Response of Phytoplankton of the Kiev Reservoir to the Increase in Summer Temperatures

Abstract

It has been found that in 2011-2016 global and local climatic changes in the ecosystem of the Kiev Reservoir manifested themselves in excessive summer temperatures of the water: in the surface layers of water - to 27.2-28.8°C, whereas in its near-bottom layers - to 25.9-26.6°C. The response of phytoplankton to excessive temperatures manifested itself in changes in its taxonomic diversity, abundance, structural organization, and in the processes of production and decomposition. At the present time, Chlorophyta, Bacillariophyta, and Cyanoprokaryota are highly diverse in their species composition. However, small-sized Chrysophyta and Cryptophyta also contribute significantly to the total number of phytoplankton species (8 and 5 species and 17 and 8%, respectively). Previously they occurred only in early spring. On the whole, two types of algal communities differing in their species composition, abundance, and structure are formed depending on water temperature. A direct relationship was established between the excessive temperature of water registered in summertime and the intensity of Cyanoprokaryota and Chlorophyta development. At the same time, the intensity of Bacillariophyta development depended inversely on summer temperature. The maximal values of the total, net primary production, and organic matter decomposition significantly differed from their minimal values. On the whole, the excessive summer temperatures of the water did not result in the irreversible changes in the structural and functional organization of phytoplankton belonging to the main component of the autotrophic chain of the ecosystem of the Kiev Reservoir.