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environmental isotopes in the study of prespa lakes and underground connection between prespa and ohrid lakes

Introduction. Geographycal and geological characteristics of the Prespa

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environmental isotopes in the study of prespa lakes and underground connection between prespa and ohrid lakes

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    1. ENVIRONMENTAL ISOTOPES IN THE STUDY OF PRESPA LAKES AND UNDERGROUND CONNECTION BETWEEN PRESPA AND OHRID LAKES Jovan Zoto1, Ioannis Leontiadis2, Todor Anovski3, Lourence Gourcy4, Romeo Eftimi5   Institute of Nuclear Physics, Tirana, Albania National Research Center “Demokritos”, Athens, Greece University “Kiril i Metodij”, Skopje, FYR. of Makedonia International Atomic Energy Agency, Hydrology Section, Vienna, Austria ITA – Consult Company, Tirana, Albania     OHRID, May, 25–29, 2004

    3. Fig.1 Hydrogeological map of the Prespa–Ohrid Lakes system

    4. Mali i Thate mountain (in Albania territory) and Galitchica mountain (in FYR. of Makedonia territory) there are situated between three Lakes; they are composed, mainly by the carbonatic rocks and generally, are very karstified.   Some parts of the western lakeshore of Big Prespa Lake are very karstified; also, some parts of the eastern lakeshore of Ohrid Lake are very karstified, too.   St. Naumi and Tushemishti springs there are big karstic springs at the western part of the Galitchica and Mali i Thate mountains. Also, there are some small springs at the lakeshore of Ohrid Lake.   Based on the karstification of the mountains and the big altitudes difference of the Lakes system is formulated a hypothesis that big springs of St. Naumi and Tushemishti are recharged at least partially by Big Prespa Lake.   Some methods of the study are used for the confirmation of the hypothesis.

    5. Environmental isotopes method and its experimental data The environmental isotopes of Hydrogen and Oxygen at the water are used for the study of the Prespa Lakes and their underground communication with springs. The isotopic data are results of the study in frame of regional project of three countries (Albania, Greece, FYR. of Makedonia) and IAEA. The network of the measurements and sampling of water for isotopic analysis is in the Fig. 2. Measurements and sampling points : lakes; River; springs; Stations for precipitations.  Frequency and period of the investigation: generally, every two months during more than two hydrological cycles. The altitude effect of the isotopic composition of the meteoric water is used for the identification of the water coming from the different potential groundwaters.

    6. Fig.2

    7. Analysis of the Hydrogen and Oxygen stable isotopes were realized by the mass spectrometer. The analysis of Tritium were realized by the Liquid Scintilation Counting System. The values of Tritium are expressed in TU.   The stable isotopes of hydrogen are measured by hydrogen gas. The reduction reactions are : H2O + Zn ? ZnO + H2 2H2O + U ? UO2 + 2H2   Isotopic analysis of the oxygen were realized by the carbon dioxide (CO2), which is in isotopic equilibrium with the water samples. The isotopic exchange reaction is : C16O2 + H218O ? C16O18O + H216O The analytical equipment is a mass spectrometer with double inlet system and multi collectors system.

    8. For reasons of the measurement technique, it is determined the relative difference in the ratio of the heavy isotope to the more abundant light isotope of the sample with respect to a reference: d = Rsample - Rreference / Rreference where the Rsample are 2H / 1H or 18O / 16O.   The “d“ values of hydrogen and oxygen are expressed in per ‰ with respect to SMOW.   Refering the isotopic measurements of the water samples of the Prespa – Ohrid region and physical – chemical parameters it is created the Data Base of Prespa Lake and springs.

    9. Interpretation of the isotopic data and respective conclusions The Tritium values of the sampling points there are between 8.5 TU to 20.6 TU; Generally, there are in normal values.   The inflow sources of the Small Prespa Lake are the local sources, local precipitations and channel from Devolli River. The dynamic of the “d“ values (from – 8.9 and – 60.5 ? S.P. 2 to – 3.0 and – 28.9 ?S.P. 8) shows : a movement, relatively slowly, of the water at the Small Prespa Lake the evaporation process of the lake water The isotopic variation of d18O from the distance of the entry point of the Devolli River there is in Fig. 3 (linear line).

    10. Fig. 3 – Variation d18O = f (d )

    11. The inflow sources at the Big Prespa Lake are : Channel of Small Prespa, S.P.9; S.P-s 15, 16, 17, 18 Rivers; Local Precipitation. The dynamic of “d“ values of the Big Prespa Lake (from – 9.7 and – 62.5 at the East part of the Lake to - 1.0 and – 18.0 at the West part of the Lake) shows : a slowly movement of the water from East part to the West part of the lake; intensive process of the evaporation. the circulation time of the water in Big Prespa Lake seems to be very long. a very good mixing of the water Big Prespa Lake (“d“ values of Oxygen 18 of S.P. 10: -1.8, surf., -1.7, 11m, -1.7, 25m). The “d“ values of the big springs at the lakeshore of Ohrid (sampling points Nr. 23 – 25) there are very different from its corresponding values taking into the consideration of the altitude effect and continental effect. This means that, except the infiltration of the precipitations, an another watershed system has contributed at the discharge of the big springs; the rate of the evaporation of this watershed system, practically, is very high.

    12. The Prespa lakeshore at the its west part is very karstified and there seems visually the water inflow to the Mali Thate mountain, therefore the influence of the Prespa Lake to the springs is very important. Based on the isotopic data is calculated the contribution of the Prespa Lake to the springs No. 23 – 25 at the lakeshore of Ohrid Lake. By the calculation, 37.3% of the water of the St. Naumi spring (No. 23) has its origin from Prespa Lake and 54.4% of the water of the Tushemishti springs (No. 24 and No. 25) has its origin from Prespa Lake.   The relationship between d2H and d18O for the precipitation of the region Prespa – Ohrid Lakes there is : d2H = 8 x d18O + 13.8 The slope 8 of the LMWL is the same as Craig MWL but the deuterium excess 13.8 of LMWL is higher than respective excess of MWL. Nevertheless, deuterium excess there is in the interval of values for the Mediterranean zone. The variation d2H = f (d18O) is presented at the Fig. 4.

    14. Other sampling points, mainly, at the Small Prespa Lake, Big Prespa Lake, St. Naumi and Tushemishti springs there are at the line characterizeted by the equation : d2H = 5.176 x d18O - 13.286 where R2 = 0.9687 The slope of this line is lower than the slope of LMWL; it is attributed to waters with a significant rate of the evaporation. In this case, it is dedicated the intensive evaporation of Prespa Lake and, practically, the isotopic values of St. Naumi and Tushemishti springs represents values of “d“ of the mixing water in different proportions between precipitations and Prespa Lake water.   Relationship between d18O of the spring waters and the mean altitude of the corresponding recharge area (Mra), weighted by the surface area and the annual precipitation, for a wider area Prespa lake – Kastoria lake in Greece, is expressed : d18O = ( - 8.3 ± 0.15 ) - ( 0.001 ± 0.0001 ) * Mra, where R2 = 0.96168 This equation looks to be valid for the near area of the Albanian and FYR. of Makedonia territory. This is suggested by the d18O values of the water of the springs, sampling point Nr. 6, where d18O = (- 9.8 ± 0.1)‰, while the predicted one by the above equation is (– 9.7 ± 0.24)‰; the same may be true for the sampling point Nr. 20, where the actual d18O = - 10.5‰ value of the water of the spring, according to the above equation predicted value d18O = (- 10.3 ± 0.24 )‰.

    15. REFERENCES Anovski T.,Andonovski B., Minceva B. : Study of the hydrologic relationship between Ohrid and Prespa lakes, Proceedings of an IAEA International Symposium, IAEA-SM-319/62p , Vienna, 1991 Eftimi R., Zoto J. : Isotope study of the connection of Ohrid and Prespa lakes, International Symposium “Towards Integrated Conservation and Sustainable Development of Transboundary Macro and Micro Prespa Lakes”, Korcha, Albania, 1997. Environmental isotopes in the hydrological cycle (Principles and applications), Edited by W.G. Mook, UNESCO and IAEA, Paris 2000. Leontiadis I., Stamos A. : Isotopiki hydrologiki erevna evryteris periochis anu rou Aliakmona, 5th panhellenic hydrogeological symposium, Limasol, Cyprus (greek with English abstract), 1999. Stable Isotope Hydrology, Deuterium and Oxygen-18 in the Water Cycle, Technical Reports No. 210, IAEA, Vienna, 1981.

    16. Thank you for your attention

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