Ecological flow evaluation method based on Habitat Diversity Index --An empirical study from the upper Yalong River in China.

Traditional ecological flow calculations often rely on species-specific habitat preferences, but this approach may adversely affect biodiversity conservation. This study proposes an innovative approach focused on habitat diversity, utilizing the Habitat Diversity Index (HDI) to evaluate ecological flows for benthic macroinvertebrate communities. By integrating fields surveys, hydrodynamic modeling, and biodiversity metrics, the study quantified habitat diversity through 24 distinct habitat types (combinations of water depth: 0-0.8m; flow velocity:0-2m·s) and analyzed its relationship with species richness. Key findings include: (1) the optimal conditions for dominant species were identified as water depth of 0.2-0.4 m and flow velocity of 0.4-0.7 m s; (2) HDI showed a strong positive correlation with species richness (Pearson's r = 0.70), confirming that higher habitat diversity supports greater biodiversity; (3) Generalized Additive Model (GAM) analysis revealed non-linear effects of flow velocity on macroinvertebrate density, with peak density observed at approximately 1 m s. The HDI-based approach identified an ecological flow of around 100 m s, balancing habitat diversity and community density, which outperformed traditional species-centric methods. This study advances river ecosystem management by prioritizing habitat heterogeneity, offering a scalable framework for biodiversity conservation in regulated rivers. Practical implications for setting ecological flows and mitigating the impacts of hydropower are also discussed, highlighting the need to integrate multi-species habitat requirements into adaptive management strategies.