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Arctic soils store 49 Gg mercury (Hg) - an extremely toxic heavy metal, whereas soil Hg can be released to the atmosphere by wildfires. For the first time we investigated the effects of wildfires on the fate of soil Hg in North-Western (NW) Siberia based on GIS maps of areas burned during the last 38 years and a field paired comparison of unburned and burned areas in tundra (mosses, lichens, some grasses, and shrubs) and forest-tundra (multi-layered canopy of larch trees, shrubs, mosses, and lichens). These field surveys were deepened by soil controlled burning to assess the Hg losses from organic horizon and mineral soil. The soil Hg stocks in the organic horizon and in the top 10 cm of the mineral soil were 3.3 ± 0.6 and 16 ± 3 mg Hg m -2 for unburned tundra and forest-tundra, respectively. After the burning by wildfires, the soil Hg stocks decreased to 2.4 ± 0.1 and 6.6 ± 0.2 mg Hg m -2 for tundra and forest-tundra, respectively. By the averages annual burned areas in NW Siberia 527 km 2 , wildfires in tundra and forest-tundra released 0.19 and 2.9 Mg soil Hg per year, respectively, corresponding to 28 % and 59 % of the initial soil Hg stocks. These direct effects of wildfires on Hg volatilization are raised by indirect post-pyrogenic consequences on Hg fate triggered by the vegetation succession and adsorption of atmospheric Hg on the surface of charred biomass. Charred lichens and trees accumulated 4-16 times more Hg compared to the living biomass. Blackened burned vegetation and soil reduced surface albedo and slowly increased soil temperatures in Arctic after wildfires. This created favorable conditions for seeding grasses and shrubs after wildfire and transformed burned high-latitude ecosystems into greener areas, increasing their capacity to trap atmospheric Hg by vegetation, which partly compensate the burning losses of soil Hg., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

In order to evaluate the level of atmospheric pollution in the north of Western Siberia, we studied the composition of urban snow in the vicinity of the Tazovsky settlement as well as in the area of Zapolyarnoye-the largest natural gas field in Russia in terms of a total extraction volume. Our results indicate that anthropogenic activities have caused an increase in electric conductivity and pH values of meltwaters. Concentrations of dissolved and particulate forms of trace elements (Fe, Mn, Ni, Cr, Cu, Pb, Zn, and Cd) were determined using atomic absorption spectroscopy. Dissolved forms of Cd, Zn, and Mn and particulate forms of Cu, Fe, and Ni prevailed in meltwaters of background territories. Human-affected territories were characterized by a predominance of particulate forms of trace elements (except Cd), which indicated increased dust deposition rates. For Cu, Mn, and Fe, mean values of contamination factor (CF) exceeded background levels by 4.4, 4.7, and 6.6 times, respectively. At some sampling sites, concentrations of trace elements exceeded background levels by 10-111 times. The concentration of Zn in our study area was higher than those in other oil and gas fields located in polar and boreal regions. The Cd concentration in the vicinity of the Tazovsky settlement was higher than those in other cities of Western Siberia. The data obtained in the present study on concentrations of soluble and particulate forms of trace elements in snow will be valuable for environmental protection in Russia's Arctic territory.