ВЛИЯНИЕ СОЛЕНОСТИ ВОДЫ НА РАЗВИТИЕ ПРИДОННОЙ ГИПОКСИИ И УРОВЕНЬ ПЕРВИЧНОГО ПРОДУЦИРОВАНИЯ ОРГАНИЧЕСКОГО ВЕЩЕСТВА В ТАГАНРОГСКОМ ЗАЛИВЕ

Abstract

At present, the Azov Sea ecosystem exists in the context of continuously decreasing continental runoff and increasing water salinity, which reached in 2020-2021 the highest values for the entire period of observations since 1962. The increase in water salinity inevitably leads to the transformation in the composition of biological communities, which has a pronounced effect on the environment and fisheries. This paper discusses the long-term impact of water salinity on the development of near-bottom hypoxic phenomena and on the volume of primary production of organic matter by phytoplankton in the Taganrog Bay during the summer season (1962-2021). A statistical ecosystem analysis describing the contribution of the major hydrological and hydrochemical factors into the processes of hypoxia formation in the bottom water layer of the Taganrog Bay has been performed. It is shown that the desalinization of the waters of the Taganrog Bay in 1993-2008 was accompanied by the increase in the size of hypoxic zones in the bottom water layer. During the modern period of salinization extending from 2009 to the present, there has been recorded a decrease in the scale of oxygen deficiency in the Taganrog Bay. The most crucial contribution to the hypoxic processes in the Taganrog Bay is provided by the stability of water masses, water temperature, organic nitrogen concentration, and the water salinity (due to the effect of salinity on the stability of water masses). During the streaks of the Taganrog Bay salinization, the decrease in the stability of water masses and in the content of organic nitrogen and phosphorus in the water (crucial factors in the formation of hypoxic zones) has been recorded. The highest rates of the primary production of organic matter by phytoplankton in the Taganrog Bay were observed during the desalinization period of 1962-1968, and the lowest ones were recorded during the salinization periods. The results of this assessment have exposed the significant relationship: the primary production of organic matter depends on the average annual runoff of the Don River, the water salinity, and the concentration of mineral nitrogen.