METHANE EMISSION FROM A FRESH-WATER 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 me thane emission, as well as in situ methane oxidation were monitored. F rom 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 emissi on data showed that soil moisture was a more important controlling par ameter than soil temperature. Depending on the drainage capacity of th e 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; durin g July. The area with an ''insufficient natural drainage'' had an emis sion of 1.44 mg CH4 m(-2) d(-1). Using methyl fluoride as a specific i nhibitor for methane oxidation, it was found that 34 to 67% of the pro duced methane could be oxidized. Methane emission was found to decreas e with increasing soil depth. With diffusion chambers placed on the so il 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, mo st of the emitted methane was produced in the upper organic soil layer .