Abstract: In this paper, the soil organic carbon (SOC) content and its distribution pattern in the natural intertidal zones and reclaimed wetlands of Hangzhou Bay were studied, aimed to explore the effects of vegetation succession, exotic species invasion, and reclamation on the SOC in costal wetlands of the Bay. In intertidal zones, the surface SOC content ranged from 4.41 to 8.58 g·kg^-1, with an average of 6.45 g·kg^-1, and differed significantly under different vegetations, with a tendency of under Phragmites australis (8.56±0.04 g·kg^-1) > Spartina alterniflora (7.31±0.08 g·kg^-1) > Scirpus mariqueter (5.48±0.29 g·kg^-1) > mudflats (4.47±0.09 g·kg^-1); in reclaimed wetlands, the surface SOC content was 7.46±0.25 g·kg^-1 in the 1960s, 1.96±0.46 g·kg^-1 in the 1980s, and 5.12±0.16 g·kg^-1 in 2003, showing a trend of increased after an initial decrease with increasing reclamation year. The SOC in the profiles all showed a decreasing trend from the surface to the bottom. The SOC in intertidal zones and reclaimed wetlands was significantly negatively correlated with soil pH, and positively correlated with soil total nitrogen (TN), suggesting a large reserve of organic nitrogen in TN. The correlation between SOC and soil C/N ratio was not obvious in intertidal zones, but significantly positive in reclaimed wetlands, indicating that reclamation affected soil C/N ratio to a certain extent. This study showed that in the intertidal zones, soil carbon sequestration capacity increased gradually with plant community succession. However, the invasion of exotic species Spartina alterniflora might decrease the capacity of carbon sequestration in intertidal zones. It was also found that the changes of soil moisture content, particle composition, vegetation coverage, and reclamation history were the main factors affecting the SOC distribution in reclaimed wetlands.

Key words: Hangzhou Bay, coastal wetland, vegetation succession, reclamation, soil organic carbon