Analysis of methane production pathways in a riparian wetland of a temperate forest catchment, using δ13C of pore water CH4 and CO2
Analysis of methane production pathways in a riparian wetland of a temperate forest catchment, using δ13C of pore water CH4 and CO2
复制标题
DOI：
10.1029/2007jg000647
复制
发表时间：
2008-09
影响因子：
--
通讯作者：
Masayuki Itoh;N. Ohte;K. Koba;A. Sugimoto;M. Tani
中科院分区：
文献类型：
--
作者：
Masayuki Itoh;N. Ohte;K. Koba;A. Sugimoto;M. Tani
[1] 为了阐明水文过程如何影响土壤表面生物甲烷 (CH4) 的产生和排放，我们分析了日本温带森林源头集水区湿地地下水中溶解的 CH4 和 CO2 的 δ13C 以及化学成分。我们利用溶解的 CH4 和 CO2 的 δ13C 同位素质量平衡估算了醋酸盐发酵的贡献。 CH4 生产途径（例如乙酸盐发酵和碳酸盐还原）随着水文控制的氧化还原条件而在时间和空间上发生变化。醋酸盐发酵产生的甲烷比例通常随温度的升高而降低，这表明在高CO2浓度条件下碳酸盐还原占主导地位。特别是，地下水位和夏季气温是 CH4 生产途径年际和年内变化的关键控制因素，控制着氧气的供应和消耗，从而控制土壤中的氧化还原条件。夏季高温高水位条件下，土壤还原强烈，碳酸盐还原比例增大。乙酸发酵也间歇性增加，导致 δ13C-CH4 偶尔增加。当土壤表面相对含氧时，计算出的醋酸盐贡献在低地下水位和高温时期明显下降，这意味着在含氧条件下醋酸碎屑产甲烷作用失活。因此，水文过程控制着这些电子供体和受体的供应，因此在确定 CH4 产生途径的相对比例方面发挥着重要作用。我们的结果还表明，在高度还原条件下乙酸盐贡献的增加刺激了土壤表面 CH4 的产生和排放。
[1] To clarify how hydrological processes affect biogenic methane (CH4) production and emission from soil surfaces, we analyzed the δ13C of CH4 and CO2 and chemical constituents dissolved in groundwater at a wetland in the headwater catchment of a temperate forest in Japan. We estimated the contribution of acetate fermentation using the δ13C isotope mass balance of dissolved CH4 and CO2. CH4 production pathways (e.g., acetate fermentation and carbonate reduction) changed temporally and spatially with hydrologically controlled redox conditions. The proportion of methanogenesis attributable to acetate fermentation usually decreased with temperature, suggesting that carbonate reduction dominated under conditions of high CO2 concentration. In particular, the groundwater table and summer temperatures were key controlling factors in the interannual and intra-annual changes in CH4 production pathways, controlling oxygen supply and consumption and, therefore, redox conditions in the soil. Under high temperature and high water table conditions during summer, the soil was strongly reduced and the proportion of carbonate reduction increased. Acetate fermentation also increased episodically, resulting in sporadic increases in δ13C-CH4. The calculated acetate contribution obviously decreased in periods of low water table and high temperature when the soil surface was relatively oxic, implying deactivation of acetoclastic methanogenesis under oxic conditions. Thus, hydrological processes control the supply of these electron donors and acceptors and therefore play an important role in determining the relative proportions of CH4-producing pathways. Our results also indicate that an increase in acetate contribution under highly reducing conditions stimulates CH4 production and emission from the soil surface.