Ecosystem assessment of semi-natural tidal flat in the Yangtze estuary by pressure-state-response model and fuzzy comprehensive evaluation method

With the development of hydraulic engineering such as harbor, channel and reclamation, more and more natural tidal flat turn into the semi-natural tidal flat (SNTF). How to evaluate ecosystem of semi-natural tidal flat is a scientific problem that has not been fully solved. The study tries to assess ecosystem health change of SNTF adjoining Hengsha East Shoal training dike in the Yangtze estuary. The study found SNTF area > 0m isobaths increased from 30.33 km² in 2010–2014 to 46.66 km² in 2014–2017 and to 56.84 km² in 2017–2020, and the Hengsha Shoal region.0m, -2m and -5m isobaths increased from 174.78 km², 303.82 km², and 556.77 km² in 2010–2014 to 233.34 km², 365.59 km², and 596.83 km² in 2014–2017 and to 243.81 km², 363.27 km² and 567.45 km² in 2017–2020. Using database of 3 pressure indicators, 16 state indicators and 3 response indicators, the study combined pressure-state-response (PSR) model and fuzzy comprehensive evaluation (FCE), constructed a systematic evaluation method of ecosystem health of semi-natural tidal flat. The evaluation result found the ecosystem health of SNTF of Hengsha East Shoal was rated as "Fair" level during 2010–2020, and the summation of comprehensive evaluation index (CEI) increased from 0.4009 in 2010–2014 to 0.4703 in 2014–2017 due to the rapid expansion of tidal flat vegetation, and then decreased to 0.4450 in 2017–2020 due to a reduction in vegetation area caused by erosion. The area of salt marsh vegetation plays an important role in the health of wetland ecosystems. The Hengsha East Shoal ecosystem is undergoing a quickly dynamic evolution processes, long-term series monitoring and further research for this area are necessary to guide its future development according to the tidal flat utilization patterns.