Insights into moisture sources and evolution from groundwater isotopes (2H, 18O, and 14C) in Northeastern Qaidam Basin, Northeast Tibetan Plateau, China

Knowledge of moisture sources is of great significance for the understanding of groundwater recharge and hydrological cycle. However, it is often difficult to identify the moisture sources and evolution especially in the areas with complex cli-mate system. Isotopes in groundwater that acts as a climate archive provide a unique perspective on the moisture sources and evolution. In this study, the stable isotopes (2H, 18O) of precipitation and groundwater, radioactive isotope (14C) of groundwater, water vapor trajectory modeling (HYSPLIT models) and d-excess based on mass balance model were em-ployed to reveal the groundwater origin, moisture source and evolution in the northeastern Qaidam Basin, northeast Tibetan Plateau, China. The stable isotopic compositions indicate that the precipitation in the mountainous areas is the main origin of groundwater. The spatiotemporal variation of groundwater d-excess together with HYSPLIT modeling suggest that the moisture sources in the northeastern Qaidam Basin have been controlled by the Westerlies and did not alter obviously with time, whereas Delingha with relatively low elevation is influenced by both the Westerlies and local recycled moisture. More than 80 % water vapor derives from the northwest of study area for the plain and mountainous area, except for the mountainous area of Delingha, where approximately 23 % water vapor originates from the surface water evaporation in the plain area. The water vapor with high d-excess formed in the plain area is transported to the mountainous area and mixed with advected water vapor, resulting in the large d-excess of groundwater in Delingha. The moisture recycling frac-tion in precipitation for the mountainous area of Delingha is estimated to be about 2.0 % by using d-excess-based mass bal-ance model. The results of the study could be helpful to the understanding of hydrological cycle of the area and elsewhere.