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Elevated stream trace and minor element concentrations in the foreland of receding tropical glaciers |
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| Authors: | Sarah K Fortner Bryan G MarkJeffrey M McKenzie Jeffrey BuryAnnette Trierweiler Michel BaraerPatrick J Burns LeeAnn Munk |
| Institution: | a Byrd Polar Research Center, The Ohio State University, 1090 Carmack Drive, Columbus, OH 43210, USA b Department of Earth and Planetary Science, McGill University, 3450 University Avenue, Montreal PQ, Canada H3A 2A7 c Department of Environmental Studies, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA d Department of Geological Sciences, University of Alaska Anchorage, 3101 Science Circle, Anchorage, AK 99508, USA |
| Abstract: | Globally, the ongoing retreat of mountain glaciers will ultimately diminish fresh water supplies. This has already begun in watersheds with greatly reduced glacial coverage. Still unknown are the affects of glacial retreat on downstream water quality, including the threats to human and ecosystem health. In the Cordillera Blanca, retreating glaciers have exposed sulfide-rich rock outcrops, negatively affecting the quality of the glacial meltwater. This study has evaluated glacial melt stream hydrogeochemistry in the sulfide-bearing Rio Quilcay watershed (∼9°27′S, ∼77°22′W) during the 2008 dry season. Surface water samples were collected from the upper 12 km of the watershed during the 2008 dry season. Dissolved (0.4 μm) and unfiltered acidified (pH < 2) Al, Co, Cu, Fe, Ni, Mn, Pb, Zn and dissolved major ions and organic C (DOC) concentrations were quantified and pH and temperature were measured in the field. Twenty of 22 stream samples had pH values below 4, generating significantly (p < 0.01, α = 0.05) greater cation denudation normalized to discharge than other worldwide glacier-fed streams. Additionally, dissolved trace and minor element concentrations were comparable to acid mine drainage. Non-conservative dissolved element behaviors resulted from adsorption/desorption reactions in tributary mixing zones. At low pH values, hydrous Fe oxides acted as the dominant sorption surfaces. The poor water quality observed in Cordillera Blanca headwaters coupled with the likely exposure of additional sulfide-rich outcrops from ongoing glacial retreat may pose water quality challenges. |
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