Globally unified analysis of riverine eDNA reveals common associations of fish biodiversity with drainage characteristics

Freshwater biodiversity is declining at a pace that far outstrips the capacity of existing monitoring approaches to provide timely or spatially comprehensive assessments. This mismatch between the speed of ecological change and the resolution of traditional survey methods underscores an urgent need for rapid, scalable, and reliable tools to evaluate biodiversity states and attribute observed changes to environmental drivers. In this context, environmental DNA (eDNA) has emerged as a promising alternative, as it enables broad biodiversity detection with minimal sampling effort. However, despite its potential, global-scale and multi-faceted evaluations remain rare. Here, we present one of the first worldwide assessments and unified analyses of riverine fish biodiversity based on eDNA samples collected from 1,818 sites across 113 major river systems. We quantified four complementary dimensions of biodiversity—species richness, functional redundancy, phylogenetic diversity, and genetic sequence diversity—and examined how each dimension relates to fundamental drainage characteristics and environmental gradients. Our analyses revealed that eDNA not only captured global biogeographic and ecological patterns with remarkable consistency but also enabled us to disentangle the relative contributions of climate and human activities in shaping biodiversity–area relationships. Catchments situated in warmer climates exhibited consistently steeper biodiversity accumulation with increasing area, whereas intensified human activities markedly dampened this scaling effect, pointing toward widespread anthropogenic erosion of freshwater ecosystems. Interestingly, different biodiversity facets displayed distinct sensitivities to human pressures. Species richness, functional diversity, and genetic sequence diversity all showed stronger negative responses to anthropogenic disturbance in larger catchments, suggesting cumulative impacts that amplify across spatial scales. In contrast, phylogenetic diversity experienced its most severe declines in smaller catchments, with the magnitude of these impacts diminishing as catchment size increased. This facet-dependent pattern highlights the complex, non-uniform, and scale-specific nature of biodiversity responses to environmental change. Overall, our findings demonstrate the power of large-scale eDNA datasets for harmonized, multi-dimensional biodiversity assessments. They provide a scalable and integrative pathway for detecting and attributing biodiversity change, ultimately delivering essential insights to inform targeted conservation strategies and guide freshwater ecosystem management under accelerating global environmental change.