Abstract. The roles of groundwater flow in the hydrological cycle within the alpine area characterized by permafrost and/or seasonal frost are poorly known. This study explored the role of permafrost in controlling groundwater flow and the hydrological connections between glaciers in high mountains and rivers in the low piedmont plain with respect to hydraulic head, temperature, geochemical and isotopic data, at a representative catchment in the headwater region of the Heihe River, northeastern Qinghai-Tibet Plateau. The results show that the groundwater in the high mountains mainly occurred as suprapermafrost groundwater, while in the moraine and fluvioglacial deposits on the planation surfaces of higher hills, suprapermafrost, intrapermafrost and subpermafrost groundwater cooccurred. Glacier and snow meltwaters were transported from the high mountains to the plain through stream channels, slope surfaces, and supraand subpermafrost aquifers. Groundwater in the Quaternary aquifer in the piedmont plain was recharged by the lateral inflow from permafrost areas and the stream infiltration and was discharged as baseflow to the stream in the north. Groundwater maintained streamflow over the cold season and significantly contributed to the streamflow during the warm season. Two mechanisms were proposed to contribute to the seasonal variation of aquifer water-conduction capacity: (1) surface drainage through the stream channel during the warm period and (2) subsurface drainage to an artesian aquifer confined by stream icing and seasonal frost during the cold season.

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.

Understanding the heavy metal (HM) contamination in alpine mountain headwaters regions is important to maintaining the ecosystem stability of the basin. A total of 119 water samples and 104 sediment samples were collected along tributaries and the main course of Heihe River. The concentrations of eight heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) in water and sediment were measured to describe their spatial variability and to assess water quality. To identify the origins and pathways of HMs, anions, cations, and trace elements, as well as δD/δ18O stable isotopes in water samples were also measured. The results of water quality assessment suggested that tributaries were affected by local mining activity. Factor analysis in sediments showed that all HMs in sediments were inherited from the parent bedrock. Both natural weathering and mining contribute HMs. Cr and Ni were homologous with a source from the weathering of basic gabbro and serpentine at Yushigou. Mn appeared to be influenced more by artificial activities such as agriculture and grazing. Depending on the mining technique involved, two pathways for the release of HMs were distinguished in this area. For open-pit mining, mining promoted the release of HMs primarily via enhanced weathering. For underground mining, HMs might have contributed to greater acid mine discharge at high elevations due to the weak weathering processes. As the elevation decreases, precipitation increases, and a series of complex hydrological factor significantly affect leaching and runoff. The study results can be applied to improve water management efficiency.

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