Using synoptic tracer surveys to assess runoff sources in an Andean headwater catchment in central Chile
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Headwater catchments in the Andes provide critical sources of water for downstream areas with large agricultural communities dependent upon irrigation. Data from such remote headwater catchments are sparse, and there is limited understanding of their hydrological function to guide sustainable water management. Here, we present the findings of repeat synoptic tracer surveys as rapid appraisal tools to understand dominant hydrological flow paths in the semi-arid Rio Grande basin, a 572-km2 headwater tributary of the 11,696-km2 Limarí basin in central Chile. Stable isotopes in stream water show a typical altitudinal effect, with downstream enrichment in δ2H and δ18O ratios. Seasonal signals are displayed in the isotopic composition of the springtime melting season water line with a steeper gradient, whilst evaporative effects are represented by lower seasonal gradients for autumn and summer. Concentrations of solutes indexed by electrical conductivity indicate that there are limited contributions of deeper mineralised groundwater to streamflow and that weathering rates vary in the different sub-catchments. Although simplistic, the insights gained from the study could be used to inform the structure and parameterisation of rainfall runoff models to provide seasonal discharge predictions as an evidence base for decision making in local water management.
KeywordsTracers Stable isotopes Mountainous runoff generation Andes Semi-arid central Chile Steep elevation gradient
Funding for field visits was provided by the BMBF (German Federal Ministry for Education and Research) in the scope of the research projects “Web based drought information system” and “Increasing water use efficiency in irrigation management” (2012–2014). We especially thank our local project partners from the University of La Serena: Pablo Álvarez, Fabián Reyes and Nicole Kretschmer from the Centre for Advanced Studies in Arid Regions (CEAZA). Their support and hospitality were of key importance to be able to carry out the sampling campaigns. We also thank Christoph Schüth, head of the Institute for Applied Geosciences of the University of Darmstadt, to let us use the laboratory and facilities.
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