Environmental drivers of methane emissions in restored wetlands of the glaciated interior plains

Wetland restoration can recover ecosystem services such as habitat provisioning, water purification and storage, and carbon sequestration, but it can also increase methane (CH 4 ) emissions, creating uncertainty in net climate benefits. We investigated biotic and abiotic drivers of CH 4 emissions from Conservation Reserve Program restored wetlands in the Glaciated Interior Plains of the United States. Twelve wetlands in Ohio, Indiana, and Michigan spanned three Major Land Resource Areas and varied in restoration age, enrollment status, and surrounding land use. Methane fluxes and dissolved CH 4 concentrations in surface water and pore water were measured monthly during the peak growing season from June to August, along with temperature, water depth, and vegetation characteristics. Mean midday growing season CH 4 flux was 4.91 ± 1.75 mg CH 4 m −2 h −1 while median surface water and pore water CH 4 concentrations were 6.10 2.52–23.29 μmol L −1 and 547.45 153.70–2100.50 μmol L −1 , respectively. Pore water CH 4 concentrations were nearly two orders of magnitude higher than surface-water concentrations and differed among vegetation functional types, with submerged-aquatic and floating vegetation having the highest values. Surface water CH 4 concentrations were positively associated with atmospheric CH 4 fluxes, linking dissolved CH 4 pools to realized emissions. After accounting for vegetation functional type, water depth, plant height, month, and random effects, restoration age was modestly but significantly positively associated with CH 4 fluxes, corresponding to an approximately 20% increase over 20 years. Floating vegetation had the highest predicted fluxes, and water depth amplified emissions in tall emergent vegetation. These results identify practical indicators of elevated CH 4 emission risk in restored agricultural wetlands.