Spatio-seasonal characteristics and controlling factors of surface water stable isotope values (δ18O and δD) across the Inner Mongolia Reaches of the Yellow River Basin, China: Implication for hydrological cycle

Inner Mongolia Reaches of the Yellow River Basin (IMR-YRB) in China, knwon as the "Jiziwan" economic belt. High spatio-seasonal resolution sampling data of the surface waters in the IMR-YRB were applied (189 samples collected from 63 sites during the wet (July 2021), dry (October 2021) and normal (April 2022) seasons). The testing results of stable H and O isotopes were combined with backward wind trajectory modeling and geostatistical analysis to identify the spatio-seasonal characteristics of the surface water cycle and its controlling factors. The results showed that surface waters were mainly recharged by precipitation from summer monsoon, resulting in depleted isotopic contents (low δ18O and high d-excess) during the wet season. In contrast, most of the surface waters were characterized by isotopic enrichment (high δ18O and low d-excess) during the dry and normal seasons, which was attributed to the effects of continuous evaporation. In addition, there were some samples that exhibited isotopic depletion during the dry and normal seasons due to the effects of groundwater discharge or snowmelt recharge. Overall, this study improved the understanding of the surface water cycle at a large-scale basin for understanding hydrologic processes in other regions.