Methane and carbon dioxide fluxes in created riparian wetlands in the Midwestern United States: Effects of hydrologic pulses, emergent vegetation and hydric soils

Wetlands are important ecosystems involved in the global carbon cycle as producers and consumers of the greenhouse gases methane and carbon dioxide. The global warming potential of methane---23 times greater than that of carbon dioxide over a 20 year time horizon---warrants examination of the dynamics controlling its emission from temperate zone wetlands created and restored for habitat replacement and water quality improvement. Research on carbon dynamics in created and restored ecosystems can enable greater understanding of management practices to promote carbon sequestration in these ecosystems. In the research conducted for this dissertation, ecosystem and mesocosm-scale investigations were carried out in experimental riparian wetlands of the Midwestern USA, with hydrology, vegetation and soils as independent variables. Methane and carbon dioxide fluxes were the dependent variables of interest in each of the studies. In a one-year field study, flood-pulse hydrology typical of floodplains in the Midwestern USA was simulated in two one-hectare riparian marshes. Methane fluxes were measured from February-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 yr-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).; In an extension of the first, one-year study, methane and carbon dioxide flux rates were measured in the morning, afternoon and nighttime in the same experimental marshes over a second year during which hydrologic inflow was maintained at a relatively constant rate. Under these 'steady-flow' conditions, approximately the same total volume of inflow was delivered as during the flood-pulse year.; The hydrology and physiochemical properties of soils forming the foundation for created and restored wetlands determine what processes are likely to occur in these systems. In a companion, replicated study, effects of intermittent vs. continuous inundation, and hydric vs. non-hydric soils on fluxes of methane and carbon dioxide were investigated using 20 wetland mesocosms. The hydrologic treatments represented contrasting wetland restoration scenarios, and the soil treatments represented newly created and established wetlands. Hydric soils and continuously inundated treatments exhibited the greatest methane flux, while intermittently inundated conditions reduced methane fluxes significantly from hydric soils. (Abstract shortened by UMI.)...