Drivers of Mercury Cycling in the Rapidly Changing Glacierized Watershed of the High Arctic’s Largest Lake by Volume (Lake Hazen, Nunavut, Canada)

Abstract

Across the Arctic, glaciers are melting and permafrost is thawing at unprecedented rates, releasing not only water to downstream aquatic systems, but also contaminants like mercury, archived in ice over centuries. Using concentrations from samples collected over 4 years and calibrated modeled hydrology, we calculated methylmercury (MeHg) and total mercury (THg) mass balances for Lake Hazen, the world's largest High Arctic lake by volume, for 2015 and 2016. Glacial rivers were the most important source of MeHg and THg to Lake Hazen, accounting for up to 53% and 94% of the inputs, respectively. However, due to the MeHg and THg being primarily particle-bound, Lake Hazen was an annual MeHg and THg sink. Exports of MeHg and THg out the Ruggles River outflow were consequently very low, but erosion and permafrost slumping downstream of the lake increased river MeHg and THg concentrations significantly before entering coastal waters in Chandler Fjord. Since 2001, glacial MeHg and THg inputs to Lake Hazen have increased by 0.01 and 0.400 kg yr -1 , respectively, in step with dramatic increases in glacial melt. This study highlights the potential for increases in mercury inputs to arctic ecosystems downstream of glaciers despite recent reductions in global mercury emissions.

A revised pan-Arctic permafrost soil Hg pool based on Western Siberian peat Hg and carbon observations

“…While the stock of C in Arctic and sub-Arctic peat and mineral soils is fairly well quantified (472 Pg C; 95 % confidence interval, CI, of ±27 Pg) in the upper 0-1 m (Hugelius et al, 2014), this is not true for pollutants such as mercury (Hg). Because of its strong bioamplification in Arctic marine biota (Morel et al, 1998) and exposure to native Arctic populations (AMAP, 2011), there is a strong interest in understanding Hg biogeochemistry in Arctic environments (Outridge et al, 2008;Steffen et al, 2008;Stern et al, 2012). Recent advances in quantifying Arctic Hg cycling show that Arctic Hg II wet deposition is generally low (Pearson et al, 2019) and that the vegetation Hg pump drives yearlong net gaseous Hg 0 (and CO 2 ) deposition via foliar uptake to Arctic vegetation and litterfall to soils (Obrist et al, 2017;Jiskra et al, 2018Jiskra et al, , 2019.…”

Contrasting the ecological effects of decreasing ice cover versus accelerated glacial melt on the High Arctic's largest lake

“…Examples include alterations to thermal structure [3], turbidity [4], nutrient concentrations [5] and the mobilization and release of stored pollutants such as metals (e.g. mercury) and organic contaminants [6][7][8].…”

Quantifying Meltwater Sources and Contaminant Fluxes from the Athabasca Glacier, Canada

“…Sunwapta River trace element concentrations were comparable to other small proglacial streams in alpine North America, the circum-Arctic, and Antarctica, where Hg concentrations are typically less than 8 ng/L. ,,,,− For example, trace element concentrations were also low in Wyoming proglacial streams (As < MDL; Cr < MDL; Cu < 6 μg/L; Pb < 7 μg/L; Zn < 20 μg/L). , In contrast, small proglacial systems in central east Asia have a greater range of THg concentrations (<MDL to 230 ng/L). − , …”

“…The annual THg yield for the Sunwapta River headwaters (2.4–4.0 g/km 2 /year; Table ) is comparable to other small glaciated catchments globally and comparable to small North American catchments in forested, wetland, urban, and agricultural settings but is approximately an order of magnitude higher than THg yields for major Canadian watersheds (Table S6). THg yields of small glaciated catchments are up to 19.9 g/km 2 /year and as low as 0.2–0.5 g/km 2 /year. , Few studies have calculated yields of other trace element contaminants in glaciated catchments; this hinders comparison of trace element yields between glaciated catchments and catchments in different geographic or physiographic settings. Typical THg yields of forested, wetland, urban, and agricultural catchments under 3000 km 2 are less than 5.5 g/km 2 /year (Table S6).…”