HR: 0800h
AN: B11A-1026    [Abstracts]
TI: Stable Isotope Evidence for the Effectiveness of Methanotrophy and the Importance of Plant-Mediated Transport of Methane in Blanket Bogs
AU: * Bowes, H L
EM: H.L.Bowes@bristol.ac.uk
AF: Bristol Biogeochemistry Research Centre, Department of Earth Sciences University of Bristol Wills Memorial Building Queens Road, Bristol, BS81RJ United Kingdom
AU: Hornibrook, E R
EM: Ed.Hornibrook@bristol.ac.uk
AF: Bristol Biogeochemistry Research Centre, Department of Earth Sciences University of Bristol Wills Memorial Building Queens Road, Bristol, BS81RJ United Kingdom
AB: Stable carbon isotope values and rates of methane flux were determined monthly at a blanket bog in Elan Valley, Wales UK during the summer of 2003. The rate and δ¹³C value of methane flux varied between months as a result of changes in soil methanogenesis and methanotrophy caused by shifts in soil temperature and water-table levels. During a period of low water-table levels in July 2003, decreases in flux rates at both Sphagnum- and sedge-rich areas were accompanied by 3 to 4 ‰ increases in δ¹³C values of methane emissions. The flux rate from Sphagnum-dominated surfaces consistently was an order of magnitude less than that from sedge-rich areas. Despite differences in emission rates, the δ¹³C values of methane flux were remarkably similar from both types of vegetated surfaces during each sampling period. Methane flux had very low δ¹³C values (-90.1 to -82.2 ‰) during all months, suggesting that the smaller quantity of methane released from the Sphagnum-dominated surfaces was via the few vascular plants that were present rather than by diffusion through the soil profile where methanotrophy would have caused ¹³C-enrichment of the residual escaping methane. The unusually negative δ¹³C values of methane emissions from the blanket bog appear to be caused by the combined effects of a predominance of methanogenesis via CO₂ reduction linked to H₂ oxidation in soils and stable isotope fractionation during transport through vascular flora. Comparison of δ¹³C values of methane in flux and within pore water at the top of the anaerobic zone indicates that a fractionation of approximately 8 to 12 ‰ occurs during plant-mediated transport at this particular site. The results of this study suggest that the δ¹³C value (-60 ± 5 ‰) currently assumed for methane emissions from peatlands in models of the global methane cycle may be too positive, possibly resulting in the underestimation of methane flux from ¹³C-enriched sources.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0490 Trace gases
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: Fall Meeting 2005