Assessment of hydrochemical regime and production-destruction processes in the Kuibyshev reservoir during summer seasons with different weather conditions

The article presents the results of a study of the hydrochemical regime and characteristics of phytoplankton development in morphometrically different areas of the Kuibyshev Reservoir. Based on a number of hydrochemical and trophic indicators, a comparative analysis of the ecological state of the Kuibyshev reservoir was carried out during the summer periods of cold, low-water 2015 and hot, high-water 2016. It was shown that the formation of phytoplankton fields in the reservoir depends not so much on the water content of the year, but on the heating of the water column of the reservoir. In 2016, the values of Chl a, intensity of photosynthesis and concentration of organic matter averaged over the entire water area were 2-3.8 times higher than in 2015. During hot periods, the highest values of phytoplankton biomass, integral primary production and integral destruction can be traced in the lower and central areas of the reservoir, while the upper part is characterized by lower photosynthesis values. With an increase in water temperature, the average values of spatial heterogeneity coefficients (Cv) for almost all hydrochemical indicators in the Kuibyshev reservoir increase from 1.4-3.2 to 25-84%. The observation results show that in the summer season the daily production of plankton in the Kuibyshev Reservoir is twice as high as the daily supply of allochthonous organic matter with the waters of the total inflow. In the Kuibyshev Reservoir, which receives an influx of allochthonous matter, the intensity of destruction processes is higher than production processes, which indicates a good self-purifying ability of the Volga waters.