Methane emissions from five wetland plant communities with different hydroperiods in the Big Cypress Swamp region of Florida Everglades

Abstract

The majority of the methane (CH4) emitted from wetlands comes from tropical and subtropical zones. On a global scale, the variability of these emissions had been attributed to water table variations; however, at landscape scales this variability is poorly understood. We measured CH4 fluxes from five characteristic wetland plant communities of southwest Florida representing a gradient in inundation periods. From wettest to driest conditions, communities were designated as deep slough, bald cypress, wet prairie, pond cypress and hydric pine flatwood. Non-steady-state rigid chambers were deployed at each community sequentially at three different times of the day during a 24-month period. CH4 fluxes did not show a discernible daily pattern, in contrast to a marked seasonal increase in emissions during inundation. All wetland communities acted as temporary sinks of CH4, but overall were net sources. Median and mean ± standard error fluxes in CH4-C m-2 d-1 were higher in deep slough (11 and 55.3 ± 21.5), followed by the wet prairie (9.01 and 53.3 ± 26.6), bald cypress (3.31 and 5.54 ± 2.51) and pond cypress (1.49, 4.55 ± 3.35). The pine flatwood community acted as a net sink during the study period (0.0 and-1.22 ± 0.81). Seasonality in CH4 emissions was positively correlated with water levels, but not with soil temperature. However, longer inundation periods did not necessarily result in higher CH4 emissions. These findings add to our current knowledge of CH4 fluxes from subtropical wetland ecosystems and have implications for modeling at ecosystem scales in heterogeneous wetland landscapes.