Adjustment of Effective Water Quality Evaluation Index for Subtropical Urban Rivers

Despite their socio-economic and ecological functions, urban rivers are among the most endangered ecosystems, particularly in developing countries, where population growth, urbanization, and other factors exacerbate the situation. Prolonged and intensive anthropogenic disturbances may enhance organisms' tolerance to pollution in urban rivers. Reliable and effective bioassessment tools are crucial for managing and restoring urban river ecosystems. This study collected macroinvertebrates from a typical urban river in the Pearl River Delta region during the dry season (December 2021 to January 2022) and the wet season (May to June 2022). Family sensitivity values (FSVs) were revised based on local biotic and abiotic data to adjust the Biological Monitoring Working Party (BMWP) and Average Score per Taxon (ASPT) indices. The relationship between biological indices and the Water Quality Index (WQI) was analyzed, and the differences before and after indices adjustment were compared. The results indicated that the revised FSVs for 24 families showed a decreasing trend, with lower FSVs in the dry season compared to the wet season. This pattern reflects the minimum environmental tolerance threshold for macroinvertebrates. Compared to the original indices, the adjusted ASPT exhibited a stronger linear correlation with the WQI in both seasons, while the adjusted BMWP showed a significant correlation only in the wet season, indicating that the adjusted ASPT is more accurate than the adjusted BMWP in evaluating water quality. Therefore, the adjusted bio-indices serve as reliable tools for biological assessment in subtropical urban rivers, enabling effective identification of priority management areas and restoration strategies.