Meta‐Analysis Indicated a Higher Loss of Soil Active Organic Carbon Fractions in Inland Wetlands Than in Coastal Wetlands After Reclamation in China

ABSTRACT Natural wetlands are widely recognized as important for climate change mitigation, but reclamation can lead to wetland ecosystem degradation and significant changes in soil carbon dynamics. However, how reclamation affects soil active organic carbon (SAOC) fractions and their influencing factors across different wetland types remains unclear. Here, we conducted a meta‐analysis of 838 pairs data from 36 experimental studies in China to compare the changes in soil organic carbon (SOC) and its active carbon fractions (including easily oxidizable organic carbon [EOC], dissolved organic carbon [DOC], and microbial biomass carbon [MBC]) after reclamation in natural coastal and inland wetlands. Results showed that inland wetland reclamation induced substantial losses of SOC and active fractions (SOC, EOC, DOC, and MBC decreased by 36.1%, 38.5%, 56.3%, and 66.5%, respectively), indicating that reclamation mainly influenced the SOC loss by regulating the SAOC dynamics (especially DOC and MBC) in inland wetlands, due to the coupled influences of climate condition and land management. In contrast, coastal wetland reclamation reduced SOC and EOC by 18.7% and 27.8%, but increased DOC and MBC by 3.9% and 12.3%, due to prolonged reclamation reducing seawater salinity and increasing oxygen exposure, enhancing microbial metabolism. In total, coastal wetland reclamation induced less SOC losses (mainly EOC loss) than inland wetland reclamation. Aquaculture was the most significant utilization type for the SOC loss, due to the sudden decrease of carbon inputs caused by vegetation clearing and manure dredging. Our results can contribute to an in‐depth understanding of soil carbon dynamics following reclamation in natural wetlands and provide a theoretical basis for the management of wetland carbon sinks.