A DNDC Modelling Approach to Soil Organic Carbon: Long-term Dynamics and Century-Scale Responses in an Eastern Chinese Salt Marsh Wetland

Coastal salt marsh wetlands are pivotal blue carbon ecosystems due to their high carbon sequestration capacity resulting from seawater inundation. However, understanding the long-term dynamics of soil organic carbon (SOC) in these regions and driving factors have been hindered by complexities and challenging in SOC modeling. To address this, we applied the Denitrification-Decomposition (DNDC) model to simulate long-term SOC dynamics under varying initial conditions and presented influencing factors of SOC distribution in the Jiangsu coastal wetlands. The results showed that the calibrated DNDC model effectively captured SOC patterns, revealing that Spartina alterniflora marshes led SOC accumulation, followed by Phragmites australis and Suaeda salsa marshes, while tidal flats exhibited a declining trend over time. This divergence is attributed to greater plant biomass input outweighing microbial carbon losses in these vegetated areas, whereas a mechanism absent in unvegetated bare flats. Correlation analysis indicated that soil abiotic characteristics such as total nitrogen, available phosphorus and soil texture were important factors affecting SOC content changes on the whole. Centennial-scale simulations further showed that higher initial carbon content and finer soil textures could delay SOC equilibrium by centuries. This study underscores the value of process-based models in predicting salt marsh wetland carbon content and highlights the need for their application across diverse blue carbon ecosystems to improve stewardship of these vital blue carbon sinks.