High methylmercury in Arctic and Subarctic ponds is related to nutrient levels in the warming Eastern Canadian Arctic

Permafrost thaw ponds are ubiquitous in the eastern Canadian Arctic, yet little information exists on their potential as sources of methylmercury (MeHg) to freshwaters. They are microbially active and conducive to methylation of inorganic mercury, and are also affected by Arctic warming. This multiyear study investigated thaw ponds in a discontinuous permafrost region in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a continuous permafrost region in the Arctic tundra (Bylot Island, NU). MeHg concentrations in thaw ponds were well above levels measured in most freshwater ecosystems in the Canadian Arctic (>0.1 ng L–1). On Bylot, ice-wedge trough ponds showed significantly higher MeHg (0.3–2.2 ng L–1) than polygonal ponds (0.1–0.3 ng L–1) or lakes (