Zooplankton Community of Lake Lebyazh’e (Kazan, Russia) under Changing Conditions
The paper presents the results of long-term observations (1991-2015) of zooplankton community in Lake Lebyazh’e (Kazan, Russia). Lake Lebyazh’e is a system of four water bodies: Bol’shoe, Maloe, Svetloe, and Sukhoe Lebyazh’e lakes, all interconnected with channels. Under the influence of anthropogenic and natural factors, a decrease of the water level and shrinkage of Lake Lebyazh’e took place. In order to save the valuable recreational facility, a range of hydrotechnical measures have been carried out. To date, the lake area has decreased by about 13 times; the water level is maintained artificially by supplying groundwater, which caused an increase in water mineralization, prevalence of sulfate ions. This, in turn, has led to changes in the structure of zooplankton community. The values of species composition have reduced significantly (by more than 20%). According to the recently obtained data, zooplankton of Lake Lebyazh’e comprises 44 species: 26 rotifer species (59%), 14 cladoceran species (32%), 4 copepod species (9%). New species, which were previously uncommon in the lake, have been found. It has been revealed that the range of dominant species of zooplankton changed, and their abundance decreased. The quantitative values of zooplankton decreased. It has been demonstrated that the abundance and biomass of zooplankton prior to the exposure corresponded to mesotrophic-eutrophic water bodies, but today’s quantitative characteristics of zooplankton are more of oligotrophic water bodies. Based on Shannon’s index, the species diversity of zooplankton has not decreased. However, most species are represented by either single or low number of individuals. This suggests that all organisms forming the community of Lake Lebyazh’e have evenly become less abundant. According to the saprobity index, the lake is β-mesosaprobic, moderately polluted, and corresponds to class III of water quality. It has been concluded that the characteristics of zooplankton can be used as indicators to describe changes in the ecosystem initiated by variations in hydrological conditions, salinity, and main ions.