Features of the matter and energy flows in the plankton of deep northern reservoir with increased water color

Climate warming leads to changes in the temperature regime and irradiation in the northern lakes, in addition, to an increase in the water color, the content of organic substances, biogenic and trace elements in the water due to an increase in river runoff. In the Petrozavodskaya Bay of Lake Onego, winter river flow and water color have significantly increased over the past 20 years. In this work, using a mass-balance model, the flows of matter and energy in the plankton trophic network of this bay are calculated before the appearance of signs of brownification for further analysis of modern changes in the ecosystem functioning. The model was adjusted according to the empirical values of the specific phytoplankton and bacterioplankton growth rate, the regional dependence of chlorophyll a on phosphorus concentration in lakes was used. The results were controlled by empirical data on biomass and production of aquatic community. Calculations have shown the oligotrophic state and heterotrophic type of functioning of the Petrozavodskaya Bay ecosystem in the annual cycle in the 1990s. The plankton system receives an equal amount of autochthonous and allochthonous organic substances – 200 and 212.8 kcal/m2. Assimilation of organic matter by planktonic bacteria is 75% provided by allochthonous matter, and their biomass is two thirds. In the substance assimilated by grazer zooplankton, the bacterial component reaches 74%, phytoplankton – 26%. The biomass of grazer zooplankton consists equally of autochthonous and allochthonous substances. These features determine the low feed value of plankton for fish. Increased brownification with climate warming may lead to an increase in the contribution of allochthonous and a decrease in autochthonous organic matter to the biomass and production of bacteria and zooplankton, i.e. to a decrease in the bioproductivity of Petrozavodskaya Bay.