ИСТИНА

The chemical composition of water in lake Gusinoe, situated in the Selenga river basin was studied in summer 2019. The factors, which probably influence the lake ecosystem during summer period: discharge from Gusinoozerskaya thermal power plant, municipal wastewater discharges, and drainage water from closed coal pits in southern part of the lake’s watershed were considered. The water quality research was based on the data from the network of 19 monitoring stations. The concentrations of major ions, trace elements, and nutrient elements (P, Si) were analyzed in 56 samples of water, suspended and bottom sediments. An extensive impact of human activities is observed in the vicinity of the city of Gusinoozersk, where high concentrations of Sr and increased content of Zn, Cu, Mo were found. There is no significant influence on the water chemical composition of closed coal mines in the southern part of the lake. Concentrations of nutrient elements are high in the northern part of the lake, due to the sewage discharges from Gusinoozersk and runoff of the Zagustay River. The nutrients and warm water, which comes from the thermal power plant, cause the growth of planktonic organisms, but the central and southern parts of the lake can be considered as oligotrophic. In summer, the chemical composition of the lake's waters in most cases is weakly affected by anthropogenic factors. However, uncontrolled discharge of sewage may pose a threat to the hydro-ecological state of the lake in future.