Assembly mechanism of zooplankton communities during the initial stage of the Yangtze-to-Huaihe water diversion project

While inter-basin water diversion is an important measure for optimizing water resource allocation and improving regional ecological health and can mitigate certain water quality issues, it can also trigger a series of complex ecological effects, particularly on zooplankton communities. This study focuses on Caizi Lake, the only storage lake along the Yangtze-to-Huaihe Water Diversion Project within the Yangtze River Basin, to systematically investigate the composition, diversity, and potential community assembly mechanisms of zooplankton during the early stage of engineering disturbances. The results indicate that disturbances induced by the water diversion project caused drastic changes in the aquatic environment, leading to a decline in zooplankton species diversity. Before hydrological connectivity, the community was primarily regulated by total nitrogen and water temperature, After connectivity, the dominant drivers shifted to dissolved oxygen, Secchi depth, and pH. Community assembly analysis revealed that during peak disturbance assembly signals were elusive, largely classified as undominated processes and accompanied by a rise in homogenizing dispersal, whereas in the recovery phase heterogeneous selection steadily increased. Overall, zooplankton communities exhibited significant responses to the hydrological connectivity of the water diversion project. This study enhances our understanding of the adaptive characteristics and assembly mechanisms of zooplankton communities under water diversion disturbances, while also suggesting some adaptive management strategies to support ecosystem resilience. • Water diversion disturbances reduce zooplankton diversity. • Zooplankton drivers shift from total nitrogen and water temperature to dissolved oxygen, transparency, and pH. • Water diversion enhanced undominated processes and homogenizing dispersal; heterogeneous selection increased in recovery.