Establishment and application of ecological health evaluation system for urban and rural rivers in Yangtze Estuary

The assessment of river ecosystem health is crucial for improving river resilience, achieving ecological protection and rational utilization in the Yangtze Estuary region where there is high utilization of rivers and a high demand for quality rivers by Shanghai, the world's largest modern city. To assess the ecological health status of Yangtze Estuary rivers, this study established a river health assessment model consisting of five dimensions: water quality, river landscape, aquatic organisms, river hydrology, and human interference, and a total of ten indicators based on the ecological survey results in the summer and autumn of six river channels in Chongming Island in the Yangtze Estuary. The evaluation results reveal that the health status of rural rivers in the northwest and east of Chongming Island (S2, S3) is the best, reaching an excellent level, while the small river in the central part of Chongming Island (S6) is the worst, reaching a somewhat inferior level. Compared with rural rivers, the comprehensive evaluation results of urban rivers are good or ordinary level. The high proportion of building area on both sides of the river and the low vegetation cover are the main factors that restrict their scoring results. In contrast, rural rivers need to focus on the area of buffer zones such as forests and vegetation on both sides of the river, river connectivity, appropriate widening of narrow rivers, regular cleaning and dredging of rivers, as well as reducing human interference with the rivers. Regarding seasonal changes, the health assessment results of Chongming Island rivers in summer are better than those in autumn, and the differences between sites in summer are slightly greater than those in autumn. The seasonal differences between sites are mainly due to changes in indicators of the diversity of zooplankton, phytoplankton, and macrobenthos. To further improve the ecological health of rivers, measures of ecological restoration could be adjusted based on regular health assessment and health weakness analysis.