Trace elements in glacial meltwater at Grand Teton National Park, Wyoming: Contributions from atmospheric deposition and other sources

Abstract:

Glaciers are a reservoir of mercury and other trace elements that have accumulated in the ice from atmospheric deposition during the industrial era. As glaciers continue to melt at an alarming rate, potentially toxic metals are released from the ice to the environment. In order to evaluate the impact of glacier melt on water quality in high elevation catchments in Grand Teton National Park, we sampled transects along the Teton and Middle Teton glaciers and proglacial streams during early-July and mid-August 2013. The glaciers were snow-covered during July, and thus water samples were primarily melt of snowpack from the previous winter. During August, the glacier ice was exposed across the ablation zone. The contrasting sample sets from July and August allowed for a comparison of water chemistry of snowmelt and glacier melt, respectively. The Teton Glacier transect included ten sample sites: four samples of surface drainage on the glacier, three near the terminal moraine, and three in Glacier Gulch stream. The Middle Teton transect included thirteen sample sites: one above the glacier, four of surface drainage on the glacier, two near the terminal moraine, two at the moraine of adjacent Teepe Glacier, and four in Garnet Canyon stream. All water samples were analyzed for total and methyl mercury, a suite of trace elements (including U, Sr, and Mn), solutes, and stable water isotopes (δ²H and δ¹⁸O). A subset of samples were analyzed for tritium to differentiate recent snowmelt from older ice melt. Preliminary results indicate that snowmelt and glacier melt were a significant source of total mercury, with little additional inputs downstream of the glaciers. Methyl mercury concentrations increased downstream of the glaciers, possibly indicating that mercury from the glaciers undergoes methylation in the proglacial streams. Other trace elements were found in low concentrations in melt water, but increased substantially downstream of the glaciers likely due to water-rock interactions. This study has implications for evaluating the relative impacts of atmospheric deposition, weathering, and other trace element sources to high alpine lakes and streams.