Abstract
Wetlands are natural sources of methane (CH4) emissions, with the majority of those releases in tropical and subtropical regions. Land-use modifications can change a wetland’s hydroperiod and hydrologic connectivity, among two important factors controlling methanogenesis. I measured CH4 fluxes from soils in two southwestern Florida cypress (Taxodium) swamps. Three research sites were in a highly protected strand of cypress in Corkscrew Swamp Sanctuary and three were on the campus of Florida Gulf Coast University. Campus sites had experienced modifications in land use well before the campus was constructed in the 1990s. Net methane emissions were measured twice daily 10 times from January through December 2014. Mean ± standard error net methane fluxes were 25.9 ± 15.6, 22 ± 21.8, and 49.5 ± 24.7 (mg CH4-C m-2 d-1 ) for the reference bald cypress slough, pond cypress slough and cypress dome, respectively, and 4.0 ± 3.8, -1.4 ± 0.8, and 0.5 ± 0.5 (mg CH4-C m-2 d-1 ) for the disturbed pond cypress slough, cypress dome 1 and cypress dome 2, respectively. The only median flux different than 0 was at the reference cypress dome (12.9 mg CH4-C m-2 d-1). Fluxes from the reference sites were significantly higher than fluxes from the disturbed sites. Deeper water and higher soil temperatures at the time of sampling, by themselves, did not necessarily explain higher CH4 fluxes. More continuous surface flooding at the reference sites compared to seasonal flooding at the disturbed sites appear to be the main cause for higher methane emissions at the reference sites.