DRY-SEASON WATER CHEMISTRY DOWNSTREAM OF THE WORD’S LARGEST TROPICAL GLACIER, COROPUNA, PERU

Over 70% of tropical glaciers in the world are found in the Andes Mountains of Peru and are important sources of drinking and agricultural water for millions of people. They provide a critical buffer from seasonally low or absent precipitation during the dry season from May-September. These tropical glaciers can have different meltwater chemistry than alpine glaciers due to tropical climate dynamics. A more complete understanding of water chemistry dynamics below tropical glaciers is needed as glacial recession threatens future dry-season water supplies and quality in these areas. To investigate water chemistry during the dry season, we collected 11 samples from streams and springs discharging from the Coropuna glacier in southern Peru, the most expansive tropical glacier in the world. The samples were analyzed for trace elements and stable isotopes. To examine the contribution of glacial melt vs meteorically recharged groundwater to local watersheds, a principle components analysis (PCA) was used with different sets of variables from the trace element, stable isotope, and probe parameter data taken at each sample site. The PCA was optimized by selecting the most relevant input parameters. Spatial variability in water chemistry was examined by comparing with local geology. Stable isotope results showed that different catchments have potentially high variability in their dependence on glacial melt versus local groundwater. PCA results showed differences in water chemistry between sampling sites that may be related to glacial ice melt, thermal groundwater, or local geology. This method shows early promise for being an effective tool in better understanding tropical glacier water chemistry dynamics and the implications for communities that rely on them.