Effect of environmental conditions on methane and nitrous oxide fluxes of two South African wetlands

Since the pre-industrial era atmospheric concentrations of greenhouse gases have increased considerably. Wetlands, as a source of atmospheric methane and nitrous oxide, play an important role in the global carbon and nitrogen cycle. Due to their slow decomposition rate of organic matter under anaerobic conditions, wetlands store significant quantities of carbon from the atmosphere in their soils. Fluxes of greenhouse gases from wetland soils are mainly influenced by water table, temperature and carbon content and are an important component in the biogeochemical processes of wetlands. The majority of research on greenhouse gas emissions from wetland soils is located in the northern hemisphere. There is no published research in this topic available from southern Africa. Fluxes of greenhouse gases from two wetlands with a hydrological gradient were sampled with the ‚closed chamber‘ method and analyzed with a gas chromatograph. Besides the gaseous fluxes, several environmental parameters such as the carbon and nitrogen content of the soil as well as ground water level, soil water chemistry and soil temperature were measured. General wetland soils showed significantly higher fluxes of methane and nitrous oxide than non wetland soils. For methane fluxes the ground water level acted as an ‚on-off switch‘ located about 10 cm below the soil surface with surprisingly short response time. Furthermore, a linear relationship between soil temperature and methane fluxes was observed at one site. Ground water level was, however, the dominating factor influencing the greenhouse gas emissions throughout.