Species structure and diversity of phytoplankton of the Velikaya river delta (Pskov region, Russia)

The article considers the species structure and the temporal dynamics of some indicators of alpha and beta diversity of phytoplankton of the Velikaya River delta (Pskov region, Russia) in the summer period 2016-2017. Microalgae are important components of aquatic ecosystems because they form a significant part of a primary production. They are the first to respond to any changes in ecosystems, so, in addition to the coenotic, they have the most important monitoring value. The aim of the work was to study the species structure and some parameters of the diversity of phytoplankton in the Velikaya River delta at five specified stations. The Velikaya River delta is a unique natural complex, where the main riverbed divides into several branches, separated by low islands overgrown with macrophytes. Due to the peculiarities of the hydrological and climatic regimes, unique environmental conditions are created in the delta, which is reflected in the structure and species richness of the phytoplankton communities inhabiting it. In the course of the research, it was found that chlorophytic-diatomic complex of microalgae dominated in all sample stations during 2016-2017. When comparing the taxonomic composition of microalgae in 2016-2017 with the data of 1990-2000, a significant increase in the total species richness was revealed. It may be due to changes in the conditions of the delta ecosystem, as well as to the methodology for obtaining data. The average number and biomass of microalgae in 2016 were 1.6 million cells/l and 0.94 mg/l, respectively, and in 2017 - 460.1 thousand cells/l and 0.16 mg/l, respectively. Quantitative indicators of phytoplankton in 2016 were significantly higher than in 2017, due to temperature conditions and fluctuations in the water level in the delta. The values of the generalized alpha diversity indices in the separately considered phyla had significant differences. The obtained data indicate the presence of annual rearrangements in communities of microalgae, and they are more pronounced within individual phyla.