Cheng Zhang, Ke Li, Qingqing Fang, Shanghong Zhang
To achieve a systematic and basin-wide assessment of Aquatic Ecological Health in the Yangtze River Basin, we developed an integrated assessment system based on multi-source data. The system synthesizes hydrological monitoring records, remote sensing products, long-term water quality observations, and literature-derived biological surveys to address data heterogeneity, extensive spatial coverage, and variability among water body types. By integrating long-term and spatially continuous datasets, the system captures longitudinal upstream–downstream gradients and the distinct ecological characteristics of rivers and lakes across the basin. Building on this data foundation, a hierarchical and multi-scale framework was constructed comprising three core dimensions: physical habitat, physicochemical properties, and biological condition. Indicator weights were determined using the Analytic Hierarchy Process (AHP), with consistency ratios (CR) below 0.1 to ensure reliability. To account for spatial heterogeneity among regions and water body types, benchmark values were derived through an integrated approach combining the reference condition method, generalized additive models (GAMs), the ASCETS method, and expert judgment, with parameters calibrated to local environmental conditions. Application to nine representative water bodies yielded an overall basin-wide ecological health score of 66.92, corresponding to a “Good” status. Upstream reaches generally exhibited higher ecological health than downstream reaches, and rivers performed better than lakes. In rivers, biological condition was identified as the primary limiting factor, whereas lakes were more strongly affected by eutrophication pressures. Overall, the assessment system balances scientific rigor with operational feasibility and provides a practical basis for ecological assessment and management in large river basins.