Abstract:
Glaciers are retreating across the Canadian Rocky Mountains. As this ice volume is lost, trace elements, nutrients, and other contaminants, accumulated from millennia of atmospheric deposition, are subject to release in glacier meltwater with uncertain consequences for downstream water quality. We monitored and modeled meltwater chemistry at a high temporal resolution using a combination of grab sampling and sondes at the mouth of proglacial Sunwapta River, which drains the Athabasca Glacier in the Canadian Rocky Mountains. Two chemically and temporally distinct sources to melt were distinguished by principal component analysis: a component with a long subglacial residence time characterized by dissolved carbonate-associated elements, and a supra- and englacial component with short subglacial residence time, which contained potential legacy trace elements at low total concentrations and predominantly in a particulate form (total mercury, <3.2 ng/L; total lead, arsenic, and chromium, <2.0 μg/L) and legacy nutrients at moderate concentrations (nitrogen, <0.22 mg/L; phosphorus, <0.03 mg/L). Trace element fluxes and yields were modeled by pairing grab sampling results with correlated high-frequency conductivity or turbidity. Mercury yield (3.2 g/year/km2) was comparable to or lower than yields from other glacial meltwater streams globally. Long-term discharge data suggests that future contaminant yields will increase until peak water is reached, but at present, glacial meltwater does not significantly augment downstream nutrient and trace element contaminant budgets.