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.
Understanding of erosion and accretion patterns over intertidal mudflats during storm periods is vital for the management and sustainable development of coastal areas. This study aimed to investigate the effect of the 2014 storm Fung-wong on the erosion and accretion patterns of the Nanhui intertidal mudflats in the Yangtze estuary, China, based on field measurements and Delft3D numerical modeling. Results show that prolonged easterly winds during the storm enhance the flood velocity, weaken the ebb velocity, and even change the current direction. The current velocity, wave heights, and bed-level changes increased by 1–1.43 times, 2.40–3.88 times, and 2.28–2.70 times than those of normal weather, respectively. The mudflats show a spatial pattern of overall erosion but increasing erosion magnitude from the high (landward) mudflat to the low (seaward) mudflat during the storm. The magnitude of bed-level change increases with increasing wind speed, but the spatial pattern of erosion and accretion remains the same. The main reason for this pattern is the longer submersion duration of the low mudflat compared with the high mudflat, so the hydrodynamic process is longer and stronger, leading to an enhancement in bed shear stress and sediment transport rate. Wind speed increases the hydrodynamic intensity but does not affect on the submersion duration over each part of the intertidal mudflat. This study is helpful to improve the understanding of physical processes during storms on intertidal mudflats and provides a reference for their protection, utilization, and management, as well as for research in related disciplines.
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