Abstract
Tidal flats, which are non-vegetated land–sea transition areas, have an important ecological function in the global ecosystem. However, they have been shrinking in recent years due to natural and anthropogenic activities. Although many studies focus on tidal flats in the Yangtze River estuary (YRE) in China, how reclamation and plant invasion affect the expansion and erosion of tidal flats are still unclear. In this study, we analyzed all of the available Landsat TM/ETM+ /OLI imagery from the period 1996 to 2018 using the Google Earth Engine (GEE) cloud computing platform to obtain annual maps of coastal tidal flats of YRE at 30 m spatial resolution. We chose three sample tidal flats where severe Spartina alterniflora (S. alterniflora) invasion, reclamation, and control areas existed to explore the joint impact of plant invasion and reclamation on tidal flats. We also point out the main driving factor of tidal flat expansion of each island in YRE by multiple linear regression. Our results suggest that the tidal flats of YRE had obvious expansion from 1996 to 2018, and the speed of expansion is getting slower because of the decreasing deposits in the Yangtze River. Invasive S. alterniflora is effective at promoting silting, and tidal flats with S. alterniflora invasion expanded 2.54 times faster than the control group. Chongming and Hengsha Islands were mainly affected by sediment concentration, while Changxing and Jiuduansha Islands were affected by reclamation and S. alterniflora invasion, respectively. The results could be used to support coastal zone management and biodiversity conservation of the YRE.
Highlights
Coastal tidal flats are land–sea transition zones neighboring coastal vegetation areas, and are usually referred to as non-vegetated coastal areas
The study area is located at the mouth of the Yangtze River in eastern China, between 31◦05 –31◦40 N and 121◦40 –122◦10 E, including Chongming Island (CMI), Changxing Island (CXI), Hengsha Island (HSI), and Jiuduansha Island (JDSI)
This paper demonstrated the spatial and temporal dynamics of tidal flats in Yangtze River estuary (YRE) during 1996–2018 using the Google Earth Engine (GEE) cloud computing platform, analyzing the effects of invasion by S. alterniflora and reclamation on the expansion and erosion of tidal flats
Summary
Coastal tidal flats are land–sea transition zones neighboring coastal vegetation areas, and are usually referred to as non-vegetated coastal areas. Coastal tidal flats often serve as important habitats for zoo-benthos (crabs, nematodes, mollusks, etc.), fish, waterfowl, and migrating birds [1,2,3,4,5]. They help prevent coastal erosion and protect terrestrial ecosystems from storms and other natural disasters, due to their location as a buffer zone [6]. The erosion of tidal flats can stem from many factors, such as reduced sediment supply from rivers, sinking estuary deltas, rising sea levels, artificial projects, and biological invasion [9,10,11,12,13], the most important of which are reclamation and plant invasion [14]. Large-scale reclamation causes a decrease in large areas of tidal flats
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