Abstract
AbstractWater 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. Here we use geochemical and isotopic values of water samples to evaluate relative contributions of melting glacier ice and groundwater to discharge in Bhutan. River water samples were collected between 3100 and 4500 m in the Chamkar Chhu (river) watershed of central Bhutan's Himalaya. Glacier ice and snow were sampled in the ablation zone of Thanagang glacier. Groundwater was parameterized from spring water at elevations of 3100 and 3600 m. Synoptic sampling was carried out in separate expeditions in July, August and late September 2014, to characterize monsoon and post-monsoon conditions. Results from a two-component hydrologic mixing model using isotopic and geochemical (sulphate) values show that the glacier outflow contributions decrease from ∼76% at 4500 m to 31% at 3100 m. A four-component hydrologic mixing model using end-member mixing analysis shows glacier ice melt increasing as a proportion of discharge over the 3 month sampling period, and consistently decreasing with distance downstream of Thanagang glacier terminus. These results indicate that isotopic and geochemical tracers can provide a quantitative evaluation of the source water contributions to streamflow in Bhutan.
Highlights
Bhutan is a country that is already at risk from a changing global climate (Meenawat and Sovacool, 2011)
We examined trends in oxygen isotopes with elevation for water samples collected in the Chamkar Chhu basin
Glacier outflow and ice do not fit as well as snow when considering the end members along the PC3 axis. These results suggest that the left side of the PC1 axis is unreacted water, the right side of the PC1 axis is reacted water, PC2 is driven by differences in potassium, and PC3 is driven by differences in d18O
Summary
Bhutan is a country that is already at risk from a changing global climate (Meenawat and Sovacool, 2011). Almost 70% of the population in Bhutan is directly or indirectly dependent on subsistence agriculture that is fed mostly by rivers originating from the glaciers and snow of the eastern Himalaya and by the abundance of monsoonal rainfall. A small and poorly developed country in the Himalaya, faces numerous vulnerabilities related to climate change, including landslides and flooding from melting glaciers, and impaired hydroelectricity generation (Meenawat and Sovacool, 2011). Bhutan lies in the eastern Himalaya, extending from 26°40’–28°15’ N to 88°45’–92°10’ E and covering an area of 38 394 km. The total area under snow/glaciers at maximum snow accumulation is 2989 km (7.5% of the total country area)
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