Publication Date:
2016-05-13
Description:
In arctic and sub-arctic environments, mercury (Hg), and more specifically toxic methylmercury (MeHg) is of growing concern to local communities because of its accumulation in fish. In these regions, there is particular interest in the potential mobilisation of atmospherically-deposited Hg sequestered in permafrost that is thawing at unprecedented rates. Permafrost thaw and the resulting ground surface subsidence transforms forested peat plateaus into treeless and permafrost-free thermokarst wetlands where inorganic Hg released from the thawed permafrost and draining from the surrounding peat plateaus may be transformed to MeHg. This study begins to characterise the spatial distribution of MeHg in a peat plateau-thermokarst wetland complex, a feature that prevails throughout the wetland-dominated southern margin of thawing discontinuous permafrost in Canada's Northwest Territories. We measured pore water total Hg, MeHg, dissolved organic matter (DOM) characteristics and general water chemistry parameters to evaluate the role of permafrost thaw on the pattern of water chemistry. A gradient in vegetation composition, water chemistry and DOM characteristics followed a toposequence from the ombrotrophic bogs near the crest of the complex to the poor fens at its downslope margins. We found that pore waters in poor fens contained elevated levels of MeHg and the water draining from these features had dissolved MeHg concentrations 4.5 to 14.5 times higher than the water draining from the bogs. It was determined through analysis of historical aerial images that the poor fens in the toposequence had formed relatively recently (early 1970s) as a result of permafrost thaw. Differences between the fens and bogs are likely to be due to their differences in groundwater function and this suggests that permafrost thaw in this landscape can result in hotspots for Hg methylation that are hydrologically connected to downstream ecosystems.
Print ISSN:
0885-6087
Electronic ISSN:
1099-1085
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
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