Trapped methane volume and potential effects on methane ebullition in a northern peatland

Abstract

A novel way of estimating the gas bubble volume in the floating mat sediment of a peatland was developed at Thoreau's Bog in Concord, Massachusetts. Statistically significant relationships between the buoyancy of the floating Sphagnum mat and atmospheric pressure were observed, and these relationships were used to estimate the gas bubble volume. The mass of CH4 stored in gas bubbles is estimated to be as much as 3 times the mass of dissolved CH4, depending on the time of year. The gas bubble volume is frequently large enough to serve as a significant buffer between microbial production of CH4 and the release of CH4 to the atmosphere. Changes in atmospheric pressure, temperature, and water-table elevation may result in modulation of the ebullitive CH4 flux. Periods of rapidly rising atmospheric pressure or equivalent pressure changes due to water-table elevation are capable of arresting bubble volume growth, thereby halting CH4 ebullition. Periods of rapid cooling of the bog could also temporarily halt ebullition, as thermally induced contraction of bubbles and dissolution of CH4 offset bubble volume growth due to methanogenesis.