Box 6 – Mercury in Peatlands
In many northern peatlands, mercury is considered a contaminant of concern where its bioavailability and ability to bioaccumulate in food webs is dependent on the source of groundwater and internal hydrology of a peatland (Branfireun et al., 2020). Gaseous elemental mercury has an atmospheric residence time of several months, which enables its global distribution and eventual deposition into ecosystems, often far from its original source.
The saturated, highly organic soils common in peatlands harbor a diversity of anaerobic microbes, particularly sulfate reducers and methanogens, which facilitate the transformation of deposited and/or stored inorganic mercury into methylmercury (Bishop et al., 2020). Methylmercury is a bioaccumulating neurotoxin that has been linked to adverse environmental and human health outcomes (Beckers and Rinklebe, 2017). Peatlands with weaker groundwater connectivity (i.e., bogs and poor fens) are often strong methylmercury sources in landscapes; while, more minerotrophic peatlands like rich fens or swamps can be net methylmercury sinks (Tjerngren et al., 2012). In general, the coverage of peatlands in many northern landscapes is often associated with increasing methylmercury concentrations in fish and other wildlife that local communities, such as indigenous communities in the James Bay Lowland, may rely on as a food source.