Integrating functional connectivity and habitat stability into fish habitat assessment and optimizing ecological operation

With the development of society and the growing demand for an energy transition, the scale and installed capacity of hydropower have been steadily increasing. However, this has led to a series of ecological and environmental issues, with threats to fish habitats caused by hydrological alterations being particularly significant. Habitat assessment can be used to effectively identify the impacts of hydraulic projects on ecosystems, particularly with respect to ecological flows and ecohydrological characteristics. The current methods of ecological flow determination focus solely on habitat area while overlooking habitat connectivity. Additionally, the identification of ecohydrological characteristics is based entirely on hydrological data, neglecting habitat stability. We selected the large national spawning ground downstream of the Xiangjiaba (XJB) hydropower station and the protected fish species Myxocyprinus asiaticus (M. asiaticus) as research subjects and incorporated functional connectivity and habitat stability into a fish habitat assessment model. Functional connectivity of habitat patches was evaluated using circuit theory, and habitat stability under flow variations was assessed through overlap rate. By simulating the habitat distribution and variations under various flow scenarios, we identified the suitable ecological flow range as 2205–2695 m³/s. The optimal daily flow variation range was determined to be -41.8 to 53.1 m³/s, with the extreme range of -137.3 to 171.8 m³/s. On the basis of these habitat requirements, we proposed an optimized ecological operation scheme. Compared with actual operations, in the minimum ecological deviation scenario, power generation is reduced by only 0.44 %, and the degree of ecological flow deviation is considerably decreased by 43.47 %. Moreover, the optimized scheme yields a stable and suitable flow lasting for one month, which is conducive to promoting the spawning and reproduction of M. asiaticus. The findings and framework presented in this study provide valuable guidance for reservoir management and assessments of watershed ecology.