ENVIRONMENTAL ASSESSMENT OF WATER QUALITY IN THE ONEGO LAKE URBAN TRIBUTARY BY CHEMICAL INDICATORS

Abstract

Introduction. The Lososinka River is an urban tributary of Lake Onego, the lower reaches of which flow through the territory of Petrozavodsk city, receiving untreated drains of the city’s storm sewers. The river enters the Petrozavodsk Bay of Lake Onego, which is used as a source of public drinking water supply in the city. Methods. During the 2015 open water period, the oxygen concentration, total iron, color, pH, total suspended matter, biochemical oxygen demand (BOD5), content of oil products, and dichromate chemical oxygen demand were measured by standard methods in the water of the background and urban areas of the Lososinka River. Results. In the river water, high values of water color (132 mg/l Cr-Co), total iron (1.5 mg/l), dichromate chemical oxygen demand (23 mgO/l) were revealed, which is associated with the geochemical peculiarities of the surface waters in Karelia, enriched in the humic matter. Seasonal increases in the concentrations of these indicators were associated with floods. The oxygen saturation of the water reached 90% due to the fast current and riffles. The indicators of water pollution include total phosphorous (60 μg/l), mineral phosphorous (40 μg/l), BOD5 (1.5 mgO2/l), suspended matter (25.5 mg/l), and content of oil products (0.02 mg/l). Seasonal changes in these indicators were not associated with the hydrological regime of the river. In the storm sewers of the city, the maximum permissible concentrations for BOD5 are exceeded by 4 times, and for oil products — by 15 times. The Kruskal–Wallis test showed that all the studied chemical indicators in the urban and background areas of the river do not have significant differences. Conclusion. Water quality in the Lososinka River is considered satisfactory in terms of most of the studied parameters. According to the total iron content, the water is characterized as polluted, and according to water color, the river water is classified as dirty. The maximum permissible concentrations for total iron in the background and urban areas of the river were exceeded by 10 times. The standards for water quality adopted in the Russian Federation and the maximum permissible concentrations for total iron and water color are inapplicable for the water bodies in Karelia with high background values of these indicators. The trophic status of the river corresponds to the eutrophic state. Good saturation of the river water with oxygen hinders water pollution in the city territory due to self-purification processes.