Seasonal glacial meltwater contributions to surface water in the Bolivian Andes: A case study using environmental tracers

Study region The Cordoriri watershed and vicinity in the Cordillera Real, Bolivia, South America Study focus Recent warming has contributed to substantial reductions in glaciers in many regions around the globe. Melting of these glaciers alters the timing and magnitude of streamflows and diminishes water resources accumulated in past climates. These changes are especially acute in regions with small glaciers and problematic for populations relying on surface water. In Bolivia, most glaciers are less than 0.5 km² and about 2 million people draw water in part from glacier-fed watersheds. Sparse monitoring, however, has limited estimates of glacial meltwater contributions. The use of environmental tracers is one approach that can quantify the contributions of glaciers. We present isotopic and anion data for streams, reservoirs, arroyos, precipitation, and glaciers for the wet and dry seasons in 2010, 2011, and 2012. New hydrological insights for the region Glacier meltwater data shows distinct seasonal isotopic values, presenting opportunities for end-member mixing analyses. From isotopes, we estimate 31–65% of the water measured in high altitude streams and reservoirs during the 2011 wet season originated from melting of ice and recent snow, while glacier ice contributed 39–71% of the water in reservoirs in the 2012 dry season. This study demonstrates that more comprehensive sampling in the region could quantify the contributions of glacial meltwater and nonglacial sources to surface water supplies.