab samples. Within the lower samples dolomite seems to reach a little further towards the central parts of the lake (fig. 13). This reflects that dolomite input had changed with time. Probably due to prior sedimentation, not much of the dolomite carried into the lake can reach its deepest, or central, parts. 6.32, Core samples The two cores BL-1B and BL-15B were separated into 9 and 19 samples, respectively. 6.321. Core BL-15B Carbonate content. Core BL-I5B has an average carbonate-content of about 67 %> (56.5—77% range). Carbonate contents within single samples are extremely variable. They are lowest within the < 2^m fraction ranging from 5.5—48.5 %. Again a general increase of total carbonate with increasing grain size is observed, with the exception of the 20—63 fim and coarser fractions (fig. 15). A rather good correspondence between the mineral composition of the finest studied fraction «0.063 mm) of the Solznik affluent (40 %> carbonate, see chapt. 3.4) and the uppermost sample of the core (57.5 % carbonate) reflects more or less the present conditions. Higher carbonate contents within all grain sizes are centered at 5—10 cm depth, reflecting that the sedimentation history of the lake had changed slightly with time. Carbonate mineralogy. Different amounts of calcite and dolomite were found from core BL-15B. Within most samples, dolomite contents are low (2—6 %> or slightly more) but some layers contain more than 10 •/» dolomite (12—18%). These higher dolomite contents are paralleled by higher amounts of quartz, thus they represent phases of detrital sedimentation. 6.322. Core BL-1B Carbonate content. Similar high carbonate contents as in core BL-15B were found from core BL-1B (total samples about 75 % average. Range is 60—79 •/»). Contrary to BL-15B the composition of the sediment is much more uniform as far as the total samples are regarded. The same pattern of carbonate content versus grain size is observed with highest contents within the 6.3—20 fxta fraction (fig. 16). The difference between sediment composition of both cores may have its origin in the position of core stations. Both cores were taken from similar water depths. Core BL-1B was taken from a central part with equilibrated conditions, whereas BL-15B is more marginal and most probably reflects the influence of the Solzni k affluent. Carbonate mineralogy. Calcite and dolomite are present but within total samples dolomite is rare (about 3 range 2—4 Vo). In the 20—63//m fraction, however, dolomite may reach up to 24 °/o (see table 11). This seems to be paralleled by the amounts of quartz although quartz-peak heights can reach similar maxima from samples of the < 2 fxm fraction without higher dolomite contents. Again, the dolomite seems likely to be of detrital origin. tf.33. Origin of the Lake Bled sediment Most of the sediments within Lake Bled are muds rich in, or entirely consisting of, carbonate material. Both calcite (low magnesium calcite) and dolomite occur. An approach to regional distribution of some parameters (carbonate content, dolomite content) must be regarded very tentative since sampling sites are scarce for such a purpose. Regional distribution of total carbonate content shows highest values in the central part of the lake, decreasing towards the northern shore. The lowest values occur within samples 12, 13 and 14 which can most probably be referred to the influx of non-carbonates from the Mišca affluent in the northwestern corner of the lake (fig. 12). In the mineral association calcite and dolomite prevail; there is considerably less quartz, and scarce feldspar (see tables 10—12). Most of this material is detrital but some calcite may also be autochthonous. Dolomite, however, is apparently detrital, as can be suggested from both regional distribution and linkage between dolomite and quartz contents of the samples (figs. 13, 17). Although quartz was only determined on a semiquantitative basis by X-ray diffraction, and peak height of the main peak was taken as an arbitrary measure, it is evident that within a similar matrix this gives reliable results. The regional distribution of dolomite within Lake Bled reflects transport from the north or from the northeastern and northwestern part of the lake surroundings (fig. 13). In the case of the northwestern bay, dolomite was apparently transported by the Mišca affluent; its sand- and gravel fraction was found to contain up to 70 %> dolomite (see chapt. 3.4). Contribution from the erosion of the shore rocks, however, is not evident. Likewise, the small island situated in the western part of the lake seems not to have much influence on nearby sedimentation: the adjacent sites 11 and 15 revealed comparatively little dolomite although this island consists of Triassic dolomite. Little can be said, so far, about the non-carbonates. Beside the scarce quartz and feldspar, abundant diatoms were found, particularly within the smaller grain size fractions. They are very well preserved. Selected samples investigated by scanning electron microscopy revealed several species of circular and elongated shapes which require further studies (figs. 18, 19). 6.3-20 20-63 63/tm quartz peak height Fig. 17. Total grab samples from Lake Bled Dolomite content of the carbonate fraction versus quartz peak height Figs. 18. and 19. Sediment from Lake Bled Diatoms from the carbonate free part of the < 2 /80% Fig. 21. Lake Bohinj. Total carbonate content Above: Grab samples, upper part Below: Grab samples, lower part Abundant opaline silica was already suggested from the typical "opal bulge' at the diffractograms of carbonate-free samples. The behaviour of clay minerals within the lake remains an open question. From the contribution of B. Ogorelec (see chapt. 3.4) it is evident that illite, chlorite, and smectite are transported by the small streams. Within the lake sediment, however, very little clay minerals could be determined. Although the hydrochloric acid method to remove carbonate was replaced by using cation exchange resin (R. M. Lloyd, 1954), clay mineral peaks remained poorly developed. A tentative suggestion may be that a break-down of clay mineral structures takes place due to dissolution of silica out of these clays. No data concerning silica concentration of the lake water are available so far but apparently silica concentration must be low in such lakes situated within an area consisting essentially of carbonate rocks. The abundance of diatoms, however, requires a source for silica, and clay minerals seem the most likely material to provide silica rather rapidly according to the results of F. T. Mackenzie et al. (1967). BOHINJSKO JEZERO fsm 51 - $o % MM 61-70% Fig. 22. Lake Bohinj. Dolomite within carbonate fraction Above: Grab samples, upper part Below: Grab samples, lower part 6.4. Lake Bohinj Eight grab samples were taken from Lake Bohinj and were split into upper and lower parts as the samples from Lake Bled. Additionally, one core was taken from the western central part of the lake; the core was split into 14 samples. A total of 30 samples thus represent the sediment of Lake Bohinj discussed here (tables 13, 14 and fig. 20). 6.41. Grab samples Carbonate content. The upper part of the grab samples have carbonate contents ranging from 53 to 91 percents. Most samples from the lower part have higher carbonate content than their upper counterparts. On a regional aspect, the present bottom surface sediment (if the upper parts of the samples really represent it) is different in carbonate content: the western part of the lake contains more carbonate than does the eastern part. This regional distribution is not valid, however, for the lower part of the surface samples, wherein high contents were found from both parts of the basin. Any suggestions about regional distribution, however, must be regarded tentative sofar because of the few sampling sites. Carbonate mineralogy. Both calcite and dolomite make up the carbonates of the lake sediment investigated. Little can be said — as was the case in Lake Bled — about their regional distribution. Figs. 21 and 22 represent tentative suggestions only. They also display the distribution within upper and lower parts of the samples. Again, a different input of sediment at different limes is evident. This also must be discussed with care, however, since not even the uppermost part of the samples really represents one sedimentation event. This holds true, much less, with the »lower parts* of samples which most probably are not time-equivalent in any case. No "single grain layers" were analyzed, but a mixture of layers representing different time span, instead. The ratio of calcite/dolomite is fairly uniform throughout all grain sizes. It is, on the average, about 50 :50 although a range of 70 %> calcite: 30«/» dolomite to 31% calcite: 69 % dolomite was found within total samples. With increasing grain size this ratio seems to shift in favour of dolomite; hence dolomite is, on the average, more abundant within the coarser grain size fractions. 6.42. Core BH-5B Carbonate content. The total samples range in carbonate contents from 65.5—76.5 °/o. Sofar, no phases of extremely different sedimentation events are obvious from the core. As within the grab samples of the lake the core samples also show carbonate contents increasing with increasing grain size (see fig. 23). Carbonate mineralogy. High dolomite contents, as already observed from the grab total samples, are also obvious from the cored sediment of this lake. On the average, both calcite and dolomite are present in similar amounts, although the ratio may reach from 69 °/o calcite : 31 % dolomite up to 5°/o calcite : 85 °/o dolomite within the carbonate fraction. From the present sampling sites a certain regional distribution of dolomite within Lake Bohinj seems to be evident. The upper part of the grab samples show higher amounts within the western part, reaching from sites 6 to 4 (fig. 3) which decrease — continuously? — towards lower dolomite contents at the eastern part of the basin. Both affluents Savica and Jereka could be responsible for the transport input of dolomite into the lake. According toB. Ogorelec (see chapt. 3.4) the Jereka sediment contains more dolomite than the Savica sediment and hence the Jereka is more likely the source of dolomite within Lake Bohinj. 6.43. Origin of the Lake Bohinj sediment Since the geological surroundings and the general sedimentological conditions of Lake Bohinj are partly similar to the neighbouring Lake Bled, a comparable origin of its sediments could be assumed. Accordingly the sediments are dominated by calcite and dolomite, quartz and feldspar being not common. In contrast to Lake Bled, however, no additional water is carried into Lake Bohinj which in Lake Bled could have influenced locally the chemical conditions of the lake water. A difference exists between both lakes as far as dolomite is concerned: The Bohinj sediment contains considerably higher amount of dolomite than sediment from Lake Bled. Although a relationship between dolomite and quartz contents is generally observed, the higher dolomite concentration of the Lake Bohinj sediment is not paralleled by correspondingly high amount of quartz. Dolomite seems to be derived from the lake's surroundings which consists of Triassic carbonate rocks. At the southern shore dolomite prevails whereas the other frame rock is slightly dolomitized limestone. Calcite is present throughout and is the dominant mineral phase within most of the sediments. The detrital origin of most of the calcite is beyond any doubt, but a small part may also be autochthonous. Evidence for calcite precipitation comes particularly from the southern nearshore sites 7 and 8 where the lake floor has a whitish appearance and ma* crophytes are abundant. Since the southern shore is composed of dolomite, the calcite within the nearshore sediment may have at least partly been precipitated by biogenic activity. As within Lake Bled, the non-carbonates include abundant opaline silica of very well preserved diatoms (figs. 24, 25). 6.5, Autochthonous formation and dissolution of calcite within Lakes Bled and Bohinj Although the sediments of both lakes clearly reflect a strongly detrital regime, formation of some autochthonous carbonate is indicated by our data. It is evident that high input of Ca++ into both lakes takes place since the affluence of both surface and ground water from an area consisting mostly of carbonate rocks is likely to contain high Ca-concentrations. Several mechanisms of CaC03-precipitation are known: Inorganic chemical precipitation may occur by either evaporation-concentration of the lake water or else by a mixing of water bodies of different composition. Biogenic carbonate precipitation due to the assimilation of plants is another possible mechanism. Evaporation-concentration is unlikely to explain an eventual carbonate precipitation from the lake water in Bled and Bohinj since the climatic conditions are not favorable. Mixing of different water bodies (e. g. the lake water and the Radovna river water) may eventually cause calcite precipitation although the water chemistry of both the river and the lake may not be very different. This model is unlikely, however, for the affluents. If, nevertheless, some carbonate precipitation occurs within such mixing areas, the small amount would be "masked" by the great amounts of detrital carbonate carried by the affluents. The main, if not exclusive, source of autochthonous calcite could then remain the biogenic activity of plants releasing CO2. Some of the nearshore environments, particularly at the southern shore of Lake Bohinj, have a whitish appearance, and underwater macrophytes are abundant there. Eutrophication effects, particularly within Lake Bled, are evident from several limnological data, and are also shown from the present study by U. Forstner (chapt. 7). The uppermost layer (0—3cm) contains up to 10.4°/o organic carbon (U. Forstner, 1977a in print) whereas the lower layer 9 — Geologija 21 -i— 2/.r 2-6.3 63-20 >63 Figs. 24. and 25. Sediment from Lake Bohinj. Diatoms from the carbonate-free part of the grain size 2—6.3 fim (5—10 cm) revealed only 2.2 %> (G. S c h m o 1 1, 1977). This high organic carbon content is referred to algal "blooms" which are known worldwide from many other lakes. Such algal "blooms" may be the most probable factor for autochthonous carbonate formation within Lake Bled and also Lake Bohinj. A certain increase of Ca within the < 2 jum fraction, though not always very pronounced, in the uppermost 10 cm of the sediment of the three cores studied (see table 16), may Carbonate in < 2 p < %) O 10 20 30 40 50 Interstitial water chemistry 10 20 mg/1 mmm mmmš mmmšT ■tZSiiXii mmk mm, mmm ■L ■h Fig. 26. Sediment core BL-15B from Lake Bled Chemical composition of the interstitial water indicate such biogenic precipitation of carbonate. Whereas the deeper layers of the lake sediments have a rather homogeneous appearance, the upper 5—10 cm of almost all samples show a distinct thin lamination (fig. 8), the top few centimeters consist of a textureless soft mud of a dark gray colour. The laminated part contains very thin white laminae of calcite. It is possible that this represents episodically precipitated autochthonous carbonate. Dissolved Ca++ is abundantly supplied to the lake water, although little data from the lake water for Ca++ were available (30—50mg/l; unpublished data of the Limnological station of Bled). The uppermost samples from the interstitial water (table 15), however are likely to present slightly higher values of Ca+ + than the lake water. They range from 100 to 170 ppm and are thus still double that of the lakes of Plitvice where carbonate precipitation takes place (P. Stoffers, 1975). From chemical analyses of the Lake Bled water at sites BL-1B and BL-15B (tables 1 and 2) it is apparent that already within deeper strata of the open water column carbonate can be dissolved rather than precipitated. A continuous decrease of pH-values from 8.5 and 8.4 at the surface towards 6.9 at 24 m and 26 m, respectively, is observed, and is paralleled by an increase of CO2, H*S and HCOs (I). Similarly, the temperatures decrease bottomwards, favouring carbonate dissolution. Chemical composition of the interstitial waters is also in favour of dissolution rather than precipitation of carbonate: An almost continuous increase of Ca++ and Mg++ is observed at core BL-15B which is independent of the carbonate content of the sediment (fig. 26). Sodium and potassium remain constant although some variations occur. Within the uppermost 10 cm of the core the decrease of carbonate can be explained by two factors which most probably act together: 1. The sediment is diluted by the high amount of organic matter (up to about 25%). 2. Decomposition of organic matter provides CO2 and thus causes dissolution of carbonate. A decrease of Ca within the uppermost layer is also evident from the other cores as is indicated by the results ofU. Forstner (chapt. 7). Dissolution of carbonate at similar depths (max. 22 m) was suggested from an extremely carbonate-rich part of Lake Constance ("Gnadensee", M. S c h 61 -tie, 1969), where about ten times more carbonate is autochthonous biogenic than detrital. 6.6. Sedimentation rates Without further dating comparison with other lakes of a similar setting, and the pollution effects within the uppermost centimeters of sediments can be used for dating purposes. Comparison with dated sediment cores from other lakes can only give approximate values. For the central part of Lake Constance an average of about 1 mm/a seems now reasonably established (G. M u 11 e r , 1966, *G. Wagner, 1972). In case of a similar sedimentation rate in both lakes Bled and Bohinj the lowermost samples within core BL-15B would not be much older than 400 years (see A. Sercelj and M. Culiberg, chapt. 5.2). Mass balance of the lake sediment is still an open question since almost no data are available for the input rate of suspended matter. The small affluents, as well as the artificial input of the Radovna water, seem to carry little suspended load (D. Vrhovšek & A. Brezigar, 1976). Input of further suspended matter was not measured since most of the detrital material seems to be transported by small torrents. Analysis immediately after rainfall is necessary. Probably, a large part of the detrital sediments may also be washed in by surface runoff similar to sheet-flows. From the few analyses of the chemical composition of the outflowing water of the Jezernica, it is evident, however, that suspended material is extremely scarce (about 10mg/l, unpublished data of the Limnological station of Bled). Since the affluents of these lakes are mostly torrents a rather discontinuous influx of detrital components must be assumed. Flood layers should be expected within the sediment column although they have not yet been detected within the uppermost 45 cm studied. 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'O • • o o N^NlONfr 0> — — — — O O ttnN-i-oonotrtciN ooomooioioioiooooio •o^fs-r-po'OooioNino-o Mrt A -o o o ee ifi n • ••i «•«*•• O O O O — .— CN CM CM _ — CM ^ I I If) rr - N O (N CM — — CN (T) CM CM CM OOOOOOOOiAOiOV) • I • O o n-ooN^NomoNce-ocoN — — — — OO — — CM— OOO^. N^'OnrjrsO'ON'flio^io mioifloiflioiooiooioooo «0 , _omoo.order to reduce the grain size effects as much as possible and compare the different samples, the grain size < 2 //m (pelitic fraction) was separated, in each case with distilled water in settling tubes. The suspended solids were recovered by evaporation in porcelain bowls at 60 °C. For the metal analyses, the dry material was treated with aqua regia (conc. HNOa : HC1 = 1:3). The elements lithium, sodium, potassium, magnesium, calcium, strontium, iron, manganese, zinc, chromium and copper were determined by conventional (flame-) atomic absorption spectroscopy and the elements nickel, lead and cadmium by means of flameless AAS according to the usual setting we use in this institute (U. Forstner & G. Muller, 1974). 7.3. Interpretation of metal data The analytical data of the elements investigated are registered in tables 16, 17 and 18. Mean values, standard deviations and variation coefficients for both areas of investigation are summarized in table 19. The distribution of the major and trace elements in the three core profiles are graphically presented in figure 27. 7.31. Mean values The comparison of the mean values (table 19) and variation coefficients of the metal data from the sediments of Lake Bled and Lake Bohinj indicates characteristic differences between both areas under consideration. There is a significant higher amount of calcium (30fl/o), lithium and potassium (50 °/o) and magnesium (100 %>), in the sediment of Lake Bohinj when compared with the pelitic fractions of the Bled sediment. Even stronger enrichment (150 to 300 «/o more than in Lake Bled) of iron, chromium, manganese and nickel has been found in the sediment of Lake Bohinj. The only significant exception with regard to the metals studied here, are the values of zinc, which are on the average, approximately 50 %> higher in the sediments from Lake Bled than in those taken from Lake Bohinj. Variation coefficients are relatively low for sodium, magnesium and calcium in both test areas, as well as for copper in Lake Bled and cadmium in Lake Bohinj; in contrast, the values of cadmium, nickel and lead from the sediments of Lake Bled indicate particularly strong variations, as the manganese concentrations likewise do in Lake Bohinj. With regard to the latter effect, it can be seen from the data of the grab samples that the top layers (0—3 cm) of Lake Bohinj are characteristically enriched in manganese as compared with the analytical values obtained from subsurface sediments (5—10 cm). From the present data of average values and variation coefficients of major and trace elements it would appear that there is a predominant lithogenic influence — from basic rocks — on the sediment composition of Lake Bohinj, whereas the elevated concentrations of zinc and the higher variability of the cadmium and lead values of Lake Bled point to anthropogenic influences. According to available knowledge (see chapt. 3.2.), however, basic source rocks have not been found in the catchment area of Lake Bohinj. The extremely high variation coefficient of manganese in Lake Bohinj is probably indicative of the presence of diagenetic effects that are brought about by changes in the redox conditions. The increase of manganese in near-surface sediments has been explained by processes of diagenetic dissolution of manganese compounds in the lower reducing part of the sedimentary column, upward migration of dissolved manganese ions and subsequent precipitation at the oxidizing sediment/water interface (E. Bonatti et al., 1971). These processes are considered important mechanisms in the formation of manganese concretions in the lacustrine environment (E. M. Kindle, 1932; R. Rossmann & E. Callender, 1968). Enrichment of manganese within the top surface sediment layers have been observed in Lake Constance (U. Forstner et al., 1974) and lakes of Upper Bavaria as well (U. Forstner, 1977b). 7.32. Core profiles The metal data from core profiles (fig. 27), which were taken from the eastern basin (BL-1B, water depth 24 m) and from the western basin (BL-15B, 29.6 m) of Lake Bled and from a water depth of 35 m of Lake Bohinj, confirm the findings described above. Within the upper part of the sedimentary sequence of the eastern basin of Lake Bled, we can note a distinct increase of the concentrations of zinc, lead and cadmium. Compared to the "background" data, presented by the respective metal values from the lower parts of the core profiles (approximately 150 ppm for zinc, 15 ppm for lead and 0.8 ppm for cadmium), there is a maximum enrichment in the surface sediment layers of the eastern part of Lake Bled by factors of 3.5 for zinc, 4 for cadmium and 10 for lead. In the western basin of Lake Bled, the surface enrichment is much lower for these metals, ranging between 2 for zinc and cadmium and 3 for lead. It seems quite probable from the core data that the enrichment of zinc, cadmium and lead in the surface sediments is due to the increased input of wastes from human activities. Similar effects can also be evaluated from the sediment core taken in the central part of Lake Bohinj. Significant enrichment in the surface sediment layers occurs: for copper, with concentrations up to 110 ppm (background 55 ppm) and zinc (420 ppm — 200 ppm). In contrast to the findings from Lake Bled, there is no characteristic increase of the cadmium concentrations within the upper portion of the core profile from Lake Bohinj. Decreasing values of chromium, nickel, and to a lesser extent, iron and potassium concentrations are found in the upper layers of the sediments in the middle of the lake; since there is a simultaneaous increase of the calcium concentration, we conclude that the depletion of Cr, Ni, Fe and K is due to the dilution effect by higher carbonate contents in the near-surface sediments. 8« «£3*5 >» W ® G gS c-2 g g m o -d v Ul «M ft) O* *•* /1 SI «1 flj ^ g O rt <■> e •P4 S 7.33. Inter-element relations Further insight into the factors influencing the distribution of major and trace metals could be expected from a statistical evaluation of the analytical data. Tables 20 and 21 indicate the correlation coefficients from linear regression analysis of possible element pairs for 28 samples from Lake Bohinj and 54 samples from Lake Bled. Values of more than 95 °/o significance are simply underlined; "r"-coefficients of > 99 %> significance show double underlining. Lake Bohinj. With respect to the last-mentioned effect of depletion of Cr, Ni, Fe and K and simultaneous increase of calcium concentrations in the core profile from Lake Bohinj, the calculation of the "r" coefficients seems to confirm our interpretation of carbonate dilution: there is a significant negative correlation between calcium on the one side and the metals lithium, potassium, iron, chromium, nickel and cadmium on the other. The latter elements form a first group of metals, which are positively interrelated, each to one other, with a probability > 95 %. Particularly high correspondence of the pairs K-Ni, Li-Fe, K-Cr and Li-Cr point to a common source of these metals from basic rocks; the presence of potassium and lithium in the strongly associated element pairs suggests that clay minerals might be the dominant carriers of elements, such as chromium, nickel, iron and cadmium into the sediment of Lake Bohinj. A second group of metals is formed by the elements zinc, copper and lead, which are correlated at more than 98 °/o significance. Although a common source of these elements from Zn-Pb-Cu mineralizations cannot be excluded, it seems more likely from their distinctly simultaneous enrichment in the upper part of the core profiles, that these three metals originate from increased anthropogenic inputs into the lake. Lake Bled. Significant dilution effects by carbonate components are restricted to the elements lithium, potassium and iron. The copper contents of pelitic sediments from Lake Bled are related both to the group of lithogenic elements, such as magnesium, iron, chromium and nickel, and surface-enriched elements such as cadmium, lead and zinc, which are positively interrelated with a particularly high degree of significance (> 99.9 Enrichment of the latter elements is considered to be predominantly induced by human-activities. Particularly heavy anthropogenic enrichment of Cd, Zn, Pb and Cu has been found by U. Forstner & G. Muller (1973) in sediment from the lower Rhine, by A. L. W. Kemp et al. (1976) from sedimentary core investigation in Lake Erie and byL. H&kanson (1977) from metal studies in the four largest Swedish lakes. This group of metals fully coincides with the frequency sequence of trace elements emitted in the atmosphere from burning fossil fuels (H. Erlenkeuser et al., 1974), which subsequently forms a characteristic "coal-residue-assemblage" in aquatic sediments (E. Suess, 1977). It has already been shown by H. H e 11 m a n n (1972) that elevated zinc and lead contents are indicators of increased input of sewage. After a review of lacustrine sediment studies from highly industrialized regions, it was suggested by U. Forstner (1976) that a moderate increase of the above-mentio-ned combination of heavy metals (Cd, Zn, Pb, Cu and Hg) is typical for mixed sewage inputs from urban sources. 7.4. Human effects on the metal composition of sediments from Lake Bled The distribution of the last-considered elements zinc, lead and cadmium in top layer samples from Lake Bled is shown in fig. 28. The dotted caption on the bottom part of each graph depicts the probable background values, as represented by the minimum metal contents in the deeper parts (15—25 cm) of the core profile BL-1B from the eastern basin of Lake Bled; dashed lines indicate metal concentrations of the subsurface samples from 5—10 cm depth and the solid lines show the actual levels of zinc, lead and cadmium in the pelitic fractions of the surface sediments of 0—3 cm. According to the present graph, a major source of enriched concentrations of zinc and lead must exist at the eastern shore of the lake. Typical increases of lead and zinc strongly point to the influence of sewage, which is most probably derived from the community of Bled. In contrast to that, the distribution patterns of cadmium values do not indicate a very distinct influence from the shore, and seem to be rather more affected by diffuse sources, such as characterized by atmospheric emissions. Another explanation for the distribution of cadmium could lie in the lithogenic influences from the north-western inflow to the lake, since the subsurface samples (5—10 cm) show a distinct decrease in cadmium between that point and the eastern shore. Finally, it cannot be excluded that soluble waste materials containing elevated cadmium concentrations are dispersed in the lake water and are partly coprecipitated with carbonate minerals. 7.5. Metal contents associated with the lake carbonate sediments Sediment analyses are not only useful when evaluating local sources of pollution and selecting critical sites for routine water sampling, they can also reveal the fate of contaminants under varying environmental conditions. In connection with the problems rising from the disposal of contaminated dredge material, methods of sediment partitioning have been developed. The most advanced techniques presently include the successive extraction of the metal contents in interstitial water and of ion exchangeable, easily reducible, organic and residual sediment fractions (e. g. R. E. E n g 1 e r et al., 1974). Here we are concerned mainly with the effects of carbonate associations of trace metals, since the sediments of both Lake Bled and Lake Bohinj predominantly consist of carbonate minerals. Table 22 gives the data of carbonate-associated metal contents from Lake Bled and — for comparison — of other lakes; examples from Central and Southeastern Europe, are analyzed after selective extraction, using strongly acid cation exchange resin (R. Deurer et al., 1978). By comparing the total carbonate percentage (in table 22 increasing from top to bottom) with the corresponding carbonate-associated metal content (given as percent from the total metal concentration), it is possible to deduce the effects of either enrichment or depletion caused by the carbonate component. If the metal content associated with carbonate is lower than the total carbonate, a dilution effect results, even when — as in the case of the result for iron — the metal content increases along with the carbonate percentage of the sample. It appears that the carbonate fraction is generally capable of bonding only up to 1/3 to 1/5 of the iron associated with the other sediment BLEJSKO JEZERO 500 i 11 10 1000m (JO —' r m o 2 3 4 5 6 7 8 St. 12 13 14 T T T T T T T T T TTTTT NNW - S SE -WSW - ENE 1000 Fig. 28. Concentrations of zinc, lead and cadmium in the clay-sized fractions of sediment samples from Lake Bled (top layer 0—3 cms and subsurface 5—10 cms) The dotted areas represent the geochemical background of the elements, as determined from the deeper layers of core IB Table 16. Metal data of peli tic sediment samples from core profiles of Lakes Bled and Bohinj BLEJSKO JEZERO - IB Li Na K Mg Ca Sr Fe Mn Zn Cr Ni Cu Pb Cd 0.5 _ 1.5 16 o. 24 0. 52 0. 49 9. 2 160 0. 74 140 4 BO 30 14 40 135 2. 08 1.5 _ 3 16 0. 22 0. .52 0. 56 7. 8 160 0. 74 90 510 36 14 40 117 2. 80 3 _ 5 16 0. 26 0. 42 0. 62 10. 6 160 0. .60 120 504 20 14 40 151 3. 24 5 _ 7 32 0. 44 0. 98 1. 14 16. 6 160 1. .08 190 280 38 24 40 60 1. 18 7 _ 10 24 o. 42 0. 66 0. 88 18. 8 160 0. .74 190 238 36 14 30 <58 1 . 09 10 _ 15 32 0. 30 0. 98 0. 84 9. 6 160. 0. .90 158 160 36 20 30 24 1. .09 15 _ 20 32 0. 26 0. 94 0. 69 6. 2 lOO 0. 90 100 180 58 22 30 14 o. 85 20 - 25 32 0. 24 0. 86 0. 65 5. .9 100 0. 90 100 192 40 22 30 20 0. 85 BLEJSKO JEZERO - 15B cm Li Na K Mg Ca Sr Fe Mn Zn Cr Ni Cu Pb Cd 0. _ 0.5 20 O. 76 0. .40 0. .71 18. .0 200 0. ,60 250 230 20 16 20 41 O. .73 0.5 _ 1 13 o. .43 1, ,44 1, ,68 16. .8 132 0. .53 158 216 21 16 21 37 1. ,05 1 _ 2 20 0. .51 0. .65 0, .86 16. .4 125 O. .63 150 248 25 19 20 37 1 . .18 2 _ 3 16 0. .44 o, .50 O. .89 16. ,6 160 0. .56 158 240 22 14 30 43 1 . .38 3 _ 4 13 O. .46 0, ,32 0, .74 18. .9 250 0. .38 163 330 20 8 38 45 t. ,14 4 _ 5 n 0. 40 0, .30 0. .77 20. .5 132 0. , 39 171 242 11 12 39 36 0. ,79 5 _ 6 20 0. .48 0, ,61 1. .02 18. ,2 160 0. ,67 216 350 22 20 40 32 0. ,93 6 _ 7 16 0. .46 0, .44 0, .84 19. .4 160 0, ,48 200 198 36 14 30 26 1. .00 7 _ 8 16 0. .46 o. .46 o, .84 19. .4 160 0. .43 224 322 30 26 30 28 1. .05 8 _ 9 20 0. .48 0, .66 0. .92 19. ,1 200 0. .60 240 336 30 16 40 30 1 . 10 9 _ 10 32 0. .54 1. .01 1 .08 18. .0 160 0 .90 240 380 36 20 40 30 1 .01 io _ 15 20 0. .46 0, .67 0. .88 17. .4 160 0. .80 200 220 30 20 30 23 1 .38 15 - 20 24 0. ,42 0. .82 0, .93 14. .6 160 0 .88 216 140 36 20 16 19 1 .00 20 _ 25 40 0. .41 1 .38 1 .02 8. .0 160 1 .40 200 164 40 26 30 21 0 .91 25 _ 30 36 0. .41 1 .36 1 .02 8. .8 160 1 .27 190 160 40 22 30 13 0 .73 30 - 35 44 0. .46 1 .67 1 .18 8. ,2 160 1 .58 200 140 40 32 30 17 0 .73 35 _ 40 44 0. ,46 1 .76 1. .20 8. .2 200 1 .58 190 144 22 35 40 15 0 .71 40 - 45 36 0. .42 1 .18 0 .96 9 .2 160 1 .05 140 262 22 22 30 13 0 .63 BOHINJSKO JEZERO - 5B cm Li Na ] K Mg Ca Sr Fe Mn Zn Cr Ni Cu Pb Cd 0 _ 1 42 0 .63 O .88 2 .17 16. .5 208 2 .24 750 383 92 57 67 112 1 .71 1 _ 2 50 0 .50 0 .80 2 .10 20 .0 250 2 .40 700 420 100 30 80 10!J 2 .30 2 _ 3.5 50 0 .46 1 .20 2 .32 16 .0 125 2 .45 540 345 90 70 100 112 1 .90 3,5 _ 5 40 0 .55 1 .26 2 .48 17 .3 166 2 .15 606 260 87 88 50 90 1 .47 5 _ 7 32 0 .52 1 .00 2 .04 21 .8 160 1 .92 496 160 76 62 30 61 1 .27 7 _ 8 32 0 .58 1 .00 1 .91 21 .8 160 1 .67 476 208 76 59 40 52 1 .34 8 - 10 36 0 .66 0 .95 2 .38 20 . 1 89 2 .11 589 321 71 68 54 75 1 .58 10 _ 15 42 0 .53 1 .23 2 .20 15 .7 132 2 co 573 263 105 80 21 78 2 .03 15 _ 20 43 0 .48 1 .32 1 .99 14 .5 174 3 .06 584 228 119 99 33 55 2 .22 20 - 25 40 0 .54 1 .32 2 .12 14 .6 100 2 .94 564 180 104 94 40 56 1 .94 25 - 30 44 0 .56 1 .47 2 .20 12 .2 100 3 .18 564 340 120 110 40 66 2 .27 30 _ 35 52 0 .50 1 .44 2 .38 12 .8 160 3 .12 552 224 104 120 30 54 2 . 16 35 - 40 44 0 .54 1 .41 2 .18 14 .8 160 2 .72 390 220 lOO 110 40 58 2 .05 40 45 40 0 .59 1 .38 2 .12 15 .6 160 2 .32 390 164 104 98 30 30 1 .41 Na, K, Mg, Ca and Fe in percent dry weight; Li, Sr, Mn, Zn, Cr, Ni, Cu, Pb, Cd in ppm Table 17. Metal data of surface (a: 0—3 cms) and subsurface (b: 5—10 cms). Sediment samples of pelitic fractions from Lake Bled BLEJSKO JEZERO Nr. Li ppm Na % K % Mg % Ca % Sr ppm Fe % Mn ppm Zn ppm Cr ppm Ni ppm Cu ppm Pb ppm Cd ppm la 25 0 .23 0 .36 O .60 8 .5 125 0.85 160 520 40 19 40 99 2.50 lb 20 0 .41 0 .76 1 .04 16 .4 160 0.88 224 408 36 25 40 62 1.34 2a 20 O .25 0 .53 0 .65 7 .1 50 0.80 158 560 30 25 40 104 3.53 2b 20 0 .41 0 .76 1 .07 16 .8 100 0.76 224 220 36 22 40 64 1.16 3a 20 0 .28 0 .36 0 .87 10 .5 125 0.62 175 600 20 17 50 86 3.04 3b 20 0 .42 0 .76 1 .07 17 .4 160 0.76 240 348 36 22 40 66 1.30 4a 17 0 .30 0 .43 0 .93 11 .8 266 0.72 200 516 27 13 50 82 2.13 4b 24 0 .46 0 .76 1 .14 18 .5 200 0.80 200 230 30 22 30 57 1 .00 5a 27 0 .37 o .63 1 .27 12 .5 266 1 .27 200 646 37 27 67 93 2.48 5b 40 0 .46 1 .50 1 .56 13 .4 160 1 .96 264 472 38 51 60 56 1.00 6a 20 0. .30 0 .69 1 .20 10.8 160 1.31 140 664 30 22 40 120 2.64 6b 64 0 .56 2 .20 1 .68 1 1 .0 160 3.06 660 230 90 108 60 64 0.86 7a 35 0. .56 O .58 1 . .85 15. ,8 250 1 .21 200 860 79 32 57 127 2.28 7b 25 0.46 0. .58 1. .55 22. ,5 400 0.68 190 310 50 10 40 65 1 .28 8 40 0. ,60 1. .05 1 . ,20 16. .0 400 1.68 225 970 75 36 75 160 2.03 9a 16 0. .29 o. .48 0. .65 9. .6 160 0.74 158 592 36 22 40 92 2.82 9b 20 0. .29 0. .59 o. .88 13. .6 160 0.76 224 416 36 20 40 81 1 .77 10a 20 0. .30 0. ,32 0.82 16. .7 200 O. 50 225 425 28 13 38 65 2.30 10b 20 0. 41 0. ,67 0. .99 17. .4 160 0.70 224 376 36 22 40 58 1 .49 1 la 13 0. 34 0. .35 0. 95 13. 7 200 0.56 163 388 25 13 38 53 2.70 lib 20 0. 43 0. .69 1 . 10 16. 6 160 O.76 180 416 36 21 60 54 1.85 12a 40 0'. 55 1. 20 1 . 68 15. 0 400 1 .25 250 450 55 26 75 58 1.15 13a 24 0. 33 0. 76 1 .04 9. 6 200 1 .40 158 400 36 26 40 86 2.80 1 3b 24 0.34 0. 78 1. 09 13. 4 160 1 .31 240 540 36 26 60 77 1.85 14a 20 0. 27 0. 76 O. 88 9. 0 160 1.08 158 464 38 24 40 80 2.32 14b 32 0. 38 0. 87 1 . 12 15. 1 160 0.90 224 388 40 28 40 50 1 .77 15a 24 0. 30 0. 86 1.07 8. 4 160 1.14 140 430 36 21 40 71 2.43 15b 24 0. 38 0. 83 1 .08 15. 1 160 0.94 200 320 39 24 40 53 1 .63 components. In the case of manganese concentrations, it was found that most of the investigated samples revealed an enrichment by carbonate. An exception was the sample from Lake Bled, where the relative low values of manganese might be explained in terms of diagenetic effects. The zinc values associated with carbonate seem to be relatively independent of the total carbonate percentage. Low values in lakes of high salinities can possibly be accounted for by the formation of soluble zinc-chloro-complexes, which influence the distribution coefficients of zinc during co-precipitation with calcite (K. H. Wede-p o h 1, 1972). In the samples from Lake Bled and Lake Ohrid (U. Forstner, Table 18. Metal data of surface (a: 0—3 cms) and subsurface (b: 5—10 cms) samples of pelitic fractions from Lake Bohinj BOHINJSKO JEZERO Nr. Li Na % K % Mg % Ca % Sr ppm Fe % Mn ppm Zn ppm Cr ppm Ni ppm Cu ppm Pb ppm Cd ppm 1 32 0.48 0.91 1 .76 16.8 100 1 .18 158 140 76 64 30 51 2.21 2a 2b 40 24 0.55 0.37 1.15 0.78 2.12 1 .08 16.9 16.8 167 200 2.56 0.84 1665 180 233 242 67 36 85 30 50 40 73 57 2.81 1 .54 3a 3b 50 20 0.50 0.33 1 .10 0.66 2.09 1.07 17.4 18.0 400 160 2.50 0.74 1090 224 340 208 90 22 83 24 40 80 94 49 1 .70 1.08 4a 4b 60 70 0.42 0.44 1 .64 2.16 1.61 1.56 9.0 5.7 160 100 6.10 4.52 2100 630 238 292 110 136 112 178 40 60 108 47 2.25 2.48 5a 5b 40 32 0.50 0.52 0.72 1.10 2.37 1 .84 19.2 22.8 125 160 2.25 1.68 950 476 450 156 55 68 61 68 75 30 100 38 2.45 1 .30 6a 6b 31 40 0.63 0.49 0.78 1 .07 2.40 2.09 21.2 20.3 193 167 1.93 2.18 1694 633 34 7 186 58 67 49 65 58 50 87 65 1 .66 1 .80 7 40 0.55 0.73 1 .90 21 .0 250 1 .58 166 280 55 66 40 49 2.15 8 25 0.53 0.74 1.46 23.5 200 1.00 125 275 45 36 20 33 1.63 1977b) concentrations of zinc correspond to the percentages of carbonate, i.e. neither dilution nor enrichment by carbonates takes place; in Lake Constance, the zinc contents are characteristically enriched through the carbonate sediment fraction, and partly by authigenic co-precipitation processes. The copper values reveal no systematic trend; the carbonate-associated copper percentages lie between 2%> (Lake Bled) and 10 °/o (Lake Constance), indicating that a dilution of copper is brought about, in all studied cases, by the presence of carbonate. Since chromium reveals no association with carbonate, it could be expected that the dilution effect should be even more pronounced that in the case of copper. , The chemical associations of heavy metals in sediments of Lake Bled have been listed in table 23 (from data of G. S c h m o 11, Heidelberg). It is evident that a large portion of the contents of nickel and chromium, and to a lesser degree of copper and iron are fixed in relatively inert positions to organic and inorganic detritus. The latter fractions are assumed to consist mainly of resistant heavy minerals, such as silicates and oxides. A considerable amount of nickel, chromium, copper and manganese is associated with hydrous oxides, although the major carrier, the hydrous oxides of iron, contributes only 0.02 °/a to the total sediment composition. As it has been shown from other examples of lake sediments (G. Schmoll, 1977), the oxyhydrate phases — either as direct precipitates or as co-precipitates with hydrous Fe/Mn oxides — effectively accumulate certain trace elements from the aquatic environment. Enrichment of metals in humic substances seems to be particularly important for iron and zinc; for the latter metal example the contribution from sewage effluents must be taken into account. Table 19. Mean valves, standard deviation and variation coefficients of the metal data from peiitic fractions of the samples from Lakes Bled and Bohinj BLEJSKO JEZERO (n«64) Mean Standard Variotion values deviation coefficient Li 25.1 -10 ppm 40 Na 0.40 ±0.11 % 28 K 0.77 i 0.39 % 51 Mg 0.99 i 0.29 % 29 Ca 13.75 14.34 % 32 Sr 177 1 67 ppm 37 Fe 0.94 i 0.61 % 48 Mn 196 t 76 ppm 39 Zn 371 t 178 ppm 48 Cr 35.9 ± 14.1 ppm 39 Ni 22.9 t 13.9 ppm 60 Cu 40.6 ± 13.7 ppm 34 Pb 60.5 ± 36.2 ppm 60 Cd 1.57 ± 0.81 ppm 51 BOHINJSKO JEZERO (n<8) Mean Standard Variation values deviotion coefficient Li 40.4 ± 10.5 ppm 26 Na 0.51 i 0.07 % 14 K 1.12 ♦ 0.33 % 30 Mg 2.01 i 0.37 % 18 Ca 17.22 ± 4.07 % 24 Sr 168 ± 61 ppm 37 Fe 2.38 i 1.08 % 45 Mn 635 ± 486 ppm 77 Zn 265 ±81 ppm 31 Cr 83.2 t 26.9 ppm 32 Ni 77.1 t 32.6 ppm 42 Cu 47.1 i 19.2 ppm 41 Pb 68.5 ±24.1 ppm 35 Cd 1.88 ± 0.42 ppm 23 Table 20. Correlation matrix for the metal contents in the pelitic fraction of sediments from Lake Bohinj BOHINJSKO JEZERO (n = 28) Li Na K Mg Ca Sr Fe Mn Zn Cr Ni Cu Pb Cd T 95 % probability; doubly underlined > 99 % probabilitiy Table 21. Correlation matrix for the metal contents in the pelitic fraction of sediments from Lake Bled BLEJSKO JEZERO (n = 54) Li Na K Mg Ca Sr Fe Mn Zn Cr Ni Cu Pb Cd Li X 0. 331 Q^glg -0.327 0.194 0..54 7 -0.094 Q^.667 0.768 0.251 -O.167 -0.358 Na 0.331 X 0.290 2==I11 Q-.604 0.209 0..4 95 -0.151 0.218 0.276 -0.019 -0.294 -0.502 K Qa.916 0.2 90 X -0.345 0.049 0^859 Qiill -0.277 0^488 QiZSl 0.147 -0.298 -0.402 Mg Qilil Qilll 0^548 X 0.212 Qilll Q^Iii 0.190 2illž 0^4 39 0.023 -0.124 Ca -0.327 QiiQi -0.345 0.212 X 0.324 ~Qi3£2 0.229 -0.085 -0.131 -0.208 -0.091 -0.158 -0.248 Sr 0.154 Qi426 0.049 Qilli 0.324 X 0. 148 0. 142 Qilil 0.354 -0.004 Qi462 0.248 0.039 Fe QiJiS 0.209 Qilll Q&yi -QMl 0.148 X QiSll 0. 110 Qilll QillZ QiiQi 0.093 -0.114 Mil Q M$ Qiin gtSil 0.229 0.142 0.617 X -0.068 Q-.818 0.235 -0.075 -0.239 Zn -0.094 -0.159 -0.277 0.190 -0.085 QsJI! 0.1 10 -0.068 X 0.304 0.035 Qi§80 Q^lii Cr QiifeZ 0.218 Q&593 -O.131 0.354 QiiQI 0. 304 X Qii^Z 0.280 -0.032 Ni Q^Zil 0.276 QiZH -0.208 -0.004 Q&§2 I Q^.818 0.035 Q^fiSi X 0. 331 0.030 -0.151 Cu 0. 251 -0.019 0.147 Qiill -0.091 QMl Qi.404 0.239 2&ŠI9 Q&547 0. 331 X SiiZl 0^367 Pb -0.167 -0.294 -0.298 0.023 -0.158 0.248 0.093 -0.075 Qiiii 0.280 0.030 Qž571 X Cd "Q^lli -g.|ga -Qi402 -0.124 -0.248 0.039 -0.114 -0.235 -0.032 -0.151 0^267 0^95 X Once underlined > 95 % probability; doubly underUned > 99 % probability Table 22. Carbonate-associated heavy metals in Lake Bled and other lakes: examples from Europe (Cc: calcite; MgC: high-magnesium cal-cite; Dol: dolomite). From R. Deurer et al. (1978) carbo- carbonate species Fe Mn Zn Cu Cr nate (%) in carbonate association percent (%) Cc MgC Dol of total metal phases Lake Constance 28 20 - 8 7 62 43 10 0 Neusiedler See 37 - 12 25 10 34 15 4 0 Lake Ohrid 44 44 - - 10 55 43 8 <1 Lake Balaton 55 - 41 14 20 68 13 5 0 Lake Bled 72 70 - 2 26 46 67 12 0 Table 23. Metal concentrations (Fe in other metals in ppm) and percentages of metal associations <*organic and inorganic residues + sulfides) in a sediment sample from the central part of the eastern basin of Lake Bled (data from G. S c h m o 11, 1977) Metal Total metal conc. Sorption + H20-*oluble conc. % Humic Substances conc. % Hydrous oxides conc. % Carbonate fraction cortc. % Residual fraction conc. % Fe 2.54 % 0.4 % 16 0.5 % 20 0.13 % 5 0.67 % 26 0.84 % 33 Mn 176 ppm 22 ppm 12 6,5 ppm 4 40 ppm 23 80 ppm 46 27 ppm 15 Zn 162 6.0 4 17.8 U 2 J_ 108 67 30 18 Cu 17.4 4.0 23 0.4 2 4.0 23 2.0 12 7.0 40 Cr 11.0 0.8 7 0.4 3 2.3 21 0 0 6.6 6? Ni 6.0 0.2 3 0.2 _3 2.0 33 0.2 _3 4.0 67 Composi Hon of the sample: 4.7 % org»subst« 0.02 % 72 % 23 % FeOOH carbonate residues 8. Summary and conclusions The sedimentological and environmental conditions of the Alpine border lakes of Bled and Bohinj presented here are part of a general program on Recent fluviatile and lacustrine sediments of Slovenia. This program was started in 1975, and problems of the Sava-river pollution and the Moste-dam have been studied since. This time a working group was engaged to sample the lake sediments and to examine them from the mineralogical and geochemical points of view. 15 grab samples and two core profiles (25—45 cm in depth) were taken from Lake Bled, and 8 grab samples and one core from Lake Bohinj. A brief geological and palynological survey of the surroundings of the lakes was carried out to delineate the origin of the sedimentary material and its pollen contents. The Bled sediment abounds in sewage and the lake water is characterized by dissolved plant nutrients and by the seasonal deficiency of oxygen in its hypo-limnion. Thereby it becomes eutrophic. To overcome this disturbance of the natural conditions a pipeline has been constructed to convey water of the Ra-dovna river into Lake Bled. Lake Bohinj, however, owes its biological equilibrium to a natural through-flowing stream. The results of the Lake Bohinj sediments are therefore particularly helpful as natural background data for pollution problems in Slovenia. Lake Bohinj should be noted, namely, for its rather high iron, manganese, chromium and nickel contents. Their origin has not been explained as yet. In the Lake Bled sediment calcareous silt and clay prevail associated with dolomite and organic admixture. The upper most 10 cms shows a laminated structure due to the alternation of inorganic and organic matter. Total carbonate contents of 56 samples are in the range of 55—79 %>, and are essentially the same in grab samples and core samples. Calcite prevails but dolomite may occasionally amount up to 38% of the carbonate fraction. The noncarbonates appear to be mostly diatoms, besides some quartz and traces of feldspar and clay minerals. Near surface sediments from all parts of Lake Bled exhibit an apparent odor from the decay of abundant waste matter from sewers. In the Lake Bohinj sediment total carbonate content ranges from 53 to 91 percent. Calcareous silt is indeed the prevalent constituent but dolomite content is higher compared to Lake Bled; it amounts locally to 69%. Dolomite is clearly detrital and is transported to the lake by its affluents whereas a small amount of the low magnesium calcite may also be autochthonous, particularly in the very shallow southern part. The non-carbonate sediments are essentially similar to the Lake Bled sediment, including also very well preserved diatoms. The content of organic substances within Lake Bohinj is much lower than within Lake Bled. Since both lakes are shallow (maximum depth about 40 m) and their surroundings consist essentially of Triassic carbonate rocks, most of the Recent carbonate sediments are supposed to be detrital. This is apparent for dolomite, but some calcite may also be autochthonous due to activity of plants. In general the Lake Bled sediment is more fine grained in comparison to that of Lake Bohinj. Clayey matter tends to prevail in it, while silt is more widespread in Lake Bohinj. Sedimentation rates appear to be higher in Lake Bohinj than in Lake Bled. The present study has revealed distinct human effects on the metal composition of the sediments from Lake Bled. A typical increase of lead, zinc and cadmium towards the youngermost layers strongly point to the influence of major inputs of sewage materials, which are most probably derived from the community of Bled. These effluents are considered to be responsible for the increased eutrophication during the last decades. Eutrophication seems to be delayed since fresh water is conveyed from Radovna river to the lake, although it is still continuing at a lower rate. With respect to these problems, further evidence should be gained from additional studies on the contents of nutrient elements, such as phosphorus, nitrogen, and organic carbon, as well as from the distribution patterns of contaminants other than heavy metals, e. g. synthetic organic substances. Further studies of the mineralogical and geochemical aspects of the lake sediments should be based on a more closely-knit net of grab samples and on sediment cores. The latter would be particularly useful to elucidate the geological history of both lakes, e. g. by pollen chronology. 9. Acknowledgements We are particularly indebted to the Research Council of Slovenia, Jesenice Iron and Steel Works, and Geological Survey Ljubljana for supporting this research project. The financial aid for metal analyses in the program "Geochemistry of Trace Substances in the Environment" was provided by the Deutsche Forschungsgemein-schaft We are obliged to the Boris Kidrič Chemical Institute Ljubljana for the aid given during the field work and the providing of presented limnological data, and to J. Podobnik for technical help and for the analyses of the lake waters. Thanks must be extended to A. Brezigar and to S. Zakrajšek for the assistance during the sediment sampling. The sieving analyses were carried out by Z. Germovšek, and the sedimentation analyses by V. Kogovšek. Grateful thanks are to Professor Dr. G. Muller from Heidelberg University for kindly provided laboratory facilities. The chemical analyses in chapter 7 of the lake sediments were conducted by I. Krtill from Heidelberg University. Data for the section on metal associations have been provided by R. Deurer and G. Schmoll. Chemical analyses of interstitial water were carried out by D. Reinhard. M. 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