Triple isotopes (δD, δ18O, δ17O) characteristic of river water and groundwater in an arid watershed from Qaidam Basin, Northwestern China: implications for hydrological cycle

Combining traditional stable isotopes (δD and δ18O) and triple oxygen isotope (δ17O) is conducive to trace hydrological cycle processes. The application of triple oxygen isotopes primarily focuses on precipitation, which is lacking in river water and groundwater. In this study, the spatial variation of δD, δ18O, δ17O, d-excess and 17O-excess of river water and groundwater in Golmud River basin as well as the correlation between them were investigated to elucidate water origin and assess the evaporation influence on water bodies during flood season. Spatial changes in δD, δ18O and δ17O of river water exhibit a decrease-increase-stability pattern contrary to that observed for d-excess, 17O-excess has no distinct trend but is higher at both the source region and downstream areas. The results show that river water and groundwater originate from precipitation within the mountainous area, and the meltwater in the source region also contribute to the river water with high d-excess and 17O-excess during flood season. The combination of d-excess and 17O-excess reveal that river water is also affected by evaporation and mixing of river water in tributaries. It was found that the river water is recharged in the mountain area, undergoes evaporation in the upstream and leaks into groundwater in the midstream, which is recharged by the groundwater and evaporated again in the downstream. This study could provide a more comprehensive understanding of the potential and value of triple oxygen isotopes in the hydrological cycle.