The model of substances redistribution in the waters of Petrozavodsk bay of Onega lake

Climate changes on the territory of Karelia have led to an increase in the intake of allochthonous substances in water bodies. Over the past thirty years, the removal of dissolved and suspended humus substances, as well as iron and phosphorus in their composition, from the waters of the Shuya River to the Petrozavodsk Bay of Lake Onega has been growing. The brownification processes led to lower water quality and negatively impact on benthic communities. To estimate the volume of intake, removal and deposition of allochthonous substances that entered Lake Onega with the waters of the Shuya River, simulation modeling was applied. A number of model variants were constructed including data on three substances (iron, phosphorus, suspended substances) and a year-round cycle of water dynamics. The model parameters were the coefficients of transport and “disappearance" (sedimentation) of substances from the waters of the Petrozavodsk Bay. The parameters were adjusted based on field data on the chemical composition of river and lake waters for 1992-2018. The model calculates the concentrations of substances that are compatible to real data, and also makes it possible to estimate the amount of iron deposition, the main factor of inhibition of deep-water zoobenthos in Lake Onega. During the year, about 40 % of the iron received in the Petrozavodsk Bay is removed from the bay, about 30 % settles to the bottom, and 30 % is constantly present in the water. The distribution of substances in the bay changes significantly throughout the year. During the winter and spring there is a gradual increase in concentrations of allochthonous substances in the bay. After the end of the spring mixing the water of the Petrozavodsk Bay quickly replaced by those of the central reach, and concentrations of substances in the bay and adjacent lake area are aligned.