SUTDIESON THE METHANEFLUX ANDITS CONTROLLING IN NATURAL WETLANDS

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Studies on the methane flux and its controlling factor was conducted in two natural wetlands, Kushiro mire and river mouth area of the River Nagara. The former was chosen as the largest and highly natural wetland and the latter was a representative wetland received heavy human impact. In Kushiro mire during field studies in July and August, 1998, methane fluxes in alder moor (14〜17mg/mィイD12ィエD1/h) exceeded those in low moor (9〜10 mg/mィイD12ィエD1/h), where the highest fluxes were usually obtained in the former studies. In August 1999, methane flux were measured in 5 sites with different vegetation in alder moor, and flux range of 2.4 〜15 mg/mィイD12ィエD1/hr and the highest flux was obtained at a site of Equisetum fluviatile, which has the same hollow stalk as reed stem. Stable isotope ratio of carbon (δィイD113ィエD1C) in methane collected from both reed stem and bubble at low moor without vegetation were analyzed and -55.1±0.2 per mil for the former and -59.8±0.8 per mil for the latter were obtained. This result indicates that acetate degradation process was more contributed for reed stem methane, and that HィイD22ィエD2/COィイD22ィエD2 process was more responsible for bubble methane.On the other hand, in the lower reach of the River Nagara, methane fluxes were measured at stations of 3km, 6km (just upper reach of river mouth barrage) and 23km from the river mouth in July 1999, and fluxes of 0.6μg/mィイD12ィエD1/h and 1.7mg/mィイD12ィエD1/h were obtained at 23km and 6km station, respectively. No methane flux was obtained at 3km station. These results indicate that river flow stopping and environment change from brackish to freshwater ecosystem by the construction of river mouth barrage evidently enhanced methane fluxes from lower reach of the river.