Mercury in freshwater ecosystems of the Canadian Arctic: Recent advances on its cycling and fate

Abstract

The Canadian Arctic has vast freshwater resources, and fish are important in the diet of many Northerners. Mercury is a contaminant of concern because of its potential toxicity and elevated bioaccumulation in some fish populations. Over the last decade, significant advances have been made in characterizing the cycling and fate of mercury in these freshwater environments. Large amounts of new data on concentrations, speciation and fluxes of Hg are provided and summarized for water and sediment, which were virtually absent for the Canadian Arctic a decade ago. The biogeochemical processes that control the speciation of mercury remain poorly resolved, including the sites and controls of methylmercury production. Food web studies have examined the roles of Hg uptake, trophic transfer, and diet for Hg bioaccumulation in fish, and, in particular, advances have been made in identifying determinants of mercury levels in lake-dwelling and sea-run forms of Arctic char. In a comparison of common freshwater fish species that were sampled across the Canadian Arctic between 2002 and 2009, no geographic patterns or regional hotspots were evident. Over the last two to four decades, Hg concentrations have increased in some monitored populations of fish in the Mackenzie River Basin while other populations from the Yukon and Nunavut showed no change or a slight decline. The different Hg trends indicate that the drivers of temporal change may be regional or habitat-specific. The Canadian Arctic is undergoing profound environmental change, and preliminary evidence suggests that it may be impacting the cycling and bioaccumulation of mercury. Further research is needed to investigate climate change impacts on the Hg cycle as well as biogeochemical controls of methylmercury production and the processes leading to increasing Hg levels in some fish populations in the Canadian Arctic.

Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

“…The frozen soils of permafrost have historically been considered a barrier to the movement of contaminants and many waste and dump sites use containment strategies that rely on the low mobility of contaminants in permafrost soils (Grannas et al, 2013). However, the warming Arctic climate may lead to an increased mobility of contaminants, either stored in soils at waste sites or historically accumulated in permafrost, into Arctic surface waters (Armitage and Wania, 2013;Chételat et al, 2014).…”

Relating Fish Hg to Variations in Sediment Hg, Climate and Atmospheric Deposition

“…In lakes, fish uptake of Hg varies by, e.g., extent and type of lake input from land and atmospheric sources, and by lake size and morphology. Daily, seasonal and annual water-intake and related aeration and de-aeration dynamics affect in-lake trophic bioaccumulation of methyl Hg directly [67]. For example, increased Hg uptake by fish would occur through increased net Hg methylization as hypolimnetic water temperatures and biological oxygen demands rise from cool to warm [68].…”

Dried Blood Spot Sampling of Landlocked Arctic Char (Salvelinus alpinus) for Estimating Mercury Exposure and Stable Carbon Isotope Fingerprinting of Essential Amino Acids

“…These long‐term data sets, and others like them, indicate that mean muscle total Hg concentrations ([THg]) in resident and landlocked Arctic char vary greatly among populations (approximately 0.01–1 µg/g wet wt; Barst et al 2019). The drivers of this variation are the topic of ongoing research and may involve differences in Hg inputs, Hg methylation rates, water chemistries, and/or food‐web relationships among aquatic systems (Lescord et al 2015; Chételat et al 2015, 2017; Hudelson et al 2019).…”