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.

Fish consumption advisories for mercury (Hg) are common in rivers, highlighting connections between landscape sources of Hg and downstream fluvial ecosystems. Though watershed conditions can influence concentrations of Hg in smaller streams, how Hg changes downstream through larger rivers and how these changes associate with Hg concentrations in fish is not well understood. Here we present a continuum of concentrations and yields of total mercury (THg) and methylmercury (MeHg) from small tributary systems draining diverse western Canadian headwater landscapes through to major transboundary rivers. We associate these downstream patterns with THg concentrations in tissues of resident fish in major rivers. Mean concentrations and yields of unfiltered THg from over 80 monitored tributaries and major rivers were highly variable in space ranging from 0.28 to 120 ng L−1 and 0.39 to 170 µg ha−1 d−1, respectively. Using spatial data and a hierarchical cluster analysis, we identified three broad categories of tributary catchment conditions. Linear mixed modeling analysis with water quality variables revealed significantly lower THg concentrations in tributaries draining cordillera-foothills (geometric mean: 0.76 ng L−1) regions relative to those draining forested (1.5 ng L−1) and agriculturalized landscapes (2.4 ng L−1), suggesting that sources and mobility of THg in soils and surface waters were different between landscapes. However, these concentration differences were not sustained downstream in major rivers as local sources and sinks of THg in river channels smoothed differences between landscape types. Extensive fish tissue monitoring in major rivers and ANCOVA analysis found that site-specific, river water THg and MeHg concentrations and local catchment conditions were stronger associates of THg concentrations in fish than broader trends in rivers within and across landscape classes. Consequently, site-specific, targeted monitoring of THg and MeHg concentrations in water and fish is a preferred study design when assessing regional-level patterns in fish tissue concentrations.

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<p>Mercury (Hg) is a globally dispersed contaminant that can bioaccumulate and biomagnify in food-webs. This research uses a unique combination of measurements in an ice core and a sediment core collected within the same watershed (Lake Hazen, Nunavut, Canada) to determine how the relative importance of Hg inputs from atmospheric and terrestrial sources has changed over the last century. Hg accumulation in Lake Hazen sediment began increasing dramatically in the mid- 1990s, exhibiting a decoupling from atmospheric sources (as estimated from the ice core record), due to the increased importance of remobilized terrestrial Hg inputs to Lake Hazen. Increasing glacier melt and permafrost thaw slumping have increased the delivery of catchment Hg, via glacial rivers, into Lake Hazen. These results show that climate change is likely to slow the recovery of glacierized Arctic watersheds from Hg contamination, countering the anticipated benefit from recent international efforts to reduce anthropogenic Hg emissions.</p>

<p>Anthropogenic activities have resulted in increased mercury (Hg) emissions, and the deposition of inorganic and methyl Hg to watersheds, including those that are glaciated. Alpine glaciers are melting at unprecedented rates due to climate change, with glacier-fed rivers potentially transporting contaminants such as mercury historically archived in glacial ice to downstream proglacial environments. Hg in glacial rivers can also be derived from natural sources such as the erosion of subglacial and proglacial geologic material as glaciers melt and retreat. Furthermore, as inorganic Hg moves downstream, methylation can occur in regions of the watershed that contain wetlands, for example, transforming into it into toxic methyl Hg (MeHg) that can biomagnify in the watershed’s food web.</p><p>We conducted detailed monthly water quality surveys along three major glacial river transects (the Athabasca, North Saskatchewan, and Bow) in the Canadian Rocky Mountains (Banff and Jasper National Parks, Alberta), that included sampling for total and dissolved concentrations of total Hg (THg; all forms of Hg in a sample) and MeHg up to 100 km downstream of glacial termini. The resultant inter-seasonal data, spanning from May to December in this mid-latitude region, will be used to assess the amount of Hg originating from glacial melt in these systems and how it is transformed as it moves downstream. We will also examine contributions of Hg from the erosion of subglacial and proglacial bedrock material. Preliminary results show that THg and MeHg concentrations are very low in these rivers, consistently measuring at less that 3 ng/L. Additionally, as one moves downstream a larger proportion of THg is in the dissolved fraction. MeHg always measured around or below our laboratory’s detection limit (0.01 ng/L) regardless of the sampling location on our river transects.</p><p>The presence of contaminants such as Hg can have negative impacts on freshwater quality, organisms within the watershed, and downstream human populations. Quantifying the amount and speciation of Hg in the headwaters of three primary watersheds in Canada could have important implications for future research and the ongoing challenge of properly planning for drastic climate change effects in glaciated alpine regions despite concentrations of THg and MeHg being so low. </p>