Invasive Spartina and reduced sediments: Shanghai's dangerous silver bullet

Aims This synthesis paper is developed to provide a summary of ecological, socioeconomic challenges facing the estuarine wetlands within the Yangtze River delta.Methods We combined literature review of the estuarine wetlands and ground measurements of sedimentation, vegetation, and carbon fluxes to illustrate the foreseeable crises in managing these wetlands that play a critical role in Shanghai's urban development. Where the Yangtze River meets the Pacific Ocean, 4.15 × 10 8 mg/year of suspended sediments are deposited along mainland and island shorelines of the 40?000 km 2 delta—resulting in an average growth rate of land outwards 64 m/year since 1951. However, completion of the Three Gorges Dam in 2003, and earlier dam projects, reduced the rates of sedimentation and growth of the islands. To meet the increasing demands for lands and agriculture, policymakers have attempted to enlarge the islands by diking coastal areas and introducing Spartina alterniflora— a grass native to tidal salt marshes of the southeastern USA but exotic to China. Spartina is one of the 16 greatest invasive species listed by the State Environmental Protection Administration of China. Successful plantations and rapid spread of this species have increased the production and fertility of the coast, but at the cost of native ecosystems. We outline the social, economic, and ecological controversies related to this land management strategy in the context of global warming.Important findings Combinations of these changes, including sea level rise, and alterations to storm patterns and long-shore currents, with the continued spread of Spartina, human population growth, and river flow and sediment reduction will make current management untenable.