Assessment of degradation drivers and conservation effectiveness in China’s salt marsh blue carbon ecosystem

Salt marshes are vital blue carbon ecosystems on Earth, with substantial carbon sequestration capacity that play a crucial role in mitigating global climate warming. However, the dynamics of salt marsh loss and gain and their impacts on carbon sink functions in China at the national scale remain poorly understood. This study integrates field sampling, satellite remote sensing, and machine learning to systematically analyze the spatiotemporal evolution of coastal salt marsh areas and surface SOC in China over the past two decades. This paper focused on revealing how land-use changes and the implementation of national protection and restoration policies have influenced salt marsh area and surface SOC dynamics. The results showed that the area of coastal salt marshes in China followed a significant “first decrease, then increase” trajectory. Salt marsh loss was primarily driven by the expansion of aquaculture ponds and agricultural land, whereas policies such as “returning ponds to wetlands” and “returning farmland to wetlands” facilitated the recovery of salt marsh area. Although the net increase in salt marsh area exhibited spatiotemporally heterogeneous effects on surface SOC, it overall exerted a cumulative promotive effect. Moreover, national protection and restoration policies have effectively mitigated the intensity of human disturbances in China’s coastal areas, emerging as a key driver behind both salt marsh recovery and surface SOC accumulation. These findings provide a scientific basis for scaling up salt marsh conservation and clarifying their roles in blue carbon systems, offering valuable insights for refining wetland protection and climate adaptation strategies.