Interactions of Dissolved Organic Matter and Reduced Sulfur in Peatland Porewater

HR: 1340h
AN: B33E-1077 [Abstracts]
TI: Interactions of Dissolved Organic Matter and Reduced Sulfur in Peatland Porewater
AU: * Heitmann, T
EM: tobsE_h@web.de
AF: Tobias Heitmann, Limnological Research Station, University of Bayreuth, Universitaetsstr. 30, GEO, Bayreuth, 95440 Germany
AB: In ombrotrophic peatlands sulphate reduction typically accounts for a large fraction of the anaerobic electron flow, despite small pool sizes of sulphate in the pore waters. As a consequence methane production and emissions may be suppressed. The studies objective was to investigate the hypothesis that recycling of sulphur occurs and that redox-reactions of dissolved organic matter (DOM) are involved in the recycling process. The hypothesis was investigated in laboratory experiments and a field study. We reduced reference humic acid with hydrogen sulfide in batch experiments and calculated electron accepting and donating capacities (EAC, EDC), from production of oxidized inorganic sulfur species and reaction with ferric iron to ferrous iron. EAC and EDC were significantly correlated with DOM concentration resulting in 0.58~±~0.09 and 0.63~±~0.15~mmol/gC, respectively. Sulfur was incorporated (1.1~±~0.2~mmol/gC) likely as aryl polysulfide, based on Fourier-transformed infrared (FTIR) spectroscopy. We further determined changes in the in situ redox state of DOM in peat porewater from the Mer Bleue Bog, Ontario, Canada and related these changes to those in dissolved concentrations of sulfate, DOC, acetate, propionate and dissolved inorganic carbon (DIC) and methane. Concentrations of 0.1-2.5 mM (DIC), 0.0-0.8 mM (methane), <~0.005 to 0.12~mM (acetate, propionate), 0.00-0.03~mM (sulfate) and 30-120~mg/L DOC were recorded during the summer of 2004. Methane concentrations seemed to be affected by sulfate concentrations as low as 0.005~mM. The EAC of DOM (0.1-6.0~mmol/gC) generally decreased with depth and was inversely related to the watertable position with highest values in July and lowest in September. Sulfate reduction and methane production may therefore be affected by anaerobic redox reactions of sulfide with DOM.
DE: 0428 Carbon cycling (4806)
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0488 Sulfur cycling
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1890 Wetlands (0497)
SC: Biogeosciences [B]
MN: Fall Meeting 2005