Production characteristics of phytoplankton of the Vygozerskoe reservoir (Karelia) under the conditions of reoligotrophization of the ecosystem

The article presents the results of a study of the phytoplankton production characteristics of the Vygozerskoe reservoir in August 2017 after a 26-year decrease in nutrient load. Photosynthesis is reliably related to water temperature, chlorophyll a, phytoplankton abundance, and the share of green and blue-green algae, Euglenophyta in the community. The values of photosynthesis, the concentration of chlorophyll a and total phosphorus did not exceed the values of 20072011, when reoligotrophization was already taking place. These parameters in 20072011 and in 2017 corresponded to the natural state of the ecosystem in the early 1970s. Values of chlorophyll a in 20072011 and in 2017 remained higher than in the early 1970s. A high share of indicator species of increasing trophic level remains in phytoplankton. We can say that the reoligotrophization of the ecosystem is completed. The persistence of phytoplankton changes may result from an increase in the degree-days of the biological summer because of climate warming in the region.