Abstract
ABSTRACTGlaciers are reservoirs of atmospherically deposited trace elements that are released during melt. Weathering in glacial environments also contributes solutes to proglacial streams. To investigate the relative importance of atmospheric deposition and weathering on trace element chemistry of glacial streams, we sampled supraglacial and proglacial meltwater at two glacierized catchments in Grand Teton National Park, Wyoming, which is located downwind of agricultural/industrial emissions and dust sources. Concentrations of major ions (Mg2+, K+, Na+, Ca2+, SO4 2−), alkalinity, conductivity, and a subset of trace elements (U, Mo, Sr, Rb, Li, Ba) were low in supraglacial meltwater but increased in proglacial streams because of water-rock interactions. In contrast, concentrations of the trace metals Mn, Co, Zn, Pb, Cd, and Hg had relatively high concentrations in supraglacial meltwater and decreased downstream. These metals are not abundant in the local bedrock and thus are likely sourced from atmospheric deposition. Stable isotopes indicated different water sources in July (snowmelt-dominated) and August (ice melt-dominated), but water chemistry was similar during both months, indicating similar composition of recent snowfall and older ice. These findings have implications for evaluating the relative impacts of atmospheric deposition and weathering in glacier- and snow-dominated catchments.
Highlights
The retreat of glaciers worldwide may lead to the rapid release of trace metals that are stored in the ice (Schuster et al, 2002; Barbante et al, 2004; Hong et al, 2004; Fortner et al, 2005, 2009)
Stable isotopes of H and O (δ18O) show that the Garnet Canyon and Glacier Gulch watersheds are dominated by meltwater inputs because proglacial stream and moraine meltwater samples have similar isotopic ratios as supraglacial meltwater (Fig. 4)
Supraglacial meltwater isotope values were variable within each month, but overall were more enriched in August relative to July
Summary
The retreat of glaciers worldwide may lead to the rapid release of trace metals that are stored in the ice (Schuster et al, 2002; Barbante et al, 2004; Hong et al, 2004; Fortner et al, 2005, 2009). Metals and other solutes released from the thawing cryosphere can impact the hydrologic system, resulting in changing water chemistry because of melting glaciers (Salerno et al, 2016), permafrost (Schuster et al, 2011;Todd et al, 2012), and rock glaciers (Thies et al, 2007).Trace metals are deposited in alpine environments via wet and dry atmospheric deposition, with important contributions from windblown dust (Reynolds et al, 2010; Carling et al, 2012) and industrial activities (Hong et al, 2004). Receding glaciers expose readily weathered fresh bedrock and glacial till that may contribute to elevated metal concentrations in proglacial streams (Fortner et al, 2011). As the rate of glacier melt continues to accelerate, trace metal concentrations in meltwater need to be evaluated for contributions from atmospheric deposition and interactions with freshly weathered bedrock in the proglacial environment
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