Controls on methane production in a tidal freshwater estuary and a peatland: Methane production via acetate fermentation and CO₂ reduction

Rates of total methane production, acetate fermentation and CO₂ reduction were compared for two different wetland sites. On a per-liter basis, sediments from the White Oak River estuary, a tidal freshwater site in eastern North Carolina, had an annual methane production rate (53.3 mM yr^-1) an order of magnitude higher than that of Buck Hollow Bog (5.5 mM yr^-1), a peatland in Michigan. Methane was produced in the White Oak River site on an annual basis by both acetate fermentation (72%) and CO₂ reduction (28%) in a ratio typical of freshwater methanogenic sites. Competition for acetate by non-methanogenic microorganisms in Buck Hollow peat limited methane production from acetate to only a few months a year, severely impacting annual methane production rates. However, when acetate was available to the methanogens in the peat during early spring, the percentage of methane production from acetate fermentation (84%) and CO₂ reduction (16%) and rates of total methane production were similar to those of the White Oak River sediments at the same temperature. Rates of CO₂ reduction and acetate fermentation conducted at both sites at various temperatures showed that Buck Hollow peat methane production was also limited by a colder temperature regime as well as differences in the response of the CO₂ reducing and aceticlastic methanogens to temperature variations.