Long‐Time Sequence Data Revealed the Pattern of River Habitat Evolution and Its Effect on River Organisms in the Three Gorges Reservoir‐Controlled Jingjiang River

ABSTRACT Globally, the operation of hydraulic engineering projects alters downstream river habitat, thereby affecting aquatic organisms and threatening aquatic ecosystems. Using 30 years of time series data and statistical analyses, including structural equation modelling (SEM) and redundancy analysis (RDA), this study examined the influence of the world's largest reservoir—Three Gorges Reservoir (TGR)—on the habitat and organisms of the downstream Jingjiang River. Among all habitat components, water and sediment are the most fundamental. After reservoir operation, the proportion of flood‐season discharge in the annual total decreased by about 5%, while suspended sediment concentration sharply declined from about 0.8 kg/m 3 to less than 0.2 kg/m 3 . Water and sediment discharge determine other components of river habitat: changes in discharge increased water temperature, while reduced sediment supply intensified channel scouring and lowered water levels. They also shape the chemical habitat by controlling nutrient fluxes and composition. Water discharge directly affects fish spawning through changes in flow magnitude and timing, while sediment indirectly affects spawning by modifying water transparency and nutrient availability. Variations in water and sediment together explained approximately one‐third of the observed changes in fish spawning. Although reservoirs alter downstream habitats, they also offer opportunities for habitat restoration and organism protection through ecological scheduling, which may even be more effective than managing individual habitat components at local scales.