The effect of different restoration approaches on the soil carbon stock in urban wetlands

Few studies have examined the effect of restoration methods on the soil organic carbon (SOC) stocks in urban restored wetlands. This information is critical for planning and managing wetland restoration projects aimed at preventing carbon loss. The Guangdong Guangzhou Haizhu Wetland, designated as China's only central urban wetland and a Ramsar site, was selected as the study site. The SOC stocks and soil physicochemical factors (0–60 cm) of the mound‐based orchards (orchard control [OC]) and two restored wetlands—shallow freshwater marsh (SFM) and mound‐based orchard wetland (OW)—were analyzed. Results showed that the SOC stocks in urban wetlands were moderate compared to other ecosystems. The mean SOC stocks of different restoration wetlands ranked as follows: OC (116.22 Mg/ha) > OW (93.35 Mg/ha) > SFM (85.70 Mg/ha). SOC stocks and SOC concentrations increased from uplands to lowlands and decreased with soil depth. Notably, the SOC concentration in the 0–10 cm layer of lowland SFM (2.40%) was significantly higher than that of the OW wetland (1.65%). Linear regression analysis revealed that SOC storage in uplands was positively correlated with SOC, total nitrogen (TN), and total phosphorus content, while SOC storage in the lowlands was positively correlated with TN content and negatively correlated with bulk density. These findings highlight that different restoration methods influence SOC storage by altering soil physicochemical properties. Based on the restoration method in SFM, strategically distributing upland and lowland areas, increasing microtopographic variation, and planting aquatic vegetation in lowlands can enhance SOC accumulation quickly.