Unprecedented Increases in Total and Methyl Mercury Concentrations Downstream of Retrogressive Thaw Slumps in the Western Canadian Arctic

Abstract

Retrogressive thaw slumps (RTSs) are thermokarst features created by the rapid thaw of ice-rich permafrost, and can mobilize vast quantities of sediments and solutes downstream. However, the effect of slumping on downstream concentrations and yields of total mercury (THg) and methylmercury (MeHg) is unknown. Fluvial concentrations of THg and MeHg downstream of RTSs on the Peel Plateau (Northwest Territories, Canada) were up to 2 orders of magnitude higher than upstream, reaching concentrations of 1,270 ng L–1 and 7 ng L–1, respectively, the highest ever measured in uncontaminated sites in Canada. MeHg concentrations were particularly elevated at sites downstream of RTSs where debris tongues dammed streams to form reservoirs where microbial Hg methylation was likely enhanced. However, > 95% of the Hg downstream was typically particle-bound and potentially not readily bioavailable. Mean open-water season yields of THg (610 mg km–2 d–1) and MeHg (2.61 mg km–2 d–1) downstream of RTSs were up to an order of magnitude higher than those for the nearby large Yukon, Mackenzie and Peel rivers. We estimate that ∼5% of the Hg stored for centuries or millennia in northern permafrost soils (88 Gg) is susceptible to release into modern-day Hg biogeochemical cycling from further climate changes and thermokarst formation.

Thermokarst Effects on Carbon Dioxide and Methane Fluxes in Streams on the Peel Plateau (NWT, Canada)

“…RTSs develop due to ablation of exposed, ice‐rich permafrost, causing rapid thaw of thick layers of frozen ground and transport of large volumes of saturated thawed materials from slopes to fluvial systems (Kokelj et al, ; Figure ). In addition to mobilizing previously sequestered material into modern biogeochemical cycles, RTS can temporarily alter hydrology if the debris tongue (Figure ) partially dams the impacted stream, creating a transient upstream reservoir (Kokelj et al, ; St. Pierre et al, ).…”

Potential impacts of mercury released from thawing permafrost

“…However, the greatest Hg losses occur only in thawed areas with large amounts of frozen carbon, specifically the lower YRB near the delta and the upper Mackenzie basin in Canada. This estimate does not account for Hg losses in areas susceptible to thermokarst or soil collapse during thaw, which our model does not include 27 . RCP85 showed extensive thaw everywhere with small Hg losses in areas with little frozen carbon, such as the Brooks Range, and the largest Hg losses in areas with the most frozen carbon, like the North Slope, Alaska.…”

The importance of continuous dialogue in community-based wildlife monitoring: case studies of dzan and łuk dagaii in the Gwich’in Settlement Area

“…Although variation exists in the extent of migrations, a single individual may use multiple of these habitats in a lifetime (Thompson and Millar 2007;VanGerwen-Toyne et al 2008;Harris et al 2012). As a result, this species could encounter changing conditions throughout the Mackenzie River watershed, including changes to river habitats through thawing permafrost and altered hydrology (St. Pierre et al 2018), the potential for Pacific salmon colonization (Dunmall et al 2016), and shifts in ocean productivity (Ardyna et al 2014). In response to watershed changes, community members raised questions regarding various fish species, including broad whitefish.…”

“…Climate change and industrial development are rapidly transforming the structure and function of northern ecosystems (Raynolds et al 2014;Kokelj et al 2015;St. Pierre et al 2018;Lewkowicz and Way 2019), and these changes have the potential to impact northern livelihoods and cultural traditions by altering fish and wildlife habitat and impeding human access to sustenance species (Goldhar et al 2014;Brinkman et al 2016;Brown et al 2018;Turner et al 2018).…”