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[1] We found a consistent distribution pattern for radiocarbon in dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and methane replicated across spatial and temporal scales in northern peatlands from Minnesota to Alaska. The 14 C content of DOC is relatively modern throughout the peat column, to depths of 3 m. In sedge-dominated peatlands, the 14 C contents of the products of respiration, CH 4 and DIC, are essentially the same and are similar to that of DOC. In Sphagnum-and woody plant-dominated peatlands with few sedges, however, the respiration products are similar but intermediate between the 14 C contents of the solid phase peat and the DOC. Preliminary data indicates qualitative differences in the pore water DOC, depending on the extent of sedge cover, consistent with the hypothesis that the DOC in sedge-dominated peatlands is more reactive than DOC in peatlands where Sphagnum or other vascular plants dominate. These data are supported by molecular level analysis of DOC by ultrahigh-resolution mass spectrometry that suggests more dramatic changes with depth in the composition of DOC in the sedge-dominated peatland pore waters relative to changes observed in DOC where Sphagnum dominates. The higher reactivity of DOC from sedge-dominated peatlands may be a function of either different source materials or environmental factors that are related to the abundance of sedges in peatlands.

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[1] 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 mM early in the season and decreased to $20 mM in July when the water table decreased. Acetate levels increased rapidly to $1000 mM 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 À1 day À1 , which was 7-120 times more rapid than CH 4 production. Experiments utilizing 14 C-acetate confirmed that methanogenesis was not acetoclastic although acetate was converted very slowly to CO 2 . 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. CO 2 production was the most rapid process measured in laboratory incubations (up to 750 nmol mL À1 day À1 ) 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 CO 2 via aerobic respiration and to a much lesser extent anaerobically by Fe reduction.