Mercury in the Background Tundra Soils of the Northeastern European Russia

The mercury (Hg) accumulation and migration in Arctic ecosystems is most relevant in the context of ever-increasing anthropogenic impact and climate change, potentially enhancing the transformation of Hg compounds and their involvement in biogeochemical cycles. We report the results of a comprehensive study of the background Hg content, its vertical distribution, and the factors determining Hg accumulation in different types of tundra soils in the northeastern European Russia. The Hg content is determined using atomic absorption spectrometry with pyrolysis of samples and GIS technologies as a tool for analysis of the spatial distribution of Hg. As is shown, spatial heterogeneity of the Hg distribution in tundra soils is determined by a complex effect of the soil physicochemical properties. The peat and gley horizons enriched with organic matter and physical clay fraction are the most efficient Hg accumulators, whereas in podzols active vertical migration of Hg takes place under conditions of a percolative soil water regime. We suggest that the threshold limit values of Hg should be based on a 95% confidence interval to standardize the regional background Hg concentrations. This allows us to take into account natural background fluctuations and to exclude extreme. The maximum threshold limit values of Hg content are observed in bod-podzolic (230–260 μg/kg), surface-gley tundra (240 μg/kg), and peaty-gley tundra (230 μg/kg) soils. These results are important for evaluating the background Hg levels, developing environmental protection measures, and predicting changes in the Hg behavior in the context of permafrost degradation and alterations in hydrothermal regime.