Hydrogeochemical characterization of glacierized volcanic watersheds in the subhumid inner tropics
Abstract
Climate change will impact world water supply, resulting in water insecurities among vulnerable communities. Mountain glaciers in the tropics are particularly vulnerable, as the fastest rates of warming are predicted in high altitude, low latitude regions. Current observations indicate a decrease in streamflow in many tropical glacierized watersheds in the Andes, where 99% of tropical glaciers are located. Much previous work has focused on the outer tropics, where seasonal precipitation is strong and watersheds are underlain by crystalline bedrock. Here, we investigate three Ecuadorian watersheds in the subhumid inner tropics, where seasonal changes in precipitation are less pronounced, leading to year-round ablation. Further, these watersheds are located on Volcán Chimborazo and Volcán Cayambe, where field observations of fractured volcanic bedrock raise the hypothesis that groundwater flow may be more substantial than in many of the previously studied crystalline-cored watersheds. Study of Volcán Chimborazo and Volcán Cayambe will expand our understanding of hydrologic responses to glacier retreat to a greater range of climatic and geologic conditions. Within volcanic settings in the inner tropics, we compare three watersheds to probe how precipitation and glacial conditions influence changes in glacier melt contribution to streamflow. The Río Chimborazo watershed on Volcán Cayambe is substantially dryer than both the Río Mocha watershed on Volcán Chimborazo and the Río La Dormida watershed on Volcán Cayambe. Río La Dormida and Río Chimborazo have five times less fractional ice coverage than Río Mocha. These discrete differences among otherwise similar watersheds enables us to isolate the impacts of climate and ice cover on glacial, groundwater, and surface-water contributions to streamflow. In an end-member mixing model designed for data-sparse watersheds, dissolved ions and stable water isotopes serve as tracers to parse out and quantify water sources, namely glacier melt and groundwater. We characterize the mineral geochemistry of bedrock and soil using XRD analysis to learn where these dissolved ions originate. From this, we infer flow paths that influence the contributions of meltwater and groundwater to streamflow in the watersheds.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H43K2178N
- Keywords:
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- 1807 Climate impacts;
- HYDROLOGY;
- 1830 Groundwater/surface water interaction;
- HYDROLOGY;
- 1834 Human impacts;
- HYDROLOGY;
- 1879 Watershed;
- HYDROLOGY