Abstract:

Coastal tidal marshes in Shanghai,which are fragile and sensitive to environmental changes,play very important roles in maintaining biodiversity and estuarine ecosystem stability.However,over the last decades they have severely suffered from human activities such as land reclamation.Consequently,the structures and functions of the ecosystems are greatly threatened.In this study,we carried out field surveys as well as remote sensing analysis using Landsat TM/ETM+ data to demonstrate the development dynamics of the tidal marshes and reveal the impacts of diking on these areas in the past 20 years.The results showed:①the tidal marshes in Shanghai are distributed in the coast of the continent and the islands in the Yangtze River estuary,and the area has reached 330.75 km2;②the marshes have been expanding seaward in the past 20 years,and the coastline has been extending as the average annual rate of 100 ～ 300 m eastwards to the sea with the tidal development;③several large reclamation have taken place in the coast in Shanghai in the past 20 years,and the cumulate area of diked marshes is over 653.54 km2 from 1987.The continuous land reclamation have caused the great reduction of the area of wetland and the intertidal vegetation,which have caused great biodiversity loss and ecological degradation.Therefore,for the purpose of wetland conservation,the utilization of the tidal marshes such as land reclamation must follow the principle of dynamic protection,and ecosystem restoration is necessary in the tidal marshes in Shanghai.〖