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On the basis of generalization and analysis of long-term data, the peculiarities of the processes of pollution by nutrients of the waters of the Kuibyshev reservoir were studied and the specificity of the seasonal variability of nutrients was revealed. It was revealed that all the nutrients in the water of the Kuibyshev reservoir are characterized by seasonal variability, which is most pronounced in nitrate ions. The results of the study show that in 2009-2015 yrs perennial average monthly concentrations of nutrients did not exceed the fishery standards in the water of the Kuibyshev reservoir.

The results of the analysis of water pollution in the Kuibyshev reservoir with nutrients for the period 2009-2015 yrs are given. The assessment of the dynamics of average annual concentrations of biogenic substances and comparison with fisheries standards was carried out. The trends of average annual concentrations of biogenic substances in the water of the Kuibyshev reservoir are obtained, describing the general trend of the dynamics of biogenic substances for the studied period of time. The analysis of the changes in the chemical composition of the nutrient elements of the waters of the Kuibyshev reservoir in retrospective years from 1957 - 2015 yrs was carried out. In the modern period of 2009-2015 yrs marked a significant increase compared with 1952-1954 yrs the concentrations of the main biogenic substances - phosphate ions - 6,3 times, nitrite ions - 35,0 times, nitrate ions - 15,6 times, and ammonium ions 23,0 times.

Sustainable water use in a broad sense is a combination of all forms and uses of water resources that directly and indirectly affect the formation of the water fund. When operating hydropower facilities, it is necessary to comply with the requirements for the rational use and protection of water bodies. The article presents the results of the assessment of the specificity of water consumption and water disposal in the Kuibyshev reservoir within the Republic of Tajikistan, as well as the calculation and assessment of the main trends in water reservoir quality dynamics. Calculation of the index of the combinatory water pollution index during the period 2009-2017 yrs allowed to reveal a moderate tendency of its decrease within the limits of the 4th class of quality from the upper reaches to the dam of the Kuibyshev reservoir.