Responses of methane emissions to global wetland restoration and influencing factors

Wetlands are among the largest sources of methane (CH₄) on Earth. To restore degraded ecological functions, wetland restoration has been implemented worldwide, but its impact on CH₄ emissions remains poorly understood. This study conducted a comprehensive global meta-analysis, integrating data from 59 field studies, to assess CH₄ emission responses to wetland restoration and identify key influencing factors through subgroup analyses and structural equation modeling (SEM). Our results indicated that CH₄ emissions increased by 122.3 % after wetland restoration compared to disturbed wetlands but remained 21.17 % lower than those of natural wetlands. Across all subgroup analyses, CH₄ emissions of restored wetlands were neither significantly lower than those of disturbed wetlands nor significantly higher than those of natural wetlands. The total greenhouse gas emissions of restored wetlands were not higher than those of disturbed wetlands but were significantly lower than those of natural wetlands (−22.92 %), primarily influenced by CH₄ and CO₂ emissions. CH₄ emissions were particularly sensitive to disturbance and restoration in freshwater wetlands, peatlands, and wetlands with seasonal flooding, high nutrient contents, or colder climates. In contrast, saline wetlands exhibited no significant changes in CH₄ emissions post-restoration. The SEM analysis identified restored hydrology, salinity, soil pH, restored type, and restored years as the dominant factors influencing CH₄ emissions, with climate exerting only indirect effects. These findings underscore the importance of rewetting (to water table depths of at least −15 cm), sustained restoration efforts (lasting at least 5 years), and the recovery of natural vegetation (rather than selective species planting) for effective wetland recovery. CH₄ emissions without these measures were significantly lower than those of natural wetlands. This study offers in-depth insights into CH₄ emissions following wetland restoration, providing a scientific foundation for wetland management strategies and CH₄ emission assessments under global change scenarios.