Reservoirs are well known as a far-reaching human modification on the functions of natural river networks. However, changes in the chemistry and reactivity of dissolved organic matter (DOM) responding to hydrological management for water retention structures, and its influence on the river carbon cycle, remain poorly understood. Here we show that hydrological management does shape the molecular composition of DOM in the world's largest Three Gorges Reservoir, as revealed by optical spectroscopy and ultrahigh-resolution mass spectrometry. Relatively higher terrestrial input, molecular complexity, isomeric complexity, and environmental stability of DOM were observed during the storage period, whereas the inverse occurred during the drainage period. The results demonstrate that the hydrodynamic processes, which are mainly controlled by water intrusion from mainstream to tributaries, are likely the underlying mechanism controlling DOM chemistry. Integrated with observations from worldwide river reservoirs, the DOM degradation experiments suggest that reservoir hydrological management would enhance DOM mineralization, thereby increase CO₂ emission and change the river carbon cycle.

水库是人类对天然河网功能的深远影响而闻名。然而，对保留结构的水文管理响应的溶解有机物（DOM）的化学和反应性变化及其对河流碳循环的影响仍然知之甚少。在这里，我们证明了水文管理确实影响了世界上最大的三峡水库中DOM的分子组成，如光谱学和超高分辨率质谱分析所揭示的那样。在储存期间观察到相对较高的陆地输入，分子复杂性，异构体复杂性和DOM的环境稳定性，而在排水期间则相反。结果表明，流体动力学过程 它们主要是由从主流到支流的水入侵控制的，可能是控制DOM化学的潜在机制。结合全球河流水库的观测资料，DOM降解实验表明，水库水文管理将增强DOM矿化作用，从而增加CO₂排放和改变河流碳循环。