The response of chemical weathering to climate could be examined in a way by investigating seasonal changes in river geochemistry. Here, we determined the major elements, δC of DIC, Sr/Sr, δLi, and δMg of monthly time-series water samples at the Daojieba Hydrological Station in lower reach of the Nujiang River over a hydrological year. During high-flow seasons, the dissolved Sr/Sr, δLi, and δMg exhibit comparatively high values. Sr/Sr ratio, together with δC of DIC, Si/Ca ratio, and pH value of river water, indicate an enhanced silicate weathering contribution to river dissolved load, and river δLi is impacted by secondary mineral formation-related fractionation during these periods. Similar to the Sr/Sr ratio, δMg of river water is indicative of a dominant source control. The positive relationship between Mg/Na ratio and δMg value suggests that the prior weathering of Mg-rich silicate minerals could be important for elevated δMg and Mg/Na molar ratio during high-flow seasons, while the Mg isotope fractionation signal can be seen when runoff increases dramatically. During low-flow seasons, river Sr/Sr and δMg values evolve to a carbonate weathering signal, whereas river δLi reflects a more congruent silicate weathering, and these changes point to the obvious influence of geothermal water in these periods. The covariations of δLi, δMg, and discharge are observed. Changes in runoff can significantly impact the isotopic composition of Li and Mg by changing the hydrological flow path, in which dominant reactions of mineral dissolution and secondary mineral formation vary. This study highlights the hydrological control on Li and Mg isotopic compositions of the Nujiang River water, which could be considered the dominant control of monsoon climate on weathering processes in high-relief river basins at a short-term scale.

中文翻译：

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道界坝水文站怒江水锂、镁同位素组成的季节变化：对化学风化的影响


化学风化对气候的响应可以通过研究河流地球化学的季节性变化来检查。本文对怒江下游道界坝水文站一个水文年的月时间序列水样的主要元素DIC、Sr/Sr、δLi和δMg进行了测定。在丰水季节，溶解的Sr/Sr、δLi和δMg表现出较高的值。 Sr/Sr 比值，连同 DIC δ13C、Si/Ca 比值和河水 pH 值，表明硅酸盐风化对河流溶解负荷的贡献增强，并且河流 δLi 在此期间受到与次生矿物形成相关的分馏的影响。与 Sr/Sr 比率类似，河水的 δMg 表明主要源头控制。 Mg/Na 比值与 δMg 值之间的正相关关系表明，富镁硅酸盐矿物的前期风化对于高流量季节 δMg 和 Mg/Na 摩尔比升高可能很重要，而当径流急剧增加。在枯水季节，河流Sr/Sr和δMg值演化为碳酸盐风化信号，而河流δLi则反映了更一致的硅酸盐风化信号，这些变化表明地热水在这些时期的影响明显。观察到 δLi、δMg 和放电的协变。径流的变化可以通过改变水文流动路径来显着影响锂和镁的同位素组成，其中矿物溶解和次生矿物形成的主要反应发生变化。 本研究强调了水文对怒江水锂和镁同位素组成的控制，这可以被认为是季风气候在短期尺度上对高地形河流流域风化过程的主导控制。