Soil carbon gains from salt marsh recovery in China

Coastal salt marshes in China, one of the few countries to achieve net salt marsh gains in recent decades, are important blue carbon ecosystems. However, the lack of national-scale assessments of salt marsh changes and associated soil organic carbon (SOC) dynamics limits our understanding of their climate mitigation potential. Here we show how remote sensing and machine learning quantify changes in salt marsh area and surface SOC across China. Net salt marsh expansion is associated with overall gains in surface SOC, primarily through the conversion of aquacultural ponds, agricultural land and seawater areas, but these gains vary substantially across regions and periods. Salt marsh expansion and protection, particularly within protected areas, are associated with enhanced surface SOC. These findings highlight the importance of conserving existing salt marshes and restoring degraded areas to strengthen coastal carbon sinks. Our approach provides a scalable framework for monitoring spatially explicit SOC changes and supports the integration of salt marshes into national carbon management and broader blue carbon strategies.