Retrospective analysis of phytoplankton community structure in water bodies of South Ural (Russia)

Abstract

The current paper considers changes of phytoplankton community structure in three South Ural (Russia) water bodies different in trophicity: Lake Uvildy, Lake Ilmenskoe, and Shershnevskoe Reservoir. There is no clear relation between the changes of species structure of phytoplankton communities and water-bodies trophicity. The least significant changes in the phytoplankton community structure are registered for the mesoeutrophic Lake Ilmenskoe, which is located on the territory of the State Reserve. Diatomic, green and blue-green algae groups are the most diverse in composition in the studied periods of 1936-1937, 1964-1984 and 1998-2016. But for the last 20 years, Cyanophyta has increased its contribution into the phytoplankton number and biomass of Lake Ilmenskoe. The representatives of the Bacillariophyta group dominate in oligotrophic Lake Uvildy. In 1965-1985, the Chlorophyta group was the most abundant in Shershnevskoe reservoir (34 % of the total number of species), Bacillariophyta -32 % and Cyanophyta – 18 %. In 2003-2005 and 2017 the number of green algae increased (Chlorophyta – 40 %) and that of diatoms decreased (Bacillariophyta -21%) with the number of blue-green algae being unchanged (Cyanophyta -19 %). The ecological status of the Shershenevskoe Reservoir has transformed from a long-term sustainable mesotrophic to eutrophic. So, for oligotrophic lake Uvildy and mesoeutrophic lake Ilmenskoe, Bacillariophyta group is characterized by the greatest taxonomic diversity. While for eutrophic Shershnevskoe Reservoir the absolute abundance of Chlorophyta algae group is marked, which is growing in time. The growing importance of blue-green algae is one more feature of the change of a trophic status.