The expansion of Spartina alterniflora marsh in response to tidal flat reclamation, central Jiangsu coast, eastern China

The central Jiangsu coast is typical of China's coastal muddy silt with an average tidal range of 4 m. The shoreline has been gradually advancing seaward as the coast was supplied by a large amount sediment from ancient Yangtze River and Yellow River. As a result, a lot of land resources are fostered in the coast. Therefore tidal flat reclamation activities gradually intensified to the demand of economic development. A large- scale reclamation plan in Jiangsu coast has been implemented since the 21 st century and Spartina alterniflora marsh has become the main target of tidal flat reclamation. Thus how Spartina alterniflora marsh will expand during the reclamation period is worthy of study. Thirteen phases of satellite imageries from 2001 to 2013 and field observation data are analyzed to quantify the expansion rate of Spartina alterniflora marsh in association with the reclamation activities. The result shows that Spartina alterniflora expansion during 2001- 2013 can be divided into three periods. During 2001- 2007,the Spartina alterniflora area outside the seawall was relatively large and the influence on the tidal flat sedimentary environment by reclamation did not hamper its expansion. As a result,both the annually increased Spartina alterniflora area and the expansion rate keep pace with reclamation. During 2008- 2010, the Spartina alterniflora area outside the seawall decreased significantly; nevertheless, the mean annual expansion rate of the Spartina alterniflora marsh was still relatively high. During 2011- 2013, the area of Spartina alterniflora marsh became small because of the reclamation activities during 2001-2007 and 2008-2010 periods. Spartina alterniflora expansion became stabilized. As such, the pattern of the marsh expansion differs in response to the reclamation rate and stages. If a sufficiently wide marsh can be maintained during reclamation, then the marsh will continue to grow. The underlying mechanism is that the Spartina alterniflora marsh is influenced by the generation of seedling and the sediment types and bed elevation, while reclamation will affect all these factors. The relationship between marsh expansion and reclamation rate for the period of 2001- 2007 indicates that, for sustainable reclamation on the Jiangsu coast, a width of 0.9-1 km for the Spartina alterniflora marsh should be maintained.