Triple isotopes (δD, δO, δO) 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 δO) and triple oxygen isotope (δO) is conducive to tracing 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 variations of δD, δO, δO, d-excess and O-excess of river water and groundwater in the 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, δO and δO of river water exhibit a decrease-increase-stability pattern contrary to that observed for d-excess, O-excess has no distinct trend but is higher at both the source and downstream regions. The results show that river water and groundwater originate from precipitation in the mountainous area, and the meltwater in the source region also contribute to the river water with high d-excess and O-excess during flood season. The combination of d-excess and O-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 mountains, undergoes evaporation in the upstream region and leaks into groundwater in the midstream region, which is recharged by the groundwater and evaporated again in the downstream region. This study could provide a more comprehensive understanding of the potential and value of triple oxygen isotopes in the hydrological cycle.