Plankton communities of lake Okhta-Nyarvi (Northwestern Karelia)

Inventory of the current state of phyto- and zooplankton communities of Lake Okhtanyarvi was carried out for the first time. The lake, thanks to its geographical location, is a part of the Green Belt of Fennoscandia. Species diversity, the ratio of the main taxonomic groups, the structure of the dominant hydrobiont species, their abundance and biomass in the littoral and pelagic zones of the lake have been studied. The results of the research showed that according to the level of phytoplankton quantitative development in the summer of 2013, the waters of Lake Okhtanyarvi can be attributed to the third class of quality, category 3a (“sufficiently clean”), which corresponds to the ß-mesosaprobic zone by the scale of saprobity. The average value of the saprobity index, calculated from the quantitative ratio of indicator zooplankton species, makes it possible to attribute the lake to the oligosaprobic class (second class of quality, pure natural waters). Lake Okhtanyarvi can be considered a convenient control water body for monitoring the state of the environment in the border areas.