Water and material cycles in rivers are controlled by diverse sources of recharge and flow paths, which exhibit spatial and temporal variations in the contributions of water sources and hydrologic processes. To assess the variation of water recharging, the stable isotope abundances of hydrogen and oxygen (δH and δO) of 152 water samples collected from the Yangtze River mainstream during May (the flat season) and September (the wet season) in 2021 were analyzed. Bayesian modelling was used to calculate the contribution rates of precipitation, glacier snow meltwater, and groundwater. The isotopic compositions of precipitation and the river exhibited comparable seasonal and spatial characteristics. The Bayesian model results showed that the mainstream was governed by precipitation, with a greater contribution of precipitation in the lower reaches during the wet season. Lakes had a larger contribution during the flat season, as evidenced by the greater increase in the magnitude of δO values in the mid-lower reaches during this period. The mid-lower reaches of the river had a decreased river evaporation line (REL) slope, which could be owe to lake replenishment. In addition to intensifying the seasonal variations in the contribution ratios of the lakes, the emplacement of the Three Gorges Dam (TGD) reduced the groundwater contribution of the reservoir. This study enhances our understanding of the hydrological and material cycles in the Yangtze River Basin and provides vital baseline knowledge on the contribution of different recharge sources in the mainstream.

中文翻译：

---

氢氧稳定同位素长江补给水量的季节和空间变化


河流中的水和物质循环受不同补给源和流动路径的控制，表现出水源和水文过程的贡献的空间和时间变化。为了评估补水变化，对2021年5月（平季）和9月（丰水期）从长江干流采集的152个水样的氢和氧（δH和δO）稳定同位素丰度进行了分析。采用贝叶斯模型计算降水、冰川雪融水和地下水的贡献率。降水和河流的同位素组成表现出类似的季节和空间特征。贝叶斯模型结果表明，干流受降水支配，雨季下游降水贡献较大。平季期间湖泊贡献较大，这一时期中下游δ18O值增幅较大。河流中下游河流蒸发线（REL）斜率减小，这可能是由于湖泊补给所致。三峡大坝的修建除了加剧了湖泊贡献率的季节变化外，还减少了水库对地下水的贡献。这项研究增强了我们对长江流域水文和物质循环的了解，并为主流不同补给源的贡献提供了重要的基线知识。