Oxidation of Reduced Peat Particulate Organic Matter by Dissolved Oxygen: Quantification of Apparent Rate Constants in the Field.

Peat particulate organic matter (POM) is an important terminal electron acceptor for anaerobic respiration in northern peatlands provided that the electron-accepting capacity of POM is periodically restored by oxidation with O during peat oxygenation events. We employed push-pull tests with dissolved O as reactant to determine pseudo-first-order rate constants of O consumption ( k) in anoxic peat soil of an unperturbed Swedish ombrotrophic bog. Dissolved O was rapidly consumed in anoxic peat with a mean k of 2.91 ± 0.60 h, corresponding to an O half-life of ∼14 min. POM dominated O consumption, as evidenced from approximately 50-fold smaller k in POM-free control tests. Inhibiting microbial activity with formaldehyde did not appreciably slow O consumption, supporting abiotic O reduction by POM moieties, not aerobic respiration, as the primary route of O consumption. Peat preoxygenation with dissolved O lowered k in subsequent oxygen consumption tests, consistent with depletion of reduced moieties in POM. Finally, repeated oxygen consumption tests demonstrated that anoxic peat POM has a high reduction capacity, in excess to 20 μmol electrons donated per gram POM. This work demonstrates rapid abiotic oxidation of reduced POM by O, supporting that short-term oxygenation events can restore the capacity of POM to accept electrons from anaerobic respiration in temporarily anoxic parts of peatlands.