Mercury mapping in northern Scandinavian permafrost peatlands

Permafrost is changing rapidly as it continues to thaw, releasing mercury (Hg) and potentially creating hotspots for Hg methylation as organic matter decomposes. If Hg is remobilszed and bioaccumulates as methylmercury (MeHg) in food webs, it could pose a serious health risk to northern communities and wildlife. Here, we have investigated cycling of Hg in five peatlands of northern Scandinavia, that are underlain by sporadic permafrost. To investigate natural thaw gradients, we sampled a total of 47 peat plateau cores that are representing intact permafrost conditions, and 47 fens soil cores, representing thawed permafrost conditions and characterized them based on their distribution of total Hg, MeHg and organic matter. Where permafrost peat had degraded into wet fens, we found that total Hg levels were lower compared to the dry peat plateaus, while MeHg were higher upon thaw. Our results suggest a significant Hg loss and potentially increased methylation due to thermokarst in permafrost-affected peatland ecosystems. A large spatial coverage of sampling locations allows us to investigate the distribution, the variability and transformation of Hg on a regional scale, thereby improving our understanding of Hg mobility from thawing permafrost in northern Scandinavia.