Exploring patterns of hydrochemical alterations below melting glaciers in Peru in long-term samples of stream water

Authors: Bryan Mark*, The Ohio State University, Alex Eddy, 1US National Park Service, Sierra Nevada Inventory and Monitoring Network, Three Rivers, CA, USA, Michel Baraer, University of Quebec, ETS, Montreal, Canada, Jeffrey McKenzie, McGill University, Alfonso Fernandez, University of Concepcion, Susan Welch, Ohio State University
Topics: Mountain Environments, Cryosphere, Water Resources and Hydrology
Keywords: Glaciers, Andes, Peru, water, hydrochemistry, water quality, isotopes
Session Type: Paper
Day: 4/6/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: Truman, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Glaciers in the tropical Andes continue to recede after decades of negative mass balance, impacting the downstream hydrology and water quality. Efforts to quantify the historical progression of this hydrological transformation have been hampered by a lack of long term observations of all components of the water cycle. This study integrates hydrochemical analysis and spatial exploration across multiple scales and utilizes a unique sample set that comprises over a decade of annual repeat measurements from synoptically sampled streams discharging the glacier-fed tributary watersheds to the Santa River. Using measurements of stable water isotope ratios, we associate hydrochemical variation with relative changes in glacierized area. Routinely sampled hydrological endmembers including surface streams, glacier meltwater and groundwater springs during the dry season. To differentiate the influence of elevation, we obtained shallow groundwater springs from the non-glacierized Cordillera Negra to derive a local meteoric elevation effect. We compared results from samples taken in 2014-16 with those taken from 2004-06. The chemistry of proglacial surface waters is primarily determined by weathering in rock-water contact areas, and glacial meltwater inherits the chemical properties of the surficial lithology along a flow path. Dominant hydrochemical processes include silicate weathering, coupled pyrite oxidation with silicate weathering, and to a lesser extent, carbonate weathering. The sulfate constituent is unusually high for portions of the study region and is attributed to highly acidified waters immediately downstream from glacial point sources.

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