Impacts of ecological water supplement projects on fish habitat suitability in a high-leakage river in China

Ecological water supplement projects (EWSP) aimed at restoring damaged river ecosystems can change river hydrological processes, and loss of water through river leakage can potentially affect the spatiotemporal differences of river hydraulic factors, thus further affecting the habitat suitability of aquatic organisms. Therefore, assessing the impact of EWSP on habitats, considering leakage, is critical for high-leakage rivers recharging underlying and adjacent groundwater. In this study, a river habitat suitability simulation framework was established based on the surface water and groundwater coupling model and a fuzzy logic model. This frame-work was implemented to simulate the habitat suitability of a high-leakage reach of the Yongding River in China under different scenarios. The results showed that neglecting leakage would lead to overestimation of fish habitat suitability. The impacts of EWSP on the habitat were positive in spring; however, it was the opposite in autumn, which was affected by factors that led to spatiotemporal differences in leakage, such as topography and geology, water supplement season, and magnitude and duration of discharge. The optimal water supplement discharge of the Yongding River was 15-25 m3/s, which is consistent with the optimal discharge range recommended by the Tennant method. In the future, with the gradual decrease in leakage, habitat suitability will continue to improve, and the water quantity of EWSP required to maintain the same degree of weighted usable area will continue to decrease.