Abstract
Tidal flats play a critical role in supporting biodiversity and in providing ecosystem services but are rapidly disappearing because of human activities. The Yangtze Estuary is one of the world’s largest alluvial estuaries and is adjacent to the most developed economic zone in China. Using the Yangtze Estuary as a study region, we developed an automatic algorithm to estimate tidal flat areas based on the Land Surface Water Index and the Normalized Difference Vegetation Index. The total area of tidal flats in the Yangtze Estuary has decreased by 36% over the past three decades, including a 38% reduction in saltmarshes and a 31% reduction in barren mudflats. Meanwhile, land claim has accumulated to 1077 km2, a value that exceeds the area of the remaining tidal flats. We divided the Yangtze Estuary into Shanghai and Jiangsu areas, which differ in riverine sediment supply and tidal flat management patterns. Although land claim has accelerated in both areas, the decline in tidal flat area has been much greater in Jiangsu than in Shanghai because of abundant supplies of sediment and artificial siltation in the latter area. The results highlight the need for better coastal planning and management based on tidal flat dynamics.
Highlights
The shoreline or waterline, which is the physical interface of land and water, changes its position continually through time because of sediment transport and tidal cycles[8]
Based on Landsat imagery covering the Yangtze Estuary, we aimed to: (1) develop a processing tool with simple and robust algorithms for the identification of water, land, and vegetation; (2) document the spatial-temporal dynamics of tidal flats and land claim from 1984 to 2014 in two areas of the estuary (Shanghai and Jiangsu) that differ in riverine sediment supply and coastal management patterns; and (3) discuss the potential drivers of the spatial-temporal dynamics of tidal flats
In the past three decades, the total area of tidal flats in the estuary has decreased by 36%, comprising a 38% loss of saltmarshes and a 31% loss of barren mudflats (Fig. 1a–c)
Summary
The shoreline or waterline, which is the physical interface of land and water, changes its position continually through time because of sediment transport and tidal cycles[8]. We mined the temporal series of Landsat images and produced improved maps of water, mudflats, and vegetation in the coastal zone of the Yangtze Estuary. This pilot study demonstrates the potential application of an automatic shoreline algorithm for mapping tidal flats at a large spatial scale. Based on Landsat imagery (path 118/row 38) covering the Yangtze Estuary, we aimed to: (1) develop a processing tool with simple and robust algorithms for the identification of water, land, and vegetation; (2) document the spatial-temporal dynamics of tidal flats (vegetated saltmarsh and barren mudflat) and land claim from 1984 to 2014 in two areas of the estuary (Shanghai and Jiangsu) that differ in riverine sediment supply and coastal management patterns; and (3) discuss the potential drivers of the spatial-temporal dynamics of tidal flats
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