The State and Dynamics of Biological Communities in the Rybinsk Reservoir under Climate Changes

Abstract

The long-term data on structural characteristics of phytoplankton (1954-2014) and zooplankton (2004-2013), as well as chlorophyll content in the water and bottom sediments (2009-2014) in the Rybinsk Reservoir (Upper Volga, Russia) were analyzed. It was shown that the modern climate changes lead to transformation in the state and dynamics of biological communities that is characteristic of the trophicity increase. After the abnormally hot summer of 2010 a sharp rise in chlorophyll content in water with a predominance of values typical for eutrophic and highly eutrophic conditions was detected. Distribution of plant pigments in the bottom sediments was similar in different years, which shows the specific character of the sediment complex structure in the reservoir. In the seasonal dynamics of phytoplankton biomass and chlorophyll concentration the summer maximum caused by development of cyanobacteria began to dominate above the spring one. In the structure of phytoplankton the proportions of cyanobacteria and myxotrophic phytophagellates increased, the invasion of brackish-water diatoms was marked, and diminution of the cell size was noted. In seasonal dynamics of zooplankton biomass the second late peak was formed in August and it was particularly pronounced in the abnormally hot summer of 2010. In addition, there was a 1-2 week shift in timing of the beginning and ending in seasonal cycle of a number of zooplankton species relative to the 1960-1970s. Appearance of a summer dissolved oxygen deficiency (up to 1-4 mg O 2 /L in the layer of

Changes in the structure and dominance of the zooplankton community of the Kremenchuk Reservoir under the effect of climate changes

“…The main responses of freshwater zooplankton to climatic influences are considered to be changes in the abundance, distribution and structure of zooplankton communities (Vadadi-Fulop et al, 2012). Changes in zooplankton abundances in response to rising average temperatures were shown for some reservoirs and lakes (Jeziorski et al, 2016;Korneva et al, 2019); however, in other lentic systems, the dynamics of zooplankton abundances in the context of climate change did not show clear trends (Carter & Schindler, 2012;Fomina & Syarki, 2018). In this regard, there is a question about the impact of these changes on the structural and functional parameters of main groups of aquatic organisms as a component of the study of patterns of transformation of aquatic ecosystems in conditions of regulated river flow and multi-vector impact of external factors (Romanenko et al, 2019).…”