Influence of weather conditions on the dynamics of summer phytoplankton in the Kuibyshev reservoir

Abstract

Based on observation data in the summer of 2019 and 2021, an assessment was made of changes in abiotic characteristics and chlorophyll (Chl) content in the Kuibyshev Reservoir. Regular observations were carried out at the outlet section of the reservoir (Zhigulevsky hydroelectric complex) under conditions of complete mixing of water masses. The main goal of the study is to assess the influence of abiotic factors on the chlorophyll content and the mass development of cyanobacteria. It has been established that the main influencing factors are thermal regime and weather conditions. 2019 is characterized as “cold”. The total number of days with water temperatures above 22 °C was only 11. The degree of favorability was low (23 °C ˃ t ˃ 22 °C). 2021 characterized as “warm”. The total number of days with water temperatures above 22 °C was 72. The degree of favorability varied widely: from low (23 °C ˃ t ˃ 22 °C) to extreme high (t ˃ 26 °C). The most favorable year for the mass development of cyanobacteria was 2021, when the Chl content over the summer period was 7.2 μg/dm3. The least favorable year was 2019, when the Chl content was 1.4 μg/dm3. Seasonally, the temperature optimum was observed annually in July. The Chl content in July 2021 was 12.6 μg/dm3, and in July 2019 – 1.8 μg/dm3. Significant variability in chlorophyll content is due to synoptic cyclicity and changing weather conditions. The established influence of thermal regime and weather conditions on the content of chlorophyll suggests that in conditions of global warming, the process of mass development of cyanobacteria is expected to intensify, which will negatively affect the ecological state and water quality of the Kuibyshev Reservoir.