Spatial variation of water stable isotopes of multiple rivers in southeastern Qaidam Basin, northeast Qinghai-Tibetan Plateau: Insights into hydrologic cycle

River contains plenty of information on hydrological cycle. The water stable isotope approach is a powerful tool to unravel the hydrological processes such as river water sources, evaporation and river water-groundwater interaction. However, the spatial variation and influencing factors of stable isotope compositions in multiple rivers within a large basin and their indication to hydrological cycle have been less documented. This work reports on the spatial variation of stable water isotopic compositions of river water of four rivers and the underlying hydrological processes in the southeastern Qaidam Basin, northeast Qinghai-Tibetan Plateau, China. The results showed that the δD and δ18O values of individual river vary along the river flow directions (generally from south to north), and that of multiple rivers also exhibit an obvious spatial variation, which is mainly influenced by evaporation, groundwater discharge, moisture source and transport pattern and local precipitation. As for an individual river, the δD and δ18O of river water are gradually enriched by evaporation along the river flow direction, which are rapidly depleted due to groundwater discharge into river in the groundwater overflow zone. For multiple rivers, the stable isotopic compositions of river water are gradually depleted from the west to the east of the study area (i.e. approximately perpendicular to rivers’ flow directions), which are mainly controlled by moisture source and transport pattern. This study helps to enhance our understanding of the hydrological cycle in a large basin through combined analysis of water stable isotopic data from individual river and multiple rivers. The data evaluation methods and results of this study could be useful in other areas to understand hydrological processes and moisture transport pattern.