Fish Community Characteristics And Ecological Health Assessment Of Major Rivers In Beijing

Based on scientific research and testing,river health assessment plays an important role in aquatic environment monitoring,management and governance,and its results can be used to solve practical problems related to ecological protection.With its rapid socio-economic development and large population base,Beijing is a highly urbanized and strongly human-disturbed region.Water scarcity and water pollution have caused enormous ecological pressure on the rivers.Fish are important indicator organisms for environmental monitoring.The fish biological integrity index system based on fish community species composition,diversity and functional structure characteristics can better reflect the health status and disturbance intensity of aquatic ecosystems.The characteristics of fish diversity,community structure,and ecological niches in the Chaobai River,North Canal,and Yongding River were analyzed using the relative importance index,biodiversity index,ecological niche breadth and overlap,cluster analysis,and the water environmental health evaluated using F-IBI,based on data from four fish diversity surveys from 2021 to 2022.The study results are as follows.（1）From 2021 to 2022,a total of 50 species of fish were identified in the survey,belonging to 40 genera in 7 orders and 15 families.Among them,42 species in the Chaobai River belong to 6 orders and 13 families and 32 genera.35 species in the North Canal belong to 4 orders and 11 families and 27 genera.39 species in the Yongding River belong to 6 orders and 12 families and 30 genera.The survey found five species of key protected fish in Beijing,namely,Gobio rivuloides,Triplophysa dalaica,Gnathopogon mantschuricus,Leuciscus waleckii and Pungitius sinensis.Five endemic fishes in China,namely,Sarcocheilichthys nigripinnis,Squalidus wolterstorffi,Gobio rivuloides,Rhodeus sinensis,and Odontobutis potamophilus.Two exotic species,namely,Perccottus glenii and Silurus meridionalis.（2）The species diversity of fishes in the Chaobai River,the North Canal and the Yongding River all showed strong spatial heterogeneity,and the spatial variation trends were different.The diversity and richness of the lower reaches of the Chaobai River were significantly higher than those of the upper reaches,and the evenness was significantly higher in the upper reaches than in the middle and lower reaches.The spatial distribution of fish diversity in the North Canal was basically the same,all of which were higher in the middle and lower reaches near the Chaobai River system.Fish diversity in the Yongding River was significantly higher in the middle and upper reaches than in the lower reaches.Cluster analysis and non-metric multidimensional scalar ranking analysis showed that the Chaobai River was spatially divided into three communities,and the North Canal and Yongding River were each divided into five communities,with a higher level of community similarity in the North Canal.The results of ANOSIM significance test showed that there were significant differences between the cluster structure groups of all three aquatic systems（P=0.001）.（3）There is some variability in the environmental factors affecting the distribution of fish communities in the three aquatic systems.The environmental factors affecting fish community distribution in the Chaobai River in spring were mainly WT,and in autumn were mainly COD,TP and NH₃-N.There were no significant influencing factors in the North Canal in spring and DO,EC and Sal were the main ones in autumn.There were no significant influencing factors in the Yongding River in spring,Sal and WT were the main ones in autumn.（4）Based on the niche breadth values,cluster analysis was used to classify the dominant fish species into three groups:broad,medium and narrow niche species.The relatively few meaningful species pairs with overlapping ecological niches in the Chaobai,North Canal and Yongding River indicated that the distribution of dominant fish species in the three aquatic systems was highly variable,with high heterogeneity in resource requirements and weak potential competitive relationships among species.（5）Assessment of aquatic ecological health based on F-IBI.The assessment showed that the overall aquatic ecological health of the Chaobai River,the North Canal and the Yongding River were all in good condition.Among them,the grade evaluation criteria Chaobai River>Yongding River>North Canal,and the sampling points with the evaluation grade of excellent were the most numerous in the Chaobai River system.The aquatic ecological health status was Chaobai River>Yongding River>North Canal.