Effect of Nutrient Enrichment on Alpha and Beta Diversity of Macroinvertebrate Community in a Boreal River of Northern China

Nutrient enrichment poses a major threat to freshwater ecosystems, yet integrated assessments of its effects on multiple dimensions of biodiversity remain limited. In this study, we investigated the responses of taxonomic, functional, and phylogenetic diversity (alpha and beta) of macroinvertebrate communities along a nutrient gradient in the Taizi River, a boreal river in northern China. The results revealed that macroinvertebrate abundance was 4.51 ind./m2, belonging to three phyla and 68 species. Total phosphorus (TP) was the primary environmental driver, reducing functional evenness and dispersion at the alpha level, thereby promoting functional homogenization. At the beta level, TP increased nestedness and decreased turnover, leading to the loss of endemic species and a community dominated by species with broad ecological tolerance. Structural equation modeling showed that TP exerted stronger effects on functional and phylogenetic diversity than on taxonomic diversity. These findings provide multidimensional insights into nutrient-driven biodiversity loss and suggest that TP should be prioritized in water quality management to prevent functional homogenization and maintain beta diversity turnover. Collectively, these findings inform targeted conservation strategies for nutrient-enriched river ecosystems.