Spatiotemporal Changes and Driving Factors of China’s Coastal Marsh during 2000–2020 based on Open Datasets

Coastal wetlands face dual threats from climate change and human disturbances, while they provide important ecosystem functions and deliver essential ecosystem services. Exploring the drivers behind coastal wetland changes will benefit sustainable coastal ecosystem management. Based on GlobaLand30 data, this study systematically assessed the spatiotemporal changes and drivers of China’s coastal marsh changes during 2000–2020 by incorporating land-use transformation process and various anthropogenic and environmental factors from public datasets. Our findings revealed a net increase of 865.8 km² in coastal marsh area during 2000–2020, with distinct regional variations. Coastal marsh changes were more evident north of 30°N, particularly in the Bohai Rim region (37–41°N) and the Yangtze River Delta (30–33°N). Over 75% of major coastal marsh gains (> 1,250 ha) and losses (> 1,000 ha) based on 25 km² hexagonal grids occurred in these two regions during 2000–2020. The increase in the proportion of major coastal marsh loss grids (> 1,000 km²) from 80.0% to 89.8% in these two regions during 2010–2020 suggests that some areas continued to deteriorate, highlighting that total area changes may mask important local dynamics. While driving factors varied across latitudes, land reclamation remained the dominant reason for coastal wetland loss. Reclamation induced coastal marsh loss accounting for over 60% of the total losses across all sea regions during different periods. In the Bohai Rim, the latitudinal distribution of marsh losses aligned with aquaculture changes patterns, while marsh gains primarily resulted from ecological recovery. In the East China Sea region where the Yangtze Delta is located, accretion contributed over 65% of total gains during both 2000–2010 and 2010–2020 periods. The areas of significant coastal marsh changes in the East China Sea region spatially overlapped with the distribution range of Spartina alterniflora. Based on the analysis of driving forces and ecological issues, this study proposed region-specific adaptive management strategies. Future research should strengthen the quantitative analysis of multiple driving forces’ interactions to provide a scientific basis for developing more targeted land-sea management strategies.