Using geochemical and isotopic chemistry to evaluate source water contributions to the hydrology of two high-elevation basins in the Himalayas of Nepal
Abstract
Water stored as ice and snow at high elevations is a resource that plays an important role in the hydrologic cycle, particularly in the timing and volume of downstream discharge. In order to gain a better understanding of the impacts of climate change on water resources, it is first necessary to improve the quantification of the origins of river discharge. The vulnerability of the cryosphere to increasing temperatures underscores the need for work on estimating the volumes of ice and snow that move down from mountains as melt water. Here we use geochemical and isotopic composition of water samples to evaluate relative contributions of different water sources to discharge in two high elevation basins of Nepal. River water samples collected between 1400 and 3745 meters in the Langtang Valley of central Nepal's Himalayan Mountains in May/June 2012 are compared to Langtang Valley samples collected in November/December 2008 to examine seasonal variations. The winter 2008 mixing model results are compared to the summer 2012 mixing model results. A decreasing trend with elevation of δ18O (more depleted) in river water was found. The range of δ18O and δ2H values found in the river and source waters, including glacier melt and groundwater, are also compared between the two years. In order to constrain the variability of South Asian monsoon rainwater chemistry, rain samples were collected along an elevational gradient in Nepal's Khumbu Valley, 120km east of the Langtang Valley, between 2660m and 5600m in June/July 2012. In addition to rain water, other end member and river water samples were collected to conduct a mixing model in the Khumbu Valley above the village of Pheriche. The unique geochemical and isotopic chemistry of the different source waters in both of these study areas may allow for confident estimation of glacier melt, snow melt, precipitation, and groundwater contributions to discharge.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMGC11A0963W
- Keywords:
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- 1022 GEOCHEMISTRY / Composition of the hydrosphere