Using lake sediment mercury flux ratios to evaluate the regional and continental dimensions of mercury deposition in arctic and boreal ecosystems

Anthropogenically elevated Hg deposition in arctic and subarctic ecosystems is potentially a serious environmental problem, particularly in northern Europe and North America. To determine the magnitude of this concern, it is necessary to make an evaluation over abroad spatial scale. In the absence of an established network of atmospheric monitoring stations for Hg deposition, we have utilized sediment flux ratios derived from lake sediment profiles throughout the arctic and subarctic to evaluate spatial and temporal patterns of Hg flux to watersheds. Total Hg mass accumulations in layers of Pb-210 dated sediment cores collected from Finland, Sweden; Canada, U.S.A. and Russia were analyzed to construct flux ratios. Flux ratios are calculated by dividing the average recent (i.e. last similar to 10-40 yr) or industrial era Hg flux by an average pre-industrial Hg flux value. Results differ widely across the arctic regions of the northern hemisphere. The highest flux ratios were found in regions associated with strong regional sources of atmospheric Hg emissions such as central and eastern North America and Central Europe. Lakes throughout the U.S. Arctic and the Taimyr Peninsula of Russia showed only slight (similar to 30%) enrichment over background fluxes. Large differences existed in background Hg flux depending on the nature of the watershed geology with some lakes in Alaska exhibiting relatively high concentrations of sediment Hg without evidence of anthropogenic enrichment. In North America, there is a tendency for Hg flux ratios to increase in an southeasterly direction toward the highest concentration of continental emission sources (coal fired power plants. Chlor-alkali plants. metal smelters and waste incinerators). In northern Europe (Sweden and Finland) there is a trend of increasing Hg flux ratios in the north to south direction. Our results suggest that anthropogenic Hg deposition is the dominant regional mercury deposition process in some northern regions but of lesser importance in landscapes highly remote From urban/industrial Hg emissions. Published by Elsevier Science Ltd.