TRACE METALS IN GLACIAL MELTWATER AND PROGLACIAL STREAMS AT GRAND TETON NATIONAL PARK, WYOMING

Glaciers are an important reservoir of mercury (Hg) and other toxic metals that have accumulated in the ice during the industrial era. As glaciers continue to melt at an alarming rate, these metals are released to the environment. Furthermore, high weathering rates in the glacial environment and increased flows from glacier melt may facilitate trace metal transport in proglacial streams. During the summer of 2013 we sampled glaciers and proglacial streams in the Teton Range of Wyoming, which is located downwind of major industrial emission and dust sources, to investigate the relative importance of atmospheric deposition and weathering on water quality in glacier-fed streams. The sampling included transects along the Teton and Middle Teton glaciers and proglacial streams during early-July, when the glaciers were snow-covered, and mid-August, when the glacier ice was exposed. The contrasting sample sets allowed for a comparison of water chemistry of snowmelt and glacier melt, respectively. Water samples were analyzed for total Hg (THg) and methyl Hg (MeHg), a suite of trace elements, solutes, and stable water isotopes (δ²H and δ¹⁸O). A subset of samples were analyzed for tritium (³H) to differentiate recent snowmelt from older ice melt. Results show that water in the proglacial streams was isotopically depleted in July relative to August, indicating that snowmelt was the dominant water source in July and glacier melt was dominant in August. However, trace metal concentrations were similar during both months. Snowmelt and glacier melt were a significant source of THg, with little additional inputs downstream of the glaciers. Concentrations of MeHg, the most toxic and bioavailable form of Hg, increased downstream from the glaciers, possibly indicating active Hg methylation in the proglacial streams. Concentrations of other trace elements, including U, Sr, Rb, and Li, were low 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, and may serve as a small-scale example of much larger glacier systems in Alaska and elsewhere.