Abstract: A comprehensive evaluation of water quality using both physicochemical and biological approaches is of great importance for water resource management and protection. In this study, we conducted monthly surveys of physicochemical properties and quarterly monitor of benthic macroinvertebrate of Baoying Lake, Yangzhou, Jiangsu Province, during August 2020 to July 2021. We analyzed the relationships between benthic macroinvertebrate community structure and environmental factors, and assessed the aquatic ecological health status of Baoying Lake using acomprehensive trophic level index, comprehensive water quality identification index, and comprehensive biological index based on the entropy weighting method. Results showed that Tanypus chinensis, Propsilocerus akamusi, Limnodrilus hoffmeisteri, Sinotaia purificata and Sinotaia aeruginosa were the dominant species among the 15 species of benthic macroinvertebrates. Chironomidae larvae and Gastropoda predominantly determined the spatiotemporal distribution of density and biomass of benthic macroinvertebrates, respectively. Physicochemical properties except water depth showed no significant spatial difference but strong seasonal variations. Specifically, transparency (SD) was higher in winter compared to other seasons, while permanganate index (COD_Mn) and total nitrogen (TN) were higher in summer than other seasons. SD, COD_Mn, and TN were the main environmental factors affecting the community structure and distribution of benthic macroinvertebrates. The annual nutrient level of Baoying Lake fell within the mesotrophic-moderately eutrophic range. Baoying Lake was at the Class III-IV as indicated by the comprehensive water quality identification index, and at a general to poor state as indicated by the comprehensive biological index. The results of the biological evaluation of water quality were slightly worse than that based on the physicochemical evaluation, indicating that water quality was not the only factor jeopardizing the ecological health of Baoying Lake.

Key words: community structure, comprehensive water quality identification index, entropy weight method, comprehensive biological index