Methane emission from a freshwater wetland in Belgium

Some factors influencing methane emission from a freshwater wetland in Belgium were studied. Seasonal fluctuations of methane emission rates, influence of drainage capacity and depth of methane production on methane emission, as well as in situ methane oxidation were monitored. From March until December, methane fluxes varying between 0 and 102 mg CH4 m(-2) d(-1) were measured. During this period, a total emission of 60 kg CH4 ha(-1) was calculated. Statistical analysis of these emission data showed that soil moisture was a more important controlling parameter than soil temperature. Depending on the drainage capacity of the selected area, different emission rates were observed. Sites with a ''bad natural drainage'' and a ''fairly bad natural drainage'' showed average fluxes of 5.41 and 2.04 mg CH4 m(-2) d(-1) respectively; during July. The area with an ''insufficient natural drainage'' had an emission of 1.44 mg CH4 m(-2) d(-1). Using methyl fluoride as a specific inhibitor for methane oxidation, it was found that 34 to 67% of the produced methane could be oxidized. Methane emission was found to decrease with increasing soil depth. With diffusion chambers placed on the soil surface, a CH4 release of 40.0 kg CH4 ha(-1) (March-June) was found. With chambers placed at 150- and 300-mm depths, emission rates of 11.3 and 3.3 kg CH4 ha(-1), respectively, were calculated. Obviously, most of the emitted methane was produced in the upper organic soil layer.