Weirs are often constructed on mountainous rivers because of their low construction costs and their ability to provide irrigation and facilitate landscaping, yet there is little research on how fish habitat quality in mountainous rivers responds to weir distribution. This study categorized the distribution characteristics of weirs on typical reaches according to their sinuosity and calculated the corresponding habitat suitability index (HSI) and weighted usable area (WUA) under various discharge conditions using a coupled MIKE21 and habitat suitability model. Then, the relationship between the distribution characteristics of weirs and the quality of fish habitats under different discharge conditions was analyzed. The results show that weirs in mountainous rivers can affect the habitat suitability of the rivers, but this effect is closely related to discharge conditions and layout mainly because the key hydraulic factors that determine habitat quality for different sinuous reaches vary under different discharge conditions. This study found that in high-sinuosity rivers with high discharge conditions, water depth is the key factor determining the quality of fish habitats, so weirs can improve habitat quality by improving the suitability of downstream water depth. However, in other conditions, velocity is the key factor determining habitat quality, in which case weirs cannot improve habitat quality and can even degrade it. Therefore, other methods of improving velocity are needed to enhance habitat quality. The results of this study provide a reference for the protection of fish habitats in mountainous river channels and the determination of suitable locations for weir construction.

To clarify the mechanism by which reservoir thermal stratification influences the succession of zooplankton functional groups, this paper systematically reviews the national and international research progress and future development trends concerning both reservoir thermal stratification and zooplankton functional groups. Drawing on a systematic literature review and the theory of Self-organised Criticality (SOC), it proposes a novel quantitative research framework and explicates the logical chain through which the dynamic process of thermal stratification drives habitat differentiation, reorganises the topological structure of zooplankton functional-group interaction networks and consequently directs the community towards a self-organised critical state. The paper identifies the key scientific question that urgently requires resolution in this field as “How does the reservoir thermal stratification process drive zooplankton functional groups towards a self-organised critical state?” In response, three research priorities are established: (1) the driving effect of reservoir thermal stratification on zooplankton habitat differentiation; (2) the effect of habitat differentiation on the topological structure of zooplankton functional-group interaction networks; (3) the role of zooplankton functional-group interaction networks in determining the probability of occurrence of SOC states. It is worth emphasising that the SOC state is here construed as a probabilistic rather than an inevitable condition, contingent upon site-specific environmental circumstances. This research may offer scientific support for refining the theoretical framework of reservoir ecology and for strengthening adaptive reservoir management under extreme high-temperature conditions.