Stream Functioning Across an Endorheic Basin in the Dry Andes

Water scarcity is a defining constraint for both ecosystem function and lithium resources development in the arid, high elevation region of the Puna Plateau in South America. Despite this, the processes that govern streamflow generation in the region remain poorly understood. This study aims to characterize streamflow dynamics in the Salar de Pastos Grandes watershed using an integrated approach drawing from physical, geochemical and remotely sensed hydrologic data. Weekly streamflow gauging served as the primary dataset which was supported by insights from environmental tracers, climate data and remotely sensed vegetation indices. Streamflow fluxes are modulated by topography, discrete precipitation events, temperature fluctuations and vegetation extents. Perennial streamflow is generated in catchments with significant area above 5000 meters above sea level. In contrast, ephemeral flows are responsive to precipitation and groundwater releases from bofedal wetlands. All basin waters were recharged >65 years ago and there is a gap in streamflow flux and modern precipitation inputs, indicating there is likely an additional source of relic water to streams. These findings inform a conceptual model for stream functioning in the dry Andes and these results have implications for freshwater availability studies and process-based groundwater models in this region.