Erc. Hornibrook et al., SPATIAL-DISTRIBUTION OF MICROBIAL METHANE PRODUCTION PATHWAYS IN TEMPERATE ZONE WETLAND SOILS - STABLE CARBON AND HYDROGEN ISOTOPE EVIDENCE, Geochimica et cosmochimica acta, 61(4), 1997, pp. 745-753
The identity and distribution of substrates that support CH4 productio
n in wetlands is poorly known at present. Organic compounds are the pr
imary methanogenic precursor at all depths within anoxic wetland soils
; however, the distribution of microbial processes by which these comp
ounds are ultimately converted to CH4 is uncertain. Based on stable is
otope measurements of CH4 and Sigma CO2 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 ferm
entation pathway is favored in the shallow subsurface, while methanoge
nesis from the reduction of CO2 with H-2 becomes more predominant in o
lder, less reactive peat at depth. This distribution can account for m
any of the reported CH4 emission characteristics of wetlands, factors
play an important role in controlling the short-term supply of labile
substrates to fermentive methanogens in the shallow subsurface where t
he most intense CH4 production occurs. Predominance of the CO2-reducti
on pathway at depth may help to explain reports of CH4 with a semifoss
il age in lower pear layers. Copyright (C) 1997 Elsevier Science Ltd.