3 - Muddy Coast Off Jiangsu, China: Physical, Ecological, and Anthropogenic Processes

Abstract

Mudflat covers more than 90% of the 954-km Jiangsu Coast. Even without any major river sediment input, the majority of the Jiangsu Coast has been advancing seaward for more than a century, making it an extremely unique coastal system. Under the influence of physical, ecological, and anthropogenic processes, mudflat of the Jiangsu Coast has experienced rapid changes during the past half century. Here we summarized and discussed the key factors that contributed to the development, maintenance, and change of the mudflat, with emphasis on the impacts of unique hydrodynamics, strong interaction with salt marshes, and intensive human intervention. The key points are summarized as follows. (1) The unique convergent and divergent tidal currents in the middle coast, together with the strong flood-dominant tidal asymmetry and lower energy environment due to sheltering from offshore sand ridges, result in a net landward sediment transport. The evident seasonal variation of wind, wave, and shelf currents determines the seasonality of the sediment transport in the Jiangsu Coast. (2) Eroded sediments from the abandoned Yellow River delta in the north, the ancient Yangtze River delta in the south, and radial sand ridges in the east are the major sediment sources that have sustained the continuous accretion and seaward advancement of the mudflat in the middle Jiangsu Coast for more than one century. (3) Evidence demonstrates that the fine sediment accumulation in the lower-middle intertidal mudflat has been dramatically enhanced by salt marsh, especially Spartina alterniflora that was introduced to the Jiangsu Coast in 1979. The Spartina alterniflora marsh sequesters carbon, traps nutrients, regulates contaminants, and generates new land, but it also reduces biodiversity and degrades the local ecosystem. (4) Human intervention, particularly the intensive reclamation activities since the 1950s, has greatly shrinked the mudflat. Average width of the mudflat decreased from more than 10km in the 1980s to 2km presently, due to reclamation activities. With accelerated sea-level rise, coastal protection infrastructures in the northern and southern coasts, damming in the local rivers, and long-lasting erosion of the offshore sand ridges, the sediment supply is decreasing and the seaward advance of the mudflat is likely to be limited in the future.