Content of Nutrients in the Lakes of the Onon-Torey Depression during the Period of Climatic Fluctuations

Using the example of brackish and saline lakes in South-Eastern Transbaikalia, the influence of low-water and high-water years on the ecological status of steppe lakes is considered. Cyclic fluctuations in climatic conditions at intervals of 27-35 years cause consistent filling and drying of lakes. The abiotic conditions associated with climatic fluctuations, as well as the intensity of the biochemical and biological processes taking place in the ecosystem, the level of organic matter introduced from the catchment area, determine the dynamics of nitrogen and phosphorus concentrations in the aquatic environment. On the basis of generally accepted hydrochemical methods, the change in the content of nitrogen and phosphorus, organic substances in the ecosystem of a number of lakes of the Onon-Torey basin (Bain-Tsagan, Tsagan-Nor, Yaksha, Naryn-Bulak, Ara-Torum, Batuy, Bain-Bulak, Balyktui, Ukshinda) was investigated and residual lakes of the Barun-Torey lake basin) in order to clarify the state of the lakes during the transitional period of low-water and high-water years. An assessment of the dynamics of physicochemical parameters revealed that climatic conditions (aridization or humidification) determined mineralization. In dry years (1983-86, 2018), the processes of evaporative concentration of salts became essential. In this regard, the mineralization is almost doubled and reaches up to 7 g /l. The interannual dynamics of nitrogen and phosphorus was characterized by a large amplitude of concentration fluctuations. A low content of total phosphorus in 1983, 1986 (low-water period) increases by 2011, with a decline by 2018. A large amplitude of fluctuations of the parameters studied is associated with the level of accumulation of organic matter in the bottom sediments of lakes of organic matter in low-water years. In the high-water years, the investigated lakes were of fishery importance. In 2018, due to a decrease in the water surface area and an increase in water salinity, the fish fauna was not found in these lakes. Conducted research is necessary for planning water use of lakes.