Methylmercury production and export in permafrost peatland catchments of the Taiga Plains
Lauren Thompson, University of Alberta
Ongoing permafrost thaw in northern peatland catchments may increase the production and downstream delivery of neurotoxic methylmercury across the terrestrial-aquatic continuum. Peatlands in boreal-Arctic regions have large stocks of mercury in frozen soils, accumulated through atmospheric deposition of natural and human-emitted mercury over thousands of years. Permafrost thaw in peatlands may shift environmental conditions to facilitate microbial production of methylmercury (methylation). However, the degree to which mercury is methylated post-thaw and exported downstream remains uncertain in northwestern Canada and poses a potential hazard for uptake by aquatic food webs.
Here, we examined methylmercury cycling throughout the peatland-rich Interior Plains of boreal western Canada. We explored the microbial production of methylmercury in thawed wetlands compared to intact permafrost peatlands. Secondly, we determined how discharge and land cover controlled the export and concentrations of methylmercury in stream catchments with differing peatland extent. Findings suggest that permafrost thaw in northern peatlands can enhance mercury methylation across the landscape. However, wetland trophic status and groundwater connectivity control methylmercury production and catchment hydrological functioning will determine the degree of downstream export. This knowledge is important for public health planning and land use intervention in the face of climate change, given the high risks of methylmercury in aquatic ecosystems to northern communities.
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