Spatial distribution of microbial methane production pathways in temperate zone wetland soils: Stable carbon and hydrogen isotope evidence

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• 作者：Hornibrook ; Edward R. C. ; Longstaffe ; Frederick J. ; Fyfe ; William S.
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：1997
• 出版时间：February, 1997
• 年：1997
• 卷：61
• 期：4
• 页码：745-753
• 全文大小：957 K

文摘

The identity and distribution of substrates that support CH₄ production in wetlands is poorly known at present. Organic compounds are the primary methanogenic precursor at all depths within anoxic wetland soils; however, the distribution of microbial processes by which these compounds are ultimately converted to CH₄ is uncertain. Based on stable isotope measurements of CH₄ and ΣCO₂ extracted from soil porewaters in two temperate zone wetlands, we present evidence that a systematic spatial distribution of microbial methanogenic pathways can exist in certain anoxic, organic-rich soils. CH₄ production by the acetate fermentation pathway is favored in the shallow subsurface, while methanogenesis from the reduction of CO₂ with H₂ becomes more predominant in older, less reactive peat at depth. This distribution can account for many of the reported CH₄ emission characteristics of wetlands, in particular, their sensitivity to changes in primary productivity, temperature, and hydrology. These factors play an important role in controlling the short-term supply of labile substrates to fermentive methanogens in the shallow subsurface where the most intense CH₄ production occurs. Predominance of the CO₂-reduction pathway at depth may help to explain reports of CH₄ with a semifossil age in lower peat layers.