Natural wetlands store a substantial amount of carbon (C) in the soil; however, because of human activities, over half of the world’s wetlands were lost during the 20th century, resulting in a net release of soil C to the atmosphere. Wetland restoration and creation efforts have been widely attempted to compensate for wetland losses and recover wetland functions, but there has to date been no comprehensive evaluation of the efficacy of soil C and nitrogen (N) recovery in the regional scale. This meta-analysis synthesizes 41 articles to identify the general patterns of soil C and N change after wetland restoration or creation in the conterminous United States.
Results/Conclusions
We found that soil C to soil depths ≤30 cm may attain natural wetland levels 30-40 years following restoration or creation, while soil N attains natural levels after 20-25 years. As soil sampling depth increases, more time is needed for soil C and N to reach natural levels. Soil C and N in riverine wetlands and temperate climate may recover faster than in depressional wetlands and cold climate. Linear regression analysis revealed a positive relationship between the effect sizes of restoration or creation on soil C and N, indicating that wetlands may alleviate N limitations intrinsically during C recovery processes. Additionally, there was a positive relationship between the effect sizes of restoration or creation on soil C at soil depths ≤10 cm and 10-30 cm, indicating that soil C recovery at 10-30 cm can be extrapolated from data at ≤10 cm. Our analysis suggests that restoration and creation projects are potentially efficient for mitigating soil C and N losses in degraded wetlands. Soil C and N recovery would depend on the time since wetland restoration or creation, soil depth, landscape position and climate.