Anaerobic microbial biogeochemistry in a northern bog: Acetate as a dominant metabolic end product

Abstract

Field measurements and incubation techniques were used to determine the dynamics of acetate formation, iron reduction, and methanogenesis in surficial peat of an Alaskan bog. Acetate concentrations were ∼100 μM early in the season and decreased to ∼20 μM in July when the water table decreased. Acetate levels increased rapidly to ∼1000 μM when the water table rose to the surface in August. Acetate production in anaerobic slurries occurred at rates of 2.8-420 nmol carbon mL-1 day-1, which was 7-120 times more rapid than CH4 production. Experiments utilizing 14C-acetate confirmed that methanogenesis was not acetoclastic although acetate was converted very slowly to CO2. Peat incubated anaerobically for 4.5 months at 24°C never produced methane from acetate, suggesting that anaerobic acetate accumulation would have occurred all season if the water table had remained high. CO2 production was the most rapid process measured in laboratory incubations (up to 750 nmol mL-1 day-1) and appeared to be due primarily to fermentation. Acetate was the primary organic terminal product of anaerobic decomposition in the bog, and acetate was ultimately oxidized to CO2 via aerobic respiration and to a much lesser extent anaerobically by Fe reduction.