China's coastal-wetland change analysis based on high-resolution remote sensing

Abstract

Coastal wetlands not only have abundant biodiversity and high productivity, but they also play an irreplaceable and important role in regional ecosystems. Because of the complex structure and dynamic characteristics of coastal wetlands, it is difficult to observe the spatial changes of coastal wetlands on a large scale and improve data reliability. In this study, a spatially constrained manual-interpretation method based on nationwide high-resolution images in 2017 was adopted to extract China’s coastal wetland distribution, and, then, the second national wetland-survey data from 2011 were used as a baseline for change analysis. The results showed that under the influence of natural conditions and human activities, China’s coastal wetlands have decreased in distribution in the past 6 years. The situation of coastal wetland reclamation is critical, and the hotspot regions are mainly distributed in Bohai Bay, middle of Jiangsu province and Hangzhou Bay. Farming reclamation is another factor that occupies coastal wetlands in China, and main occupied wetlands are mudflats, shallow sea, tidal flats, intertidal salt marshes and estuarine waters. Tide is the main factor affecting extraction of wetlands, the spatially constrained method had a positive effect on wetland detection, and has potential to improve automatic algorithms of complex coastal wetlands.