CH4 and CO2 production relative to carbon burial in wetlands undergoing sediment loss and accretion in coastal Louisiana

The coastal Louisiana region encompasses the largest deltaic system at the mouth of the Mississippi River, in the Gulf of Mexico, and includes the largest wetlands area in the United States. Given the critical functional role of coastal wetlands in carbon (C) storage and sequestration it is essential to assess the potential role of wetlands and adjacent tidal channels as sources (via CH₄ and CO₂ production) and sinks of carbon (via burial) along hydrological gradients. Such information is necessary to construct and constrain landscape-level C budgets. We investigate C burial and CO₂ and CH₄ emissions in two distinct sediment deposition environments undergoing land loss (Barataria Bay) and land formation (Wax Delta) in coastal Louisiana. Sediment cores (depth, 20 cm) were sampled at both sites along tidal channels, ridges and low elevation marshes during spring (March ~10^oC), early summer (May ~20^oC) and late summer (August ~30^oC) to evaluate seasonal and spatial scale variability in CH₄ and CO₂ production. CH₄ production ranged from 0.003 to 20.8 moles/m²/day and differences were correlated to location, ambient temperature, dissolved O₂ concentration in the overlying water and core sediment redox conditions. Seasonal CH4 fluxes into overlying water were significantly higher in the spring compared to the summer season. The CO₂ fluxes ranged from 0.42 to 214 moles/m²/day and also showed higher fluxes at colder temperature (~10 ^o C). These net fluxes will provide valuable information to evaluate the ratio of greenhouse gas production to carbon burial at two contrasting estuarine environments undergoing both loss and net gain of wetland area in coastal Louisiana.