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Lake Fukami-ike is a small eutrophic lake in central Japan and the lake water stratfies from April to October. The methane flux and vertical-horizontal distributions of dissolved methane were studied starting in March 1999. The vertical distribution of dissolved methane indicates the methane is produced in the hypolimnion, and the competition with sulfatereducing bacteria is clearly seen as hydrogen sulfide concentration increase. High dissolved methane concentrations were often found in the epimnion and hypolimnion in this lake. The high methane concentrations in the bottom layer were released from the bottom sediments (max. about 26.7 CH4 μl g-1), with a corresponding decrease in the acetic acid concentrations. The phenomenon in which there was a high methane concentration and methane flux was often seen in the surface layer. The horizontal dissolced methane distribution in the surface in the surface of lake water was not found to be affected by run off from the lake shore., Article, 信州大学山地水環境教育研究センター研究報告 2: 75-78(2004)