Effect of nutrient enrichment on alpha and beta diversity of macroinvertebrate community in a boreal river of northern China

Nutrient enrichment has long been recognized as a major threat to freshwater ecosystems. Mounting evidence suggests that nutrient enrichment leads to a decline in the biodiversity and functional homogenization of species, manifested as a decline in alpha or beta diversity indices. While several studies have investigated the effects of nutrient enrichment on the biodiversity of macroinvertebrates, the comprehensive analysis of taxonomic, functional, and phylogenetic diversity at the alpha and beta levels remains relatively scarce. Therefore, data on macroinvertebrate assemblage structure and environmental factors were collected in northern Chinese rivers to elucidate the response of their multidimensional biodiversity to nutrient enrichment. The results revealed that as the most significant environmental factor, an increase in total phosphorus levels not only reduced functional evenness and dispersion within the community at the alpha level, leading to the functional homogenization of the benthic community but also enhanced the nested components and reduced the turnover component of the assemblage at the beta diversity level. This shift resulted in the loss of endemic species, which stabilized the community structure. However, this community, composed of universal species, markedly reduces the ecosystem's resistance to environmental changes. Additionally, by constructing a structural equation model, the effect of nutrient enrichment was found to be more pronounced on functional and phylogenetic diversity than taxonomic diversity. Collectively, these findings provide valuable insights for integrated research and the conservation of macroinvertebrate diversity in nutrient-enriched river ecosystems.