摘要 : To clarify how hydrological processes affect biogenic methane (CH4) production andemission from soil surfaces, we analyzed the 613C of CH4 and CO2 and chemicalconstituents dissolved in groundwater at a wetland in the headwater cat... 展开 To clarify how hydrological processes affect biogenic methane (CH4) production andemission from soil surfaces, we analyzed the 613C of CH4 and CO2 and chemicalconstituents dissolved in groundwater at a wetland in the headwater catchment of atemperate forest in Japan. We estimated the contribution of acetate fermentation using the613C isotope mass balance of dissolved CH4 and CO2. CH4 production pathways (e.g.,acetate fermentation and carbonate reduction) changed temporally and spatially withhydrologically controlled redox conditions. The proportion of methanogenesis attributableto acetate fermentation usually decreased with temperature, suggesting that carbonatereduction dominated under conditions of high CO2 concentration. In particular, thegroundwater table and summer temperatures were key controlling factors in theinterannual and intra-annual changes in CH4 production pathways, controlling oxygensupply and consumption and, therefore, redox conditions in the soil. Under hightemperature and high water table conditions during summer, the soil was strongly reducedand the proportion of carbonate reduction increased. Acetate fermentation alsoincreased episodically, resulting in sporadic increases in 613C-CH4. The calculated acetatecontribution obviously decreased in periods of low water table and high temperaturewhen the soil surface was relatively oxic, implying deactivation of acetoclasticmethanogenesis under oxic conditions. Thus, hydrological processes control the supply ofthese electron donors and acceptors and therefore play an important role in determiningthe relative proportions of CH4-producing pathways. Our results also indicate that anincrease in acetate contribution under highly reducing conditions stimulates CH4production and emission from the soil surface. 收起