Hindawi Publishing Corporation Archaea Volume 2012, Article ID 896727, 9 pages doi:10.1155/2012/896727 Research Article Archaeol: An Indicator of Methanogenesis in Water-Saturated Soils Katie L. H. Lim, 1 Richard D. Pancost, 1 Edward R. C. Hornibrook, 2 Peter J. Maxfield, 1 and Richard P. Evershed 1 1 Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre and The Cabot Institute, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK 2 Bristol Biogeochemistry Research Centre and The Cabot Institute, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK Correspondence should be addressed to Richard D. Pancost, r.d.pancost@bristol.ac.uk Received 21 August 2012; Accepted 16 October 2012 Academic Editor: Michael Hoppert Copyright © 2012 Katie L. H. Lim et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Oxic soils typically are a sink for methane due to the presence of high-affinity methanotrophic Bacteria capable of oxidising methane. However, soils experiencing water saturation are able to host significant methanogenic archaeal communities, potentially affecting the capacity of the soil to act as a methane sink. In order to provide insight into methanogenic populations in such soils, the distribution of archaeol in free and conjugated forms was investigated as an indicator of fossilised and living methanogenic biomass using gas chromatography-mass spectrometry with selected ion monitoring. Of three soils studied, only one organic matter-rich site contained archaeol in quantifiable amounts. Assessment of the subsurface profile revealed a dominance of archaeol bound by glycosidic headgroups over phospholipids implying derivation from fossilised biomass. Moisture content, through control of organic carbon and anoxia, seemed to govern trends in methanogen biomass. Archaeol and crenarchaeol profiles differed, implying the former was not of thaumarcheotal origin. Based on these results, we propose the use of intact archaeol as a useful biomarker for methanogen biomass in soil and to track changes in moisture status and aeration related to climate change. 1. Introduction Methane (CH 4 ) emission from soil is determined by the net balance of simultaneous in situ production of biogenic CH 4 by methanogenic Archaea and consumption by methan- otrophic Bacteria. In the majority of oxic soils, methanotro- phy far outweighs internal CH 4 production. The latter is assumed to be low or negligible as, although methanogens are known to survive in aerobic soils [1], they are tradition- ally considered strict anaerobes [2] which if present in soil are confined to anoxic microsites. Consequently, any CH 4 pro- duced typically is oxidised before reaching the atmosphere. Nonetheless, soils exposed to wet conditions can host sub- stantial methanogenic communities, and in some instances act as a source of CH 4 emissions, despite extended periods of oxygen exposure [3–6]. Consequently, we postulate that in situ CH 4 production could be underestimated in such water-saturated soils, and furthermore, marginal increases in wetting caused by climate-change induced precipitation may increase the capacity of a water-saturated soil to act as a net CH 4 source rather than a sink for atmospheric CH 4 . Thus, it is important to further understand the presence and distribution of microbial populations controlling CH 4 production in water-saturated soil in order to assess their potential to respond to changes in soil moisture and aeration conditions, and long-term impacts of climate change. Membrane lipids of Archaea in cultures have been exten- sively studied and the distribution of their lipid component parts may be used for taxonomic purposes [7, 8]. Intact polar lipids (IPLs) are considered important biomarkers for living microbial biomass as polar head-groups covalently bound to the core lipid are degraded relatively quickly