Wildfire effects on mercury fate in soils of North-Western Siberia.

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 km2, 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.

Distribution of dissolved trace elements in the Laptev Sea affected by the Lena River discharge.

This study presents new data on concentration of dissolved trace elements (DTE) in the Lena River-Laptev Sea mixing zone. Mean concentrations of some dissolved heavy metals in the mixing zone of fresh waters of the Lena River and sea waters of the Laptev Sea on the middle shelf and on the outer shelves are: 0.7± 0.05 µÐœ and 0.5 ± 0.04 µÐœ for Fe, 0.06 ± 0.01 µÐœ and 0.07 ± 0.01 µÐœ for Ni, 0.01 ± 0.003 µÐœ and 0.003 ± 0.002 µÐœ for Zn, 59.2 ± 7.4 nМ and 73.4 ± 12.8 nМ for Cu, respectively. Two major groups of DTE distribution were revealed according to their spatial behavior. The Li, V, As, Rb, Sr, Mo, U concentrations increase towards the outer shelf with increasing salinity. In contrast, mean concentrations of Al, Ti, Mn, Fe, Co decrease with increasing distance from the coast. The identified transport of freshwaters to a distance of 400 km is reflected in the distribution of DTE, which suggests that these elements are able to reach to the Central Arctic Ocean.