mechanistic study on responses of typical aquatic biological communities to environmental stressors in the Xishui River Watershed

To address the insufficient understanding of aquatic bio-environment interactions in the Xishui River, a major tributary of the Chishui River, this study aims to analyze the response characteristics of typical aquatic biological communities to environmental factors under combined industrial and agricultural pollution in small watersheds, clarify the differentiated driving mechanisms at the small-watershed scale, and propose ecological restoration recommendations. Taking the Xishui River as the study area, this research investigated the species composition, density, and diversity of aquatic organisms and applied redundancy analysis to examine their correlations with environmental parameters. The results indicated that the total densities of phytoplankton, zooplankton, and macroinvertebrates at sampling sites ranged from 1.17~3.85×10⁶ cells·L⁻¹、6.05~113.82 ind·L⁻¹ and 966~2388 ind·L⁻¹, respectively. The biodiversity of plankton was relatively low and showed spatial variations, while macroinvertebrate diversity remained at a good level with minor spatial differences. Phytoplankton density exhibited significant correlations with NH₄-N and COD_Mn (p<0.05), while its diversity was significantly associated with Hg and As (p<0.05). Zooplankton density demonstrated a highly significant correlation with pH (p<0.01) and a significant correlation with COD_Mn (p<0.05), and its diversity showed significant relationships with TP and DO (p<0.05). Macroinvertebrate diversity was significantly correlated with BOD₅, Hg, and NH₄-N (p<0.05). Based on comprehensive analysis, this study proposes 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.