Seasonal dynamics of phyto- and zooplankton and their relationships in a small urbanized reservoir, by the example of the Lake Bolshoe Vasilievskoe (Togliatti city, Samara region, Russia)

The abiotic environmental factors and the composition of phyto- and zooplankton were homogeneous along the entire water body in a shallow polymictic hypereutrophic urbanized Lake Bolshoe Vasilievskoe (Togliatti city, Samara region, Russia). The species composition of phytoplankton was quite diverse and corresponded to the type characteristic of small water bodies of the middle and lower reaches of the Volga River. Zooplankton was represented quite poorly, mostly by eurybiont species, which were the indicators of a high degree of organic pollution. During theyear, the species composition of the entire phytoplankton and the complex of dominant forms of algae corresponded to a certain stage of the seasonal periodicity and successive change of hydro-climatic phases for shallow hypertrophic water bodies. We analyzed the communities of phyto- and zooplankton and their relationships under the influence of eutrophication and seasonal changes in abiotic environmental factors. Summer cycles of phyto- and zooplankton abundance and biomass dynamics had opposite dynamics. In autumn, there was a synchronous decrease in both abundance and biomass of phyto- and zooplankton, associated with the natural seasonal cycles of abiotic environmental factors. In winter, the abundance of warm-water zooplankton species was higher than that of typical cold-water species; the opposite patter was observed in summer. The method of the correlation pleiades of Terentyev revealed that phytoplankton was the main environment-forming component of the ecosystem in the Lake Bolshoe Vasilievskoe. It was also found that an increase in the level of trophicity of the Lake Bolshoe Vasilievskoe, including an increase in the concentration of biogenic elements (nitrogen, phosphorus), affected the zooplankton community through phytoplankton community indirectly.