Phytoplankton as an Indicator of Ecological State of the Neva River Estuary for 2011–2015

During the study period, the general pattern of distribution, species composition, and abundance of phytoplankton differed from those recorded previously. The greatest changes are observed in the central part of the northern coast of Neva Bay. As previously, the phytoplankton biomass is about 1 mg L−1 in the Neva Bay near eastern station 7 on the northern coast, while it is 2–3 times higher than the previously observed biomass near station 12. On the whole, the phytoplankton biomass in this area is 6.1 ± 2.9 mg L−1 in 2011–2015, which corresponds to the eutrophic level of productivity. The phytoplankton biomass of 15.8 mg L−1, which was recorded in late July 2015 and was dominated by algae Chlorophyta, characterizes this area of the Neva Bay as highly eutrophic. Against the background of currently observed processes of eutrophication in the Neva Bay and the eastern part of the Gulf of Finland, the summer phytoplankton (late July–early August) is dominated by different groups of algae. The mean biomass is 6–7 mg L−1 in the most productive area of the internal estuary (station 19). Periods of cyanobacterial water blooming at a biomass of over 22 mg L−1 are also most often recorded here.