Abstract
As the home to national nature reserves and a Ramsar wetland, the tidal flats of the Yangtze River Delta are of great significance for ecological security, at both the local and global scales. However, a comprehensive understanding of the spatiotemporal conditions of the tidal flats in the Yangtze River Delta remains lacking. Here, we propose using remote sensing to obtain a detailed spatiotemporal profile of the tidal flats, using all available Landsat images from 1974 to 2018 with the help of the Google Earth Engine cloud platform. In addition, reclamation data were manually extracted from time series Landsat images for the same period. We found that approximately 40.0% (34.9–43.1%) of the tidal flats in the study area have been lost since 1980, the year in which the tidal flat area was maximal. The change in the tidal flat areas was consistent with the change in the riverine sediment supply. We also found that the cumulative reclamation areas totaled 816.6 km2 and 431.9 km2 in the Yangtze estuary zone and along the Jiangsu coast, respectively, between 1974 and 2018. Because of reclamation, some areas (e.g., the Hengsha eastern shoal and Pudong bank), which used to be quite rich, have lost most of their tidal flats. Currently, almost 70% of the remaining tidal flats are located in the shrinking branch (North Branch) and the two National Nature Reserves (Chongming Dongtan and Jiuduansha) in the Yangtze estuary zone. Consequently, the large-scale loss of tidal flats observed was primarily associated with reduced sediment supply and land reclamation at the time scale of the study. Because increasing demand for land and rising sea levels are expected in the future, immediate steps should be taken to prevent the further deterioration of this valuable ecosystem.
Highlights
Tidal flats are among the most important ecosystems in the world [1]
We explored the impact of influencing factors, including reclamation, estuarine projects, sediment supply, and relative sea-level rise, which may affect the spatiotemporal dynamics of the tidal flats
The changes were generally consistent with changes in the riverine sediment load (r2 = 0.489), whereas the reclamation had a significant influence on the loss of tidal flats
Summary
Tidal flats are among the most important ecosystems in the world [1]. They play an irreplaceable role in water purification, carbon sequestration, biodiversity conservation, and storm surge protection [2,3].Tidal flats are highly vulnerable ecosystems and are sensitive to global change [4].Human activities and natural forces have led to a loss of approximately 25–50% of the world’s tidal flats [5,6], and it is predicted that they will continue to be lost at a substantial rate in the future decades [4].Because tidal flats are alternately submerged and exposed to air by tides and consist of unconsolidated sediments, they are a highly dynamic environment, thereby providing limited access for researchers.it is difficult for traditional measurement techniques to obtain sufficiently extensive data in tidal flats. Tidal flats are among the most important ecosystems in the world [1]. They play an irreplaceable role in water purification, carbon sequestration, biodiversity conservation, and storm surge protection [2,3]. Because tidal flats are alternately submerged and exposed to air by tides and consist of unconsolidated sediments, they are a highly dynamic environment, thereby providing limited access for researchers. It is difficult for traditional measurement techniques to obtain sufficiently extensive data in tidal flats. Our knowledge concerning these ecosystems at the regional and local scales is
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