Spatial-Temporal Changes in Water Mineralization in Artificial Water Bodies of Kalmykia

The problem of changes, and especially deterioration of the quality of water in functioning reservoirs, is extremely relevant at the present time. In arid regions, the possibility of using reservoirs is limited by the increase in mineralization, but this issue has been practically unstudied and not covered in the scientific literature. The results presented in this article are original and for the first time characterize the features of quantitative changes in the spatial and seasonal transformation of water mineralization in reservoirs in arid regions over a long period of operation. The data were obtained as a result of long-term observations for the spring–autumn period from 2001 to 2023 at five reservoirs with different purposes and water regimes and located in the southern part of the steppe zone and in the northern part of the desert zone in the Republic of Kalmykia. In all reservoirs, the water mineralization was higher than the waters that feed them. In the Krasinskoye and Chograyskoye reservoirs, used for drinking water supply and filled with river waters from large rivers of other regions (Volga, Terek, and Kuma), the average value of water mineralization in the spring and autumn seasons was minimal (0.5 and 0.8 g/dm3; 1.6 and 2.0 g/dm3, respectively) in comparison with other reservoirs. The highest water mineralization was in the Tsagan-Nur and Deed-Khulsun reservoirs (5.8 and 32.0 g/dm3; 9.1 and 12.9 g/dm3, respectively), serving as reservoirs for the drainage and discharge waters of the Sarpinskaya and Chernozemelskaya irrigation and water supply systems. At the Arshan-Zelmen reservoir, created for irrigation and formed by the waters of local river runoff (2.9 g/dm3) and springs (0.4 g/dm3), the average mineralization value for the entire observation period was 5.3 and 19 g/dm3 in the spring and autumn seasons. It has been established that the mineralization of water in reservoirs with attracted runoff is not geographically determined. In reservoirs located in the desert zone (Krasinskoye and Deed-Khulsun), the mineralization value turned out to be lower than in reservoirs located in the steppe zone and having a similar purpose (Chograyskoye and Tsagan-Nur). The seasonal variability of the mineralization of water in all reservoirs is similar in that in the autumn period the values are higher than in the spring. Minimal changes were noted in drinking water reservoirs (Krasinskoye and Chograyskoye). The spatial variability of the difference in mineralization in different parts of the reservoirs is due to the fact that newly incoming waters have a lower mineralization than in the reservoir. The differences in water mineralization values between different sections of the same reservoir and between seasons are smaller than the lower mineralization value of its waters. At Krasinskii and Chograiskii, it does not exceed 0.3 g/dm3; on Tsagan-Nur, the reservoir with the highest mineralization, in the spring it is 7.9–8.7 g/dm3, and in autumn, 24.9–26.2 g/dm3. For drinking water supply and irrigation, based on the average long-term values of water mineralization, only water from the Krasinskii Reservoir can be used. Water from the Chograi reservoir, intended for drinking water supply and irrigation, based on the current mineralization value of about 2 g/dm3, can only be used for fishing and watering livestock of different categories.