INTRA-ANNUAL VARIABILITY OF PLANKTON COMMUNITIES IN THE ESTUARY REGION OF THE SEVERNAYA DVINA RIVER

The paper summarizes the results of monthly studies of phyto- and zooplankton communities of the estuarine region of the Northern Dvina, conducted during environmental monitoring from November 2020 to January 2022 at the water intakes of JSC “Arkhangelsk Pulp and Paper Mill” (Novodvinsk) and LLC “RVC-Arkhangelsk” (Arkhangelsk and Silikatchikov settlement). Based on the results of plankton surveys, the qualitative composition was studied and the intra-annual variability of quantitative indicators and structural features of plankton communities was described. In phytoplankton, 273 intraspecific taxa of microalgae were found, among which diatoms predominated (159 taxa). The indicators of abundance and biomass changed synchronously during the entire observation period. Primary production and P/B coefficients were at the level of digital values for the Arctic zone. The Shannon Index identified the phytoplankton community as medium-complex in a stable state. 45 species belonging to 4 systematic groups were found in zooplankton. Seasonal dynamics of zooplankton was characterized by 2 peaks of abundance and biomass – in November 2020 and July 2021. By species composition, the zooplankton community in the water intake areas in February–June 2021 it can be characterized as a kladocern, in July – as a rotifer-kladocern-copepod, in August as a rotifer-kladocern, and December can be considered the end of the growing season. The degree of contamination was assessed according to the index of saprobity of phytoplankton and zooplankton. It was found that the state of the waters of the Severnaya Dvina River in the study area corresponded to the oligo-β-mesosaprobic zone or class II water quality (moderately polluted).