Introduction to the Special Series "Environmental Monitoring on Global and Local Scales".

The ecosystems of Siberia provide valuable services to the human population and afford important climate feedback. However, they are subject to anthropogenic pressures leading to the transformation of ecosystem structure and functions such as deforestation; extraction and transportation of fossil hydrocarbons; mining, refining, and smelting industrial activities; damming of rivers by high-pressure hydroelectric plants, and other activities. The articles in this special series deal with the monitoring of natural ecosystems of Siberia that are located on vast areas of Eurasia, many of which are hard to reach and sparsely populated. The results and approaches of environmental monitoring presented in this special series offer new opportunities for developing the strategy of intelligent management and conservation of vulnerable Siberian ecosystems to meet the challenges of global climate change and unsustainable use of natural resources. Integr Environ Assess Manag 2023;19:970-971. © 2023 SETAC.

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 Complicated technological processes applied in the oil and gas industry, as well as outdated equipment and poor environmental management, often lead to pipeline accidents and other infrastructure failures.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.

Anthropogenic and natural hydrocarbons in water and sediments of the Kara Sea.

The results on the content and composition of aliphatic (AHСs) and polycyclic aromatic hydrocarbons (PAHs) at the geochemical barrier between the Kara Sea and the Ob and Yenisei Rivers are discussed in comparison with those in the mouth areas of the Lena, Khatanga, Indigirka and Kolyma. It has been established that hydrocarbon concentrations sharply decrease in the river-sea mixing zones, and their composition, and the ratio of their dissolved and suspended forms change. Besides, the research season plays a great role, as the highest content of hydrocarbons and particulate matter was found in the Ob Gulf during the flood, when the concentrations of AHCs in surface waters reached 325 µg/L, PAHs -15 ng/L, particulate matter-15.5 mg/L. In the Kara Sea itself, AHC concentrations increased on average from 20 to 59 µg/L, that is most likely associated with the melting of seasonal ice and floods. Anthropogenic influence was found in river waters, where the proportion of naphthalenes, which marks oil products, and pyrene, which marks pyrogenic PAHs, is increased. In the Ob Gulf is linked to an increase in navigation along the Northern Sea Route and the functioning of the port of Sabetta. In the mouth area of the Yenisei, the concentrations of both AHC and PAH in surface waters and sediments varied in a smaller range than in the mouth area of the Ob, which is due to the nature of the rocks that make up the catchment areas of these rivers, as well as the regulation of the Yenisei runoff. The hydrological features of the estuarine areas can lead to increased AHC concentrations (the mouth of the Khatanga, up to 189 µg/L, 2.6 µg/mg SPM). The minimum AHC content in SPM and sediments in the river transects was established in the East Siberian rivers (Indigirka, Kolyma), associated with the decreasing productivity in waters from the Western Arctic seas to the Eastern.