Isotopic Methods for Studying Issyk-Kul Lake
Studying Water Balance and Hydrodynamics of Lake Issyk-Kul with a Help of Isotope Methods
Tech Area / Field
- OBS-GEO/Geology/Other Basic Sciences
- OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
- OBS-OTH/Other/Other Basic Sciences
8 Project completed
Senior Project Manager
Kulikov G G
Institute of Water Problem & Hydropower Engineering, Kyrgyzstan, Bishkek
- VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- Pirkanmaa Regional Environment Centre, Finland, Tampere\nURA 0073/Universite Paris-Sud, France, Orsay\nInternational Bureau for Environmental Studies, Belgium, Tervuren\nUniversità di Roma "La Sapienza", Italy, Rome
Project summaryThe goal of the project is studying water balance, hydrological budget of Issyk-Kul basin and hydrodynamics of lake Issyk-Kul with a help of isotope methods.
The choosing of the object of study depends, on the one hand on unique climatic and geo-hydrological conditions, and, on the other hand, on their typicalness for Central Asian region. Closed pluvial high mountain lakes are the most sensitive for regional and global climate changes. The latter allows to consider the Issyk-Kul basin as a natural model, in which various water processes are presented within a comparatively small area (22,080 km2). Studying these processes with a help of isotope methods it is possible to extend and elaborate not only our knowledge in hydrodynamics of the Issyk-Kul, a mechanism of circulation of natural waters over the region, but it adds some to a model of global circulation of water.
The isotope methods were chosen because they give an opportunity to extend and amplify the results obtained by traditional methods of geo-hydrology. It is proposed to apply tritium- and uranium isotope methods for dating waters of different types, as well as when building a model of moving moisture and calculations of the balance. Use of stable isotopes of hydrogen and oxygen will make it possible to estimate a part of local moisture in balance of studied basins and find out the rate of circulation of moisture.
Topicality of matters proposed to study in the project is determined by the process of global warming and regional (Central Asian) desertification. In view of this, amplifying water balance of lake Issyk-kul will help to implement obtained results to planning effective use of water resources, and preserving ecological balance.
In previous years within the studied region various researches had been carried out in field of geohydrology, that is why the proposed studies allow to amplify the results obtained before.
The fourth in depth over the world (Hmax= 668) lake Issyk-Kul is of interest to the scientists for many years. Issyk-Kul has a great value for the economy of Kyrgyzstan. However, many problems of this unique object have no solutions up to now. One of them is a stable lake-level’s decline, that is 13 meters since the fifties of last century and 3.2 meters from 1927 to 1996 according to observations data. To solve this problem and the others, it is necessary: to study with a help of isotope methods a water balance and hydrodynamics of lake Issyk-Kul.
It is expedicient to use natural radioactive(3H, 14C, 234U/238U) and stable (16O/18O) isotopes when studying processes of water exchange in close lakes, which Issyk-Kul is, since in such reservoirs during evaporation the specific isotope composition of lake waters is formed. It differs from isotope contents of feeding sources-atmospheric precipitation and river discharge. One can judge by difference in isotope contents about influence of the lake on nature of moisture circulation in the basin.
One of the questions being of interest both scientifically and practically is a question on a role of ground sources in water balance of the lake Issyk-Kul (Vikulina, 1946; Tsigelnaya, 1960; Kaplinsky, Timchenko 1977; Shnitnikov, 1977, 1979; Zektser, Diordiev, 1979, Gronskaya, 1983; Krivoshey, Gronskaya, 1986). More than 50% of the river’s discharge has being taken for irrigation, when going to lakeside plaint. At the same time, a portion of taken water evaporates from the fields irrigated and goes outside the hollow, and some portion go away from rivers beds from the lake itself. One can understand an influence of irrigation when knowing that while 118 rivers are in the hollow, only 30 of them feed the lakes during whole the year. It has been marked the tendency for many years of reducing expenses of water in summer and of increasing them in winter. In the mouth of the river Ak-Terek (West) a maximal discharge is marked in winter time of the lowest water (February) at the expenses of coming return waters.
Use of uranium and tritium as natural radioactive isotopes seemed to be prospective when studying losses of the river discharge related with taking water for irrigation. Application of this method for solving mentioned problem is based on considered processes of forming river discharge a result of mixing surface waters (precipitation, melted waters from glaciers and snows) with ground waters of zone of active water exchange of hydro-geologic massif. If waters from different sources are rather c contrasting then the part of different components of the discharge could be determined in isotope composition U234/U238 and total contents of uranium on the base of equation of isotope dilution (Chalov, Tuzova, Merculova, 1983).
Tritium is a good indicator when studying natural waters because of similarity its physical and physically-chemical properties with hydrogen, and radioactivity (the transformation period 12.26 years) makes it possible to obtain temporal characteristics of migrating water in different parts of hydrosphere.
When accomplishing work on studying the influence of taking water for irrigation on losses of river discharge it is necessary to take samples of water from rivers in their mouths and in out to lakeside plain, as well as from filtrometers installed in zone of wedging ground waters on the bottom of the lake Issyk-kul. The experiments with filtermeters carried out by the Institute of Water Problems in 1986 have shown anomaly high concentrations of tritium amounting to 240 TU under normal value in the lake 9-18 TU (Meskhetely, Bergelson, 1989). For installing filtermeters ping suits are used.
Comparing isotope compound of hydrogen, oxygen, uranium in all types of waters of Issyk-Kul hollow, i.e. atmospheric precipitation, surficial and ground flows, in the lake itself it has being planned to calculate a ground inflow, that is the hardest to determine.
Adopted isotope methods will give an opportunity to estimate a part of local moisture in hollow atmospheric precipitation and a part of moisture evaporating from Issyk-Kul water area and fields of irrigation, gone outside the hollow. As the Issyk-Kul hollow is surrounded by high mountain ranges, the streams carrying moisture percolate in it through lowering relief on the west and leave it through lowering relief on the east. According to present-day ideas, the local moisture part in precipitation of Issyk-Kul hollow amounts to 50% (Brezgunov, Romanov 1989).
To amplify these data it is necessary to take samples of water and then analyse the atmospheric precipitation, that includes determinating concentrations of tritium, deuterium and isotopes of oxygen, hydrogen and uranium in lake waters. For analysis of isotope composition of waters in the Issyk-Kul hollow the Kreig’ and Dansgaard’ diagrams are applied, which have been widely adopted in isotope studies for hydrology.
The Issyk-Kul hollow can be considered a unique model of nature with the most of normalities in of disseminating stable and radioactive isotopes typical for the global circulation of natural waters because of existing seat of intensive evaporation in considerably isolated Issyk-Kul hollow in form of non-freezing lake, the areas of condensing moisture in form of atmospheric precipitation and glaciers as well as river flows which transport the moisture into the lake.
Tritium and isotope composition of oxygen could also be used as tracers when studying processes of water exchange in lake Issyk-Kul itself. When stratosphere is a source of tritium, and troposphere moisture and surface water of hollow are, at the same time, the transporting agents, then the lake itself is a discharge reservoir of for most quantity of tritium.
Issyk-Kul is a monomixing lake which has a vertical water exchange once a year in winter under the water temperature higher than the temperature of maximum density. The depth of vertical water-exchange in Issyk-Kul is determined by winter temperature. In warm winters, when the vertical density stratification of water mass take place, the partial water exchange to depth 200-300 m. goes on, while in cold winters the total vertical water exchange to maximum depth 668 m occurs. The studying of distributed tritium in cross section of lake carried out in summer 1978 and winter 1979 (Brezgunov, Nechaev, Romanov, Romanovsky, 1980) showed a high concentration of tritium in upper layers of lake in summer and in zone of maximum depth in winter.
Now the vertical water exchange in lake Issyk-Kul occurs twice in 3 years (Romanovsky,1991). But the climate warming marked since 1973 in Tyan-Shan can create in nearest future such situation, when the vertical water exchange will cover only an upper sector of water. That threatens to form sulphohydrogen zone in deep layers of the lake (Mamatkanov, Dikikh, Romanovsky, Shambetov, 1997).
So, studying dynamics of water masses of the lake Issyk-Kul lake is an actual problem of the Issyk-Kul environment. All the works including taking of water samples in surface and deep waters in August (the period of maximum stratification), in November (the period of active convective mixing), in February (the period of homotermy), in May (the period of active mixing wind) should be carried out for two years.
Creating mathematical model of large-scale mixing water in lake Issyk-Kul requires to account to estimate the importance of the whole complex of phenomena and factors.
Mathematical base of these processes is composed by problems of hydrodynamics of convective vortical streams.
The experimental data of hydrobalance, thermal flows, density and other parameters side by side with isotope data will be used for descibing mixing of water in the lake.
On the basis of adaptation and development of available physico-mathematical models and software the model will be created of large-scale mixing water in lake Issyk-Kul.
Calculations will be carried out in the framework of spatially two- and three-dimension discrete models taking into account geometry of lake bed.
Isotope, hydrodynamic and hydrological parameters obtained after completion of proposed project will be used to test correctness of the model and then forecast development of water processes.
So, using isotope methods gives an opportunity to accomplish reconstruction of climate of Tien Shan in early Pleistocene and Holocene, to reveal to what extent lake Issyk-Kul influences on structure of local precipitation, to determine direction of taking out and quantity of atmospheric moisture gone outside the hollow, to determine the volume of ground waters discharging to the lake, to construct a model of large scale mixing water in lake Issyk-Kul.
In practical terms, benefit of accomplishing model of balance and hydrology is in opportunity of efficient forecasting the sequences of different ways of disseminating water resources and their impact on ecological system of Issyk-Kul basin. Models of different sequences allow to choose optimal ways of ecological and economic activities and make appropriate management decisions in different climatic situations.
Hydrological model of lake Issyk-Kul makes it possible to carry out analysis of hydro-chemical, hydro-physical and hydro-biological data. On the ground of this analysis it is possible to plan activity on increasing biological productivity of the lake, to prevent it from recreational and industrial pollution.