Estimation of the capacity for self-purification of transformed rivers of Khanty-Mansi Autonomous Okrug-Yugra (Russia).

This article presents an estimation of the self-purification capacity of rivers flowing through an area of the Ob River basin at Khanty-Mansi Autonomous Okrug-Yugra, which has been significantly transformed by the oil and gas industry. The research was done on the rivers of the Ob River basin in oil fields in 2003-2006 and 2018-2019. The coefficient of mineralization of organic matter has been used as a criterion of the rivers' water self-purification levels. The mineralization coefficient was based on the ratio of numbers of bacteria consuming ammonium nitrogen and polymer substances as well as saprophytic heterotrophic bacteria. According to the results obtained, most rivers draining the oil field area (75% in 2003-2006 and 79% in 2018-2019) were characterized by a low potential for self-purification. The highest level of self-purification criteria was obtained for two rivers: the Ai-Pim River in the Surgut region and the Ovyn'yegan River in the Oktyabrsky region. The high level of self-purification detected with the coeficient of mineralization ensures the maintenance of a certain trophical level and environmental balance of the aquatic ecosystem. Complicated technological processes applied in the oil and gas industry, as well as outdated equipment and poor environmental management, often lead to pipeline accidents and other infrastructure failures. Hazardous pollutants flow into rivers from the watershed area and further into the Gulf of Ob of the Kara Sea. Continuous monitoring of water quality and water resource management based on the results obtained will constitute serious measures to prevent deterioration of aquatic ecosystems. It is necessary to include microbiological parameters in monitoring programs, as this helps to identify the processes of transformation of chemicals found in the river. The use of self-purification assessment methodology for rivers in oil field areas yields effective results in the decision-making process in the sphere of water resource management, significantly reducing ecological risks in the Ob River basin and, as a consequence, in the Arctic region. Integr Environ Assess Manag 2023;19:988-993. © 2022 SETAC.