Isotopic Study of Karst Water
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Jr-> n <'-' FKPOPT KO. IABA-R-2845-F TITLE Isotopic study of Karst water PIKAL RKPOPT FOR THE-'PERIOD I98I-O4-OI - 1984-05-31 AUTHOR(S) H. Leskovsek-Sefman INSTITUTE Institute "Jozef Stefan" Ljubljana Yugoslavia INTEPKATIONAL ATOMIC EMFFGY ACEKCY DATE January 1985 FINAL REPORT ON RESEARCH CONTRACT No. 2845/fcB ISOTOPIC STUDY OF KARST WATER J. Pezdic, H. Leskovsek-Sefman, T. Dolenec, J. Urbane April 1981 to December 1983 Ljubljana, 1984 univerza e. kardelja institut "jo2ef Stefan" Ijubljana, jugoslavija univerza o kardeljj institut"jo2ef Stefan" Ijubljanajugoslavija FINAL REPORT ON RESEARCH CONTRACT No. 2845/RB ISOTOPlC STUDY OF KARST WATER I J. Pezdic, H. Leskovsek-Sefman, T. Dolenec, J. Urbane I J.Stefan Institute, University E. Kardelj, Ljubljana, Yugoslavia I April 1981 to December 1983 1 1 I 1 I 1 i Ljubljana, 1984 I I CONTENTS INTRODUCTION GEOLOGICAL AND CLIMATIC CHARACTERISTICS 4 Precipitation 4 PLANINA CAVE 8 Streamlet 1 10 I Streamlet 6 and Tihi rov 16 1 CAVE CARBONATES 21 UUBLJANICA RIVER BASIN 27 I THE WATER CATCHMENT AREA OF Rlf ANA 32 i THE WATER CATCHMENT AREA OF IDRIJCA 38 CONCLUSIONS 42 i REFERENCES 46 I I 1 I I I Final Report on Research Contract No. 2845/RB - July, 1984 I ISOTOPIC STUDY OF KARST WATER I J. Pezdic, H. Leskovsek-Sefman, T. Dolenec, J. Urbane I J. Stefan Institute, University E. Kardelj, Ljubljana, Yugoslavia I Summary I Mass spectrometric investigations of the isotopic composition of some elements in water and in dissolved carbonates from the Slovenian Karst are presented. Additionally, the isotopic composition of oxygen and I carbon in cave carbonates is given. The results allow the conclusion that the waters in karst aquifers do homogenize to a great extent, but qualitative determination of the I retention time and of the prevailing sources for some springs and water flows is nevertheless possible. I The isotopic composition of O in water and of O and C in dissolved carbonates depends on climatic conditions and on denudation processes. So a fairly good estimation of paleoclimatic conditions from the isotopic I composition of cave carbonates also becomes possible. I INTRODUCTION Measurement of the isotopic composition of water formed part of an I extended investigation of the water drainage system in the Slovenian Karst. These studies were planned to complement geological and speleological investi- I gations (i.e. regular determination of water flows, temperatures, contents of dissolved substances, as well as water tracing with fluorescent dyes) which are I already being performed in this area, with a knowledge of the mechanism of changes in the isotopic composition of water in the natural environment on some smaller (model) locations. As such a location Planina cave near Posrojna, was chosen where we studied the vertical percolation of meteoric water through the karstified carbonate ceiling, and the water catchment areas of some small rivers in the Slovenian Karst, such as the river basin of the Ljubljanica, and - 2 - the water catchment areas of the rivers Rizana and Idrijca. In the karst, where water percolation is relatively rapid, changes in the isotopic composition of water owing to rainfall can be significant. I Because of lithological characteristics, differences in porosity of the minerals which are fissured and cracked in many different ways, owing to specificities in I the karstification process, and last but not least, because of different vegetation, the water retention in several parts of the aquifer varies a great deal, and so I characteristic homogenization of the meteoric waters takes place. All the above mentioned influences vary from place to place and as a rule the isotopic compo- 1 sition of the rainfall varies too, so in spite of the homogenization process, the aquifers contain water of different isotopic composition. This enables the tracing I of the predominant sources for various springs and flows at accessible places. In dissolved carbonates, the isotopic compositions of oxygen and carbon were I measured. The oxygen composition is related to that of water by the equilibrium isotopic ratio of oxygen, which shows a temperature dependence. The second parameter - the isotopic composition of carbon - is important, because this element 13 can be incorporated into the dissolved carbonate from CO9 in air (6 C = 13 1 - 7 %o), from CO9 of organic origin (8 C= - 25 %o), or as dissolved carbon- 13 ate from sea carbonates (6 C = - O to + 3 %o), the latter prevailing in +he 13 I area under investigation. The great differences in the 6 C values enable a I relatively exact determination of various components. I - 3 - I I I I I I / \ jlum VIi I I I I I «•winrti/n?"1" * /' I T mtUorolojic «tallan I M = I: 500.000 " o «tmpllni pdnt I Fig. I: The map of the investigated area I 1 n - 4 - GEOLOGICAL AND CLIMATIC CHARACTERISTICS The area where the investigations of karst waters took place lies in the SW of Slovenia. From the geotectonic point of view, it belongs to the northern part of the Dinaric Alps. The landscape is rather mon tai nous, there are many I karstified mountain chains and high plateaus, with scattered karst poljes and I flysch reefs (Fig. 1). Mountains and high plateaus reach a height of 'about 1300 m above sea level; I Snetnik even 1796 m. The Karst poljes are to be found especially along the Ljubljanica river basin. The flysch reefs have the direction of the Dinaric Alps', I which means NW-SE. Surface flows are to be found only on karst poljes and on flysch, while water flows in the karstified limestone area are underground. I Slovenia belongs to a transitional climatic region between the continental and the Mediferranion climates. Just in the Ljubljanica river basin is this transition I most evident - because of the so-called "Postojnska vrata". In the cooler half of the year, the Dinaric high plateaus are a barrier high enough to divide Slovenia into its inner (continental) part with severe winters and its SW (littoral) Primorje, where the mild winters show the influence of the Adriatic Sea. Preci pi tati on The isotopic composition of precipitation was followed during the entire period of our investigations. The main sampling place was the meteorological station in Ljubljana, which provides basic data for other hydrogeological investigations in Slovenia. All the hydrometeorological data for longer periods are collected together there. So we were able to obtain the average precipitation, air temperature and average humidity in Ljubljana for the last 20 years. The avera- ge rainfall was 1402 mm, the average temperature 9.8 C and the average humidity 7.7 mb. Data for single months and years throughout the period of our investigations are presented in the following table (Table 1), together with - 18 - - 5 - UUBUANA, YUGOSLAVIA Lat. 46°04' Long. 14°31' Alt. 299 msl Maan 1956-80, Prac. 1402 mm. Mun 1956-80, w.P. 10.21 mb, Mein 1956-80, Ttmp. Yt«r Month Prtcip. S18O SO T Tamp. Mean vJ*. mm Ko Ko T.U. 0C milli barr 1981 May 147 - 8.15 - 64.7 70 14.3 112 Juna 171 - 9.39 - 64.0 83 182 15.0 July 94 - 7.19 - 47.6 64 19.6 16.1 Augutt 129 - 6.30 - 30.0 65 183 16J) Stpttmbff 214 - 7.33 - 46.3 26 16.1 13.7 • Octobiir 140 - 7.66 - 54J) 18 12.1 12.7 Nova mt>«f 30 . -11.69 - 86.7 16 3J) 72 I Daoambar 216 - 7JtO - 49.7 15 0.0 4.3 18 Yur Month Pracip. O O SD T Maan tamp. Mun V.P, 0 I mm Ko Ko T.U. C milli barr 1962 Januar 64JO -8.83 - 63.4 40 - IJ) 4.4 Fabruar 18,6 -14.44 -106.0 — - 0.7 A3 March 84.9 - 9.70 - 70.3 19 4.9 6.9 I April 262 -8.33 - 552 32 8.4 7.0 May 199.1 - 7.62 - 54.6 25 14.9 11.7 Juna 2634 - 6.63 - 47.0 31 19.0 15J3 1 July 43J) - 5.11 - 34.7 61 212 17.9 August 1582 - 721 - 49.1 32 19.9 16J) Scptambar 86J) - 5.47 - 31.0 24 17.9 17.0 October 234.6 -8.43 - 57.1 20 11.1 11.6 Novambar 102.0 -13.22 -101.9 14 • 5.9 8.4 Decembar 146.9 -14.33 -113.2 17 3.7 7.0 Sums 1418.0 Maani + 10J 10.6 Wt. muni - 8.66 - 62.3 26.1 8 Yfar Month Pracip. o' O SD T Maan tamp. MHn VP. 0 mm Xo Ko T.U. C milli barr 1983 Januir 36.3 - 9.68 - 68.8 27.6 1.3 6.5 Februar 110.6 -14.06 -104.2 16.2 1.1 4J3 March 147 A -11.63 - 87.6 23.6 6.1 6.9 April 48.9 - 6.43 - 42.7 202 12J) 92 May 168.0 -8.45 - 60J 22.9 152 12.0 Juna 94.6 - 7.51 - 49Ji 36.4 18.4 14.3 July 313 - 4.17 - 22J3 61.6 22.6 17J) August 117.4 - 535 - 34.0 32.9 19.7 16Ji Saptambar 91.7 - 7.69 - 62.7 20J) 16.6 13.7 Octobar 127.5 - 9.81 - 70.1 202 10.0 OJB Novambtr 30.7 - 6.19 - 402 11.7 1.7 5.9 Dacamb«r 145.4 -10.00 - 71.7 30.7 0.4 6.1 Sumi 11492 Maans 102 10.1 Wt. maans - 9.06 - 64.3 24.4 TABLE 1: Avaraga monihly precipitation in Ljubljana from 1981 to 1983.