| Monomethyl mercury (MMHg), a toxic and bioaccumulative form of Hg, is present in some Canadian high and sub Arctic marine mammals at concentrations high enough to pose health risks to Northern peoples using these animals as food. To quantify potentially large sources of Hg to Arctic marine ecosystems, we examined several aspects of Hg cycling in the Canadian Arctic Archipelago (CAA) and Hudson Bay. Firstly, we quantified net Hg inputs to Hudson Bay from atmospheric Hg depletion events (AMDEs). During AMDEs, gaseous elemental Hg(0) (GEM), which is present in the Arctic atmosphere at global background concentrations, is oxidized to inorganic Hg(II) species that deposit to snowpacks. By simultaneously monitoring Hg in the atmosphere and in snowpacks of western Hudson Bay, we demonstrated that most of the Hg(II) deposited during AMDEs is rapidly (photo)reduced and emitted to the atmosphere. Secondly, we examined Hg speciation in marine waters of the CAA and Hudson Bay. We found high concentrations of MMHg and dimethyl Hg (DMHg a toxic, gaseous form of Hg) in deep marine waters, where they are likely produced from Hg(II). Arctic marine waters were also found to be a substantial source of DMHg and GEM to the atmosphere. Thirdly, we quantified Hg exports to Hudson Bay from two major rivers, the Nelson and the Churchill, which have been altered for hydroelectric power production. When landscapes are inundated during river diversion or reservoir creation, microbial production of MMHg is stimulated in flooded soils. Newly produced MMHg can then be exported to downstream waterbodies. We found that annual inputs of total Hg (THg includes both Hg(II) and MMHg) to Hudson Bay from combined Nelson and Churchill River discharge were comparable to inputs from AMDEs. MMHg inputs from river discharge are, however, &sim13 times greater than those from annual snowmelt of Hudson Bay snowpacks. Finally, although combined river and AMDE Hg inputs may account for a large portion of the THg pool in Hudson Bay, these inputs account for a lesser portion of the MMHg pool, thus highlighting the importance of water column Hg(II) methylation as a source of MMHg to Arctic marine foodwebs. |
