B11H-0536
Production of Excess CO2 relative to methane in peatlands: a new H2 sink

Monday, 14 December 2015
Poster Hall (Moscone South)
Rachel Wilson1, Ben J. Woodcroft2, Ruth K Varner3, Gene W. Tyson2, Malak M Tfaily1, Steven Sebestyen4, Scott R Saleska5, Kelsey Rogers1, Virginia Isabel Rich5, Karis J McFarlane6, Joel E Kostka7, Randy K Kolka4, Jason Keller8, Colleen M. Iversen9, Suzanne B Hodgkins1, Paul J Hanson9, Tom Guilderson6, Natalie Griffiths9, Florentino de La Cruz10, Patrick M Crill11, Jeffrey Chanton12, Scott D Bridgham13 and Morton Barlaz10, (1)Florida State University, Tallahassee, FL, United States, (2)University of Queensland, St Lucia, Australia, (3)University of New Hampshire Main Campus, Durham, NH, United States, (4)U.S. Forest Service, Grand rapids, MN, United States, (5)University of Arizona, Tucson, AZ, United States, (6)Lawrence Livermore National Laboratory, Livermore, CA, United States, (7)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (8)Chapman University, Orange, CA, United States, (9)Oak Ridge National Laboratory, Oak Ridge, TN, United States, (10)North Carolina State University, Raleigh, NC, United States, (11)Stockholm University, Dept. of Geological Sciences, Stockholm, Sweden, (12)Florida State Univ, Tallahassee, FL, United States, (13)University of Oregon, Eugene, OR, United States
Abstract:
Methane is generated as the end product of anaerobic organic matter degradation following a series of reaction pathways including fermentation and syntrophy. Along with acetate and CO2, syntrophic reactions generate H2 and are only thermodynamically feasible when coupled to an exothermic reaction that consumes H2. The usual model of organic matter degradation in peatlands has assumed that methanogenesis is that exothermic H2-consuming reaction. If correct, this paradigm should ultimately result in equimolar production of CO2 and methane from the degradation of the model organic compound cellulose: i.e. C6H12O6 à 3CO2 + 3CH4. However, dissolved gas measurement and modeling results from field and incubation experiments spanning peatlands across the northern hemisphere have failed to demonstrate equimolar production of CO2 and methane. Instead, in a flagrant violation of thermodynamics, these studies show a large bias favoring CO2 production over methane generation. In this talk, we will use an array of complementary analytical techniques including FT-IR, cellulose and lignin measurements, 13C-NMR, fluorescence spectroscopy, and ultra-high resolution mass spectrometry to describe organic matter degradation within a peat column and identify the important degradation mechanisms. Hydrogenation was the most common transformation observed in the ultra-high resolution mass spectrometry data. From these results we propose a new mechanism for consuming H2 generated during CO2 production, without concomitant methane formation, consistent with observed high CO2/CH4 ratios. While homoacetogenesis is a known sink for H2 in these systems, this process also consumes CO2 and therefore does not explain the excess CO2 measured in field and incubation samples. Not only does the newly proposed mechanism consume H2 without generating methane, but it also yields enough energy to balance the coupled syntrophic reactions, thereby restoring thermodynamic order.

Schematic of organic matter degradation. Solid lines indicate traditional pathways from Conrad (1999), dashed lines indicates new proposed mechanism.

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