Enhanced Carbon Accumulation in China's New Coastal Wetlands Over the 21st Century

Wetlands formed by natural sediment deposition account for a large proportion of new coastal lands, and these new wetlands usually have active ecosystems and obvious ecological effects. However, previous studies largely overlooked this sediment‐caused wetland expansion, and the spatiotemporal variation in these wetlands and future response to sea‐level rise (SLR) have not been determined. Here, we employed satellite observations to quantify the seaward expansion of coastal lands in China over the past two decades. A total land expansion of 6,651 km2 was found, and wetlands and artificial surfaces dominated, accounting for 32% and 25%, respectively. Subsequently, we utilized an integrated model to estimate the response of these new wetlands to SLR in the 21st century, that is, we estimated the wetland gain from sediment deposition and loss due to SLR. The results indicate that under the current condition of sediment availability, the area of China's new coastal wetlands is projected to increase by 200%–261% compared to that in 2020 based on four SLR scenarios, despite the unavoidable impact of SLR. These increases are accompanied by the continuous enhancement of carbon accumulation. Wetland changes are influenced by factors such as sediment deposition, SLR and storm surges, as well as the continued effect of local natural and anthropogenic factors. These results show the importance of understanding the ecological effects of new wetlands and constructing specific protection measures for sustainable development. Plain Language Summary Compared to anthropogenic reclamation, sediment deposition represents an alternative mechanism for the formation of coastal lands. These newly formed lands possess highly dynamic ecosystems and offer additional land resources, making them immensely important for ecological environments and societal development. This study focused on the spatiotemporal changes in newly formed lands in China's coastal regions over the past two decades, and an examination of the land use status was conducted. The results show that wetlands constitute the predominant component of these new lands, rather than artificial surfaces. Using an integrated model, we estimated the future response of these new wetlands to sea‐level rise and the corresponding carbon accumulation trend. Additionally, the factors influencing the area of new wetlands was analyzed to provide valuable insights and recommendations for future wetland conservation policies. Key Points