The Content of Dissolved Oxygen in the Water of the Kuibyshev Reservoir Under Conditions of Mass Development of Algae

Abstract

The aim is to quantify and establish the causes of seasonal variability in the content of dissolved oxygen in the conditions of mass development of algae in the Kuibyshev reservoir. Materials and methods. In the period 2001-2020, systematic observations were carried out at a stationary point in the outlet section of the Kuibyshev reservoir. The spatial heterogeneity of the degree of saturation of the surface layer of water with oxygen was estimated according to the data of periodic observations from the vessel "Biolog" equipped with the information-measuring water quality system "Khiton". The observation program was developed taking into account the weekly and daily regime of regulation of the water line in the alignment of the Zhiguli hydroelectric complex. Results and discussion. It has been established that the seasonal variability consists of four periods, which differ in the multidirectional formation of the oxygen regime, and includes two minima in the content of dissolved oxygen. The winter minimum was observed in March at the end of freeze-up, and the summer minimum was observed in August during the mass development of algae. One of the reasons for the formation of the summer oxygen minimum is the process of mass development of blue-green algae, due to which a thin surface layer of water supersaturated with oxygen is formed. This layer of water hinders the flow of oxygen from the atmosphere into the water in a significant part of the water area of the reservoir. In the abnormally hot summer of 2010, the surface oversaturated with oxygen accounted for more than 30 % of the reservoir area, which contributed to a decrease in the oxygen content in the water mass to critical concentrations. Findings. Under the conditions of growing biogenic load and global climate warming, the intensity and duration of the process of mass development of blue-green algae in the Kuibyshev reservoir will only increase, which will lead to a deterioration in water quality and the emergence of water use risks.