Dynamic changes in soil organic carbon and influencing factors in typical coastal reclaimed wetlands of China

Coastal tidal wetlands are key blue carbon ecosystems with significant carbon sequestration capacity. Understanding the effects of tidal flat reclamation on soil organic carbon (SOC) and its components is essential for informing effective wetland management and policy. This study collected 96 surface soil and sediment samples from Dongtai City, Jiangsu Province, across various land use types, including un-reclaimed tidal flats (0 years) and reclamation sites with 10, 15, 25, 40, and 50 years of reclamation history. Results showed that SOC content generally increased with reclamation age, peaking at 8.92 g/kg after 25 years. While SOC content differences among post-reclamation land use types were not statistically significant, woodland exhibited the highest SOC levels (8.71 g/kg), highlighting its superior carbon sink potential. Additionally, contents of soil dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC), and microbial biomass carbon (MBC) also increased over time. Among these, EOC exhibited the highest average content (1.59 g/kg) across the Dongtai reclamation area. Woodland consistently showed the highest active carbon component content levels (DOC: 4.14 mg/kg, EOC: 2.27 g/kg, MBC: 50.16 mg/kg). Land use type significantly influenced DOC and EOC contents but had no substantial effect on MBC. Environmental factors such as soil moisture, pH, and nitrogen input also impacted SOC dynamics. Notably, nitrogen addition significantly affected SOC and EOC levels in tidal flats and paddy fields, with less pronounced effects on DOC and MBC. These findings provide valuable insight into the long-term impacts of coastal land reclamation on soil carbon pools, with implications for sustainable land management. The study emphasizes the importance of prioritizing land uses with high carbon sink potential, such as woodland, and optimizing soil moisture, pH, and nutrient inputs to enhance carbon pool stability.