Responses of typical aquatic biological communities to environmental stressors in the Xishui River

For lack of understanding of aquatic bio-environment interactions in the Xishui River, a major tributary of the Chishui River, was studied in this work． Responses of typical aquatic biological communities to environmental factors under combined industrial and agricultural pollution were characterized, to clarify differentiated driving mechanisms on the small-watershed scale, and to propose ecological restoration recommendations． Specifically, species composition, density, and diversity of aquatic organisms were investigated.Redundancy analysis was used to examine their correlations with environmental parameters． The total densities of phytoplankton, zooplankton, and macrozoobenthos at sampling sites were found to range from (1.17-3.85)×10⁶ cell·L⁻¹, 6.05-113.82 ind·L⁻¹ and 966-2 388 ind·L⁻¹, respectively. Biodiversity of plankton was found to be relatively low with spatial variations, while macrozoobenthos diversity remained at a good level with minor spatial differences． Phytoplankton density exhibited significant correlation with ρ(NH₄-N) and ρ(COD_Mn) (p<0.05), while its diversity was found associated significantly with ρ(Hg) and ρ(As) (p<0.05)． Zooplankton density demonstrated highly significant correlation with pH (p<0.01) and significant correlation with ρ(COD_Mn) (p<0.05), its diversity showed significant relationships with ρ(TP) and DO (p<0.05)． Macrozoobenthos diversity was found significantly correlated with ρ(BOD₅), ρ(Hg), and ρ(NH₄-N) (p<0.05)． Comprehensive analysis suggest control measures targeting nutrients from agricultural sources, oxygen-consuming pollutants from industrial sources, and pH regulation to improve the ecological health of the Xishui River．