Snowmelt, glacial and atmospheric sources of mercury in a subarctic mountain lake catchment, Yukon, Canada
Dates
Year
2017
Citation
Zdanowicz, Christian, 2017, Snowmelt, glacial and atmospheric sources of mercury in a subarctic mountain lake catchment, Yukon, Canada: Geochimica et Cosmochimica Acta.
Summary
In montane regions, ongoing and future shrinkage of glacier cover, coupled with a shortening snow cover period, can profoundly alter river hydrology but also lead to the release of airborne contaminants, such as mercury (Hg), deposited and stored in snow and ice. We used field data coupled with hydrological and atmospheric models to estimate and compare the contributions of Hg from snow/glacier melt and from direct atmospheric deposition, to Kusawa Lake, in subarctic Yukon, Canada. The estimated net Hg accumulation rate in supraglacial snow is 0.55 mg m-2 a-1. The modeled net atmospheric flux, including wet+dry deposition, is ~6 times larger, averaging 3.4 mg m-2 a-1, and comparable to the area-averaged meltwater Hg flux into Kusawa [...]
Summary
In montane regions, ongoing and future shrinkage of glacier cover, coupled with a shortening snow cover period, can profoundly alter river hydrology but also lead to the release of airborne contaminants, such as mercury (Hg), deposited and stored in snow and ice. We used field data coupled with hydrological and atmospheric models to estimate and compare the contributions of Hg from snow/glacier melt and from direct atmospheric deposition, to Kusawa Lake, in subarctic Yukon, Canada. The estimated net Hg accumulation rate in supraglacial snow is 0.55 mg m-2 a-1. The modeled net atmospheric flux, including wet+dry deposition, is ~6 times larger, averaging 3.4 mg m-2 a-1, and comparable to the area-averaged meltwater Hg flux into Kusawa Lake (4.5 mg m-2 a-1). The estimated mass of Hg from snow/ice meltwater entering the lake annually is 0.6 kg, while direct atmospheric deposition may contribute a further 0.4 kg, totaling 1.0 kg a-1. Hg levels in cores taken from glaciers in the catchment's headwaters are mostly above expected pre-industrial values, which suggests that some Hg now being released from glaciers is legacy anthropogenic Hg that accumulated in the past ~150 years. Using regional sediment and stream chemistry data, we estimate that the geogenic Hg load in glacial streams that feed Kusawa Lake is much larger than the amount of atmospherically-derived Hg released from melting ice, but most of this geogenic Hg is likely particle-bound, hence not readily bioavailable.