Using Isotopic and Geochemical Tracers to Determine the Contribution of Glacier-Snow Meltwater to Streamflow in a Partly Glacierized Alpine-Gorge Catchment in Northeastern Qinghai-Tibet Plateau

摘要

Compared with arctic and subarctic catchments, our knowledge about the hydrological functions of glaciers and porous aquifers is still limited for the partly glacierized alpine-gorge headwaters in the Qinghai-Tibet Plateau. Here we examine the impact of glacial and groundwater storage on the variability of warm-season (June to September) discharge from the Hulugou catchment, an alpine-gorge headwater with 3% glacial coverage, by quantifying the timing and magnitude of contributions of glacier-snow meltwater, baseflow, and rainwater to streamflow using a three-component hydrograph separation model. It is found that baseflow was the largest component (55 ± 2%) of warm-season streamflow while glacier-snow meltwater also contributed significantly (30 ± 10%) despite of the very low glacial coverage. We suggest that the water flowing out of glaciers was mainly supplied by the melting short- and intermediate-term storages (i.e., snow over glaciers), which led to the high meltwater contribution to streams during the warm season and the high peaks of meltwater discharge following heavy precipitation events. The porous aquifers in piedmont plain may serve as major reservoirs that store a growing body of groundwater during the warm season, which explains the general increasing trend of baseflow contribution during this period. The moraine and talus deposits in high mountains, by contrast, allow groundwater to pass through them quickly and therefore being responsible for the obvious responses of baseflow contribution amount to heavy rainfall events. Our findings suggest that small mountain glaciers and porous aquifers may play a greater role than expected in hydrological regulation in the alpine-gorge catchments of northeastern Qinghai-Tibet Plateau.