Water and Soil Chemistry Interactions in the Khumbu Valley, Nepal

Abstract:

Climate change and retreating Himalayan glaciers have raised questions about water security in Himalayan countries. These changes in drivers may also affect water quality. Here we evaluate the possible impact of climate change on local water quality of the Dudh Koshi basin in the Khumbu Valley region of Nepal, with an emphasis on snow and ice melt interactions with underlying soils. Precipitation, river water, and soils were sampled in 2012-2014, from the Lukla area (2800 m) to above the Pyramid International Laboratory (5,000 m). Here we focus on presenting results for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate, and stable water isotopes. The spatial and temporal variability of the surface water chemistry is compared to ratios of carbon to nitrogen in soil samples. Soil carbon to nitrogen ratios decrease with elevation, consistent with dilution in surface water chemistry. Stable water isotopes show large changes with season and elevation. Summer rains are generally 15-20 parts per mil more enriched than winter snow in O18, while values become more depleted by about 10 parts per mil with increasing elevation. In contrast, water samples show much less variation by season and elevation. The trends explored are representative of the influence of both debris-covered glacier outflow of the upper valley and biogeochemical processes on the water and soil.