Methane flux from created riparian marshes: Relationship to intermittent versus continuous inundation and emergent macrophytes

Methane's importance as a greenhouse gas warrants examination of the dynamics controlling its emission from temperate zone wetlands created and restored for habitat replacement and water quality improvement. In this one-year field study, hydrology typical of floodplains in the Midwestern USA was simulated in two experimental riparian marshes. Methane fluxes were measured from February to December using non-steady-state chambers located in marsh zones with and without emergent vegetation in which soils were intermittently exposed and inundated, and in permanently inundated wetland areas. Annual methane fluxes from intermittently flooded zones were 30% of fluxes from permanently inundated wetland areas, which emitted ∼42 g CH4-C m−2 year−1. Average growing season rates of methane flux from intermittently flooded zones with and without macrophytes did not differ significantly (∼3.5 mg CH4-C m−2 h−1), but both were significantly less than those from permanently inundated areas (∼8 mg CH4-C m−2 h−1). We suggest that incorporation of seasonal floods followed by drier periods in created riparian wetlands could minimize methane emission.