Hydrochemical Signatures of Glacial Meltwater on Volcán Chimborazo, Ecuador

Abstract

Glacier recession in the tropical Andes is generating significant concern over future water availability for domestic use, irrigation, and hydropower. Sparse data sets, extreme heterogeneity in climate patterns, and the limited understanding of groundwater and ecohydrological processes in these catchments make predicting the hydrologic response to glacier retreat difficult. Here I examine a glaciated watershed on Volcán Chimborazo, Ecuador. I use geospatial analysis and recent geologic studies to evaluate the vegetation and geologic factors that influence the hydrologic response of the watershed. Additionally, I utilize hydrochemical and stable isotope signatures to investigate how melt and groundwater contributions to streamflow have changed over time along with possible meltwater-groundwater connections. A new landcover map of Volcán Chimborazo, generated using object based image analysis, reveals a significant increase in the upper limit of vegetation on the mountain and expansion of crop and pasture land since 1978. Geologic cross-sections, based on recent studies, show that near surface geology is dominated by glacial deposits and underlain by relatively young volcanic bedrock. Results from a hydrochemical mixing model (HBCM) combined with discharge measurements reveal spatial variability in groundwater discharge and suggest that groundwater discharge during the dry season has decreased from 2012-2017. Short time scale variability is clearly influenced by precipitation, but long-term discharge trends remain uncertain. Lastly, stable isotope and solute concentrations in samples suggest groundwater in the study watershed is recharged by precipitation falling at high elevations where ice and snow may dominate the hydrologic system.