Regional zooplankton community differences inform freshwater-organism water quality criteria refinement: an eDNA-guided framework.

National water quality criteria (WQC) for freshwater organisms are commonly derived from standardized toxicity datasets, but they rarely account for regional differences in biological communities and taxon sensitivity. Here, we used environmental DNA (eDNA) metabarcoding to characterize zooplankton communities at 30 surface-water sampling sites across four geographically and hydroclimatically contrasting regions of China. eDNA was used to provide taxonomic and community-level information, and regional representative taxon selection was followed by WQC refinement using independently compiled toxicity evidence. Regional grouping explained 33.52% of community compositional variation (PERMANOVA, R2 = 0.3352, P = 0.001), and measured water-quality variables were associated with regional assemblage differences. Combining spatial persistence, read-based regional enrichment, and network-topology metrics yielded 9, 9, 4, and 7 regional representative taxa for Kunming, Beijing, Ningbo, and Yinchuan, respectively. In the primary analysis, refined WQC were higher than the common national reference for Cu, Cd, and carbaryl and lower for Zn across all four regions, whereas Cr(VI), Pb, pentachlorophenol, and chlorpyrifos showed mixed regional patterns. Regional refinement also changed RQ-based risk characterization. Together, these results show that eDNA-guided representative-taxon selection can translate regional community differences into freshwater-organism WQC refinement and risk prioritization.