Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 5 6 2008 10.5194/bg-5-1537-2008 http://www.biogeosciences.net/5/1537/2008/ http://www.biogeosciences.net/5/1537/2008/bg-5-1537-2008.html http://www.biogeosciences.net/5/1537/2008/bg-5-1537-2008.pdf 1537 1549 2008-11-12 Microbial reduction of iron and porewater biogeochemistry in acidic peatlands K. Küsel kirsten.kuesel@uni-jena.de M. Blöthe D. Schulz M. Reiche H. L. Drake Limnology Research Group, Friedrich Schiller University Jena, 07743 Jena, Germany Department of Ecological Microbiology, University of Bayreuth, 95440 Bayreuth, Germany now at: Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, USA Temporal drying of upper soil layers of acidic methanogenic peatlands might divert the flow of reductants from CH4 formation to other electron-accepting processes due to a renewal of alternative electron acceptors. In this study, we evaluated the in situ relevance of Fe(III)-reducing microbial activities in peatlands of a forested catchment that differed in their hydrology. Intermittent seeps reduced sequentially nitrate, Fe(III), and sulfate during periods of water saturation. Due to the acidic soil conditions, released Fe(II) was transported with the groundwater flow and accumulated as Fe(III) in upper soil layers of a lowland fen apparently due to oxidation. Microbial Fe(III) reduction in the upper soil layer accounted for 26.7 and 71.6% of the anaerobic organic carbon mineralization in the intermittent seep and the lowland fen, respectively. In an upland fen not receiving exogenous Fe, Fe(III) reduction contributed only to 6.7%. Fe(II) and acetate accumulated in deeper porewater of the lowland fen with maximum concentrations of 7 and 3 mM, respectively. 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