Phytoplankton, bacterioplankton and detritus of Verkhnevolzhsky reservoir and unregulated part of the Upper Volga in 2011

The results of the analysis of phyto- and bacterioplankton and detritus of the Upper Volga area (Tver region) during the spring tide and the summer low-water in 2011are presented. Quantitative characteristics of studied components varied within the following limits: phytoplankton 0,06-13,7 10 6 cells/L and 54-1695 mg/m 3; picophytoplankton 5,6-380 10 6 cells/L and 3,8-34,2 mg/m 3; bacterioplankton 0,7-3,6 million cells/mL, and 18-113 mg/m 3; picodetrit 0,02-1,03 10 6 part./mL and 10.8 -1097 mg/m 3; nanodetrit 0,01-0,49 10 6 part./mL and 71-17997 mg/m 3. Abundance and biomass of phytoplankton and bacterioplankton in the studied area increased during the transition from the spring tide to the summer low-water, and the number and mass of detritus decreased. Diatoms were the dominating group of phytoplankton, especially in the mouths of tributaries. Picocyanobacteria were its constant, although minor component. Pico- and nanodetrit played an essential role in ecosystems of studied area, possibly as the main source of food for the zooplankton. Based on the combination of abiotic and biotic factors, stations were divided into three groups with distinct differences in the composition of seston.