Methodological divergence in river health assessment: A comparative study of integrated assessment versus multi-taxon IBI

Different approaches to river health assessment may yield contrasting evaluation outcomes; however, their applicability under varying disturbance regimes remains insufficiently understood. Using the Chishui River as a case study, the performance of an integrated assessment approach was compared with that of the Phytoplankton Index of Biotic Integrity (P-IBI), Zooplankton Index of Biotic Integrity ( Z -IBI), and Benthic Macroinvertebrate Index of Biotic Integrity (B-IBI). Environmental drivers underlying differences among assessment outcomes were also examined. The integrated assessment approach and B-IBI consistently indicated better ecological health in the upstream and midstream reaches than in the downstream reach, as well as higher ecological health during the dry season than during the wet season. In contrast, P-IBI and Z -IBI generally assigned higher health grades to downstream reaches and wet-season conditions. Analyses of environmental drivers revealed distinct responses of biological assemblages to nutrient enrichment and associated environmental gradients. Consequently, different assessment approaches reflected different ecological responses to environmental stressors and varied in their applicability across disturbance gradients. Overall, B-IBI showed a high level of concordance with the integrated assessment approach and was better suited to evaluating river health in heavily disturbed reaches. In contrast, plankton-based IBIs appeared more suitable for rapid ecological assessments in relatively undisturbed river systems. Based on these findings, a disturbance-based framework for selecting river health assessment approaches was proposed, providing a scientific basis for river health evaluation and watershed management decision-making. • Different river health assessment approaches showed contrasting ecological outcomes. • Biological assemblages exhibited distinct responses to nutrient enrichment gradients. • B-IBI showed high concordance with integrated assessment in disturbed reaches. • A disturbance-based framework was developed for selecting assessment approaches.