Iron, sulfur, and dissolved carbon dynamics in a northern peatland

Abstract

We examined the aqueous and solid-phase biogeochemistry of three different types of northern peatland sediments (oligotrophic bog, beaver pond, and transition site) along a peatland transect in Ontario, Canada. Pore water concentrations (pH, Fe 2+ , Fe 3+ , SO 4 2-, H 2 S, CH 4 , CO 2 and fatty acids) were monitored seasonally, solid phase profiles (Fe(II), Fe(III), reduced inorganic sulfur) measured, and potential rates of CO 2, CH 4 , Fe 2+ , and H 2 S production determined in slurries of peat. Dissolved CO 2 (up to 6 mmol/L) and CH 4 (up to 1 mmol/L) were the predominant species at all sites. In the acidic bog acetate (up to 1 mmol/L) and smaller quantities of propionate and butyrate were present in the pore water. Dissolved Fe 2+ (<5-150 μmol/L), SO 4 2- (10-50 μmol/L), and H 2 S (0 to 10 μmol/L) concentrations were much lower in comparison. The Fe(II) production rates (0.6-7.2 mmol m -2 d -1 ) were small compared to production rates of CO 2 (38-46 mmol m -2 d -1 ) and CH4 (14-29 mmol m -2 d -1 ). Low concentrations of reactive Fe(III) (5-75 μmol/g) suggested that the Fe(II) reduction rate was limited by reactive Fe(III). In slurries amended with sulfate (0.5 mM) the potential for sulfate reduction was substantial and rates of CH 4 production decreased by 48 - 86 %. The in situ accumulation of acetate, propionate and butyrate in the acidic bog was consistent with a lack of stimulation of CO 2 and CH 4 production during anaerobic incubation amended with acetate. Despite differences between sites Fe reduction was overall of little significance for the carbon flow. Sulfate reduction might have been more important based on the results from the incubations. In the bog, the accumulation of acetate and propionate confirmed the decoupling of anaerobic metabolic processes and the important role of fatty acid dynamics in the carbon cycle of acidic northern peatlands.