Natural and human contributions to pre-monsoon snow and stream chemistry in the Khumbu/Mt. Everest region, Nepal

Here we present the most comprehensive study thus far of the chemical composition of surface snow, streams, and ice in the Khumbu region, with measurements of major and trace elements, rare earth elements, major ions, black carbon, and stable isotopes. Altogether, from the Khumbu region we collected 94 snow samples, 18 stream samples and 200 samples from 1.7m of ice, drilled from the Khumbu Glacier and dated to the pre-modern era using ¹⁴C dating. Based on our results, we find dust originating from western sources dominated the pre-monsoon aerosol deposition. Less often, aerosols were transported from southerly air mass sources and deposited in the Khumbu, as represented in this study by Cyclone Fani, a precipitation event that occurred on May 3-4, 2019, coinciding with field sampling. We detect anthropogenic chemical fingerprints (e.g., Pb, Bi, Cs, and black carbon) throughout the Khumbu region in surface snow and/or stream chemistry, indicating local and/or long-range transport of polluting atmospheric aerosols. While our study does not identify the distinction between local and distal sources of contaminants, these initial findings have wide reaching implications for the potable water for residents and visitors of the Khumbu region, and populations further downstream. Rising tourism in the Khumbu region will likely contribute to increased pollutant loading. This preliminary study reveals the necessity for more temporally and spatially extensive monitoring to determine anthropogenic impacts on the water system in the region.