Meltwater Variation Influences High Alpine Water Quality in the Gokyo Valley, Nepal

Changes in seasonal and annual water contributions from melting snow and ice influence high alpine watershed hydrology across High Asia, however limited attention has been given to the resulting influence on water quality. To investigate the influence of snow and ice melt variation on water quality, samples were collected in the winter dry season in 2012 and 2016 from tributary streams, which serve as local drinking water sources and contribute to the Dudh Koshi watershed in the Gokyo Valley, which is located in the Khumbu Region of Nepal. Samples were collected along a transect from Lukla (2798 m) to Gokyo (4742 m) and at a confluence on the Dudh Koshi river, which is a major tributary to the Sapta Koshi River, and ultimately the Ganges River. Water samples were analyzed for E.coli, an indicator bacteria of fecal contamination, along with dissolved organic carbon (DOC), total dissolved nitrogen (TDN), arsenic, and oxygen isotopes to explore hydrologic un-mixing of source contributions. Water chemistry results were then compared to results of MODIS-derived remote sensing products to separately calculate daily melt outputs from snow and glacier ice, within the nested watershed basins where each sample was collected, along tributary streams and at the downstream Dudh Koshi confluence. An automated partitioning method generates maps of: 1) snow over glacier ice, 2) exposed glacier ice, and 3) snow over land, which are inputs to a temperature index (TI) model that yield melt water volumes contributing to stream flow. We found that the variation in annual contributions of melt from snow and ice may influence the local water quality. High flow years may lead to more contamination of surface drinking water with wastewater, based on field measurements of E. coli, and low flow years may lead to higher concentrations of naturally occurring elements, such as Arsenic, due to less dilution. Understanding these scenarios, which have consequences for human health, is important for long-term adaptation strategies to a changing climate, due to the changes in snow and ice melt contributions.