China Water Resources

长江三峡工程及其上游梯级水库群的联合调度运行改变了中下游水沙输移过程，清水下泄与中游大型支流、湖泊的复合水动力作用共同重构了水体营养环境格局。基于2023—2024年完整水文周期的系统监测，揭示了湖北宜昌至江西九江河段泥沙特性、营养盐及溶解性有机质（DOM）的时空演变规律。结果表明：水库调度显著改变了泥沙组成特征，汛期泄洪过程导致粉粒占比急剧升高至95.2%，泥沙中值粒径呈现出3.2～59.5μm的空间分异，支流入汇对局部河段的黏粒富集具有显著贡献；水沙耦合作用对营养盐迁移转化具有选择性影响，极细泥沙显著增强了对磷的吸附能力，溶解态硅酸盐与泥沙含量呈显著正相关，而氮素分布主要受人类活动调控，与泥沙特性的相关性较弱；DOM组分表现出明显的季节演替特征，非汛期以微生物源腐殖酸为主，汛期则新增陆源黄腐酸和其他特征腐殖质，其组分数量从非汛期的2种增至汛期的4种。研究揭示了三峡工程体系调控下“水沙-营养盐-有机质”的协同变化特征，为长江中下游生态保护提供科学依据。

The joint regulation and operation of the Three Gorges Project and the cascade reservoirs upstream have altered the processes of water and sediment transport in the middle and lower reaches of the Yangtze River. The combined hydrodynamic effects of clear-water discharge and the inflows from major tributaries and lakes in the middle reaches have reshaped the nutrient environment pattern of the river. Based on systematic monitoring during the complete hydrological cycle from 2023 to 2024, this study reveals the spatiotemporal evolution of sediment characteristics, nutrients, and dissolved organic matter(DOM) in the river section from Yichang, Hubei to Jiujiang, Jiangxi. The results show that reservoir regulation significantly changed sediment composition characteristics. During flood discharge, the proportion of silt particles sharply increased to 95.2%, and the median sediment particle size exhibited spatial variation ranging from 3.2 to 59.5 μm. Tributary inflows made significant contributions to local clay enrichment. The coupling of water and sediment had selective effects on nutrient migration and transformation: very fine sediment markedly enhanced the adsorption capacity for phosphorus; dissolved silicate showed a significant positive correlation with sediment content; while nitrogen distribution was mainly controlled by human activities and showed a weak correlation with sediment characteristics. DOM components displayed clear seasonal succession characteristics, with microbial-derived humic acids dominating during the non-flood season, and additional terrestrial fulvic acids and other characteristic humic substances-emerging during the flood season, increasing the number of DOM components from 2 in the non-flood season to 4 in the flood season. The study elucidates the synergistic variation characteristics of the “water-sediment-nutrient-organic matter” system under the regulation of the Three Gorges Project system, providing a scientific basis for ecological protection in the middle and lower reaches of the Yangtze River.