A unified analysis of global riverine eDNA reveals common associations of fish biodiversity with drainage characteristics.

Freshwater biodiversity is declining at a pace that outstrips the capacity of existing monitoring approaches both in temporal and spatial dimensions, highlighting the urgent need for rapid and scalable assessment and attribution of biodiversity states and changes. Here we present a global assessment and unified analysis of riverine fish biodiversity using environmental DNA collected from 1,818 sites across 113 river systems spanning 5 continents. We quantified species richness, functional redundancy, phylogenetic diversity and genetic sequence diversity, and related them to drainage characteristics. Our results showed that environmental DNA effectively captured global patterns of multi-faceted riverine fish biodiversity and disentangled the roles of climate and different aspects of human activities in shaping biodiversity-area relationships. The accumulation of biodiversity with catchment area was consistently enhanced in warmer climates, while human activities weakened this scaling. Further, species richness, functional and genetic sequence diversity exhibited stronger negative responses to human activities in larger catchments. In contrast, phylogenetic diversity was negatively affected by human activities, yet this effect diminished as catchment area increased, highlighting the facet-dependent nature of biodiversity responses to environmental gradients and catchment characteristics. Our findings demonstrate the power of environmental-DNA-based datasets for harmonized, multi-faceted biodiversity assessments, offering a scalable approach for detecting and attributing biodiversity change and informing conservation strategies under accelerating global change.