Date of Award

Spring 2-12-2015

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Geography

First Advisor

Mark W. Williams

Second Advisor

Richard Armstrong

Third Advisor

Peter Blanken

Abstract

While there have been increased efforts recently to understand the dynamics of Asia’s cryosphere, glacier melt dynamics and hydrograph separation of river discharge are open questions. A multi-year, multi-seasonal data set of water chemistry from the Langtang Valley, Nepal is used to explore source waters and flow paths that contribute to Langtang River discharge. Bulk monsoon precipitation samples from the Langtang Valley shows a linear relationship of 2.3‰ depletion of the oxygen-18 isotope per kilometer of elevation gain. Differences in hydrochemistry of samples from the clean-ice Khimsung Glacier and debris-covered Lirung Glacier suggest that debris-cover can induce more melt-freeze cycles in glacier ice and can elevate the concentrations of geochemical weathering products in glacier outflow. Additional data shows seasonal transitions in the composition of Langtang River discharge Two-component mixing models using melt water and groundwater oxygen-18 values are sufficient to explain October 2008 and November 2013 Langtang River water samples, but a combination of rain/snow and melt water oxygen-18 isotope values are required to explain May 2012 Langtang River water samples. End Member Mixing Analysis (EMMA) using geochemical and isotopic tracers suggests reacted meltwater contributes the majority of flow in late fall, while the proportion of unreacted meltwater increases during the late spring and early fall – the shoulder seasons of the monsoon. We hypothesize our data set is missing characteristic monsoon water and utilize a late May Langtang River water sample as a proxy for monsoon-influenced groundwater in the EMMA. Results offer insight into the plausibility of flow sources and pathways in the basin.

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