Effect of atmospheric pressure and temperature on entrapped gas content in peat

Entrapped biogenic gas in peat can greatly affect peatland biogeochemical and hydrological processes by altering volumetric water content, peat buoyancy, and 'saturated' hydraulic conductivity, and by generating over-pressure zones. These over-pressure zones further affect hydraulic gradients which influence water and nutrient flow direction and rate. The dynamics of entrapped gas are of global interest because the loss of this gas to the atmosphere via ebullition (bubbling) is likely the dominant transport mechanism of methane (CH4) to the atmosphere from peatlands, which are the largest natural terrestrial source per annum of atmospheric CH4. We investigated the relationship between atmospheric pressure and temperature on volumetric gas content (VGC) and CH4 ebullition using a laboratory peat core incubation experiment. Peat cores were incubated at three temperatures (one core at 4 degrees C, three cores at 11 degrees C, and one core at 20 degrees C in sealed PVC cylinders, instrumented to measure VGC, pore-water CH4 concentrations, and ebullition (volume and CH4 concentrations). Ebullition events primarily occurred (71% of the time) during periods of falling atmospheric pressure. The duration of the drop in atmospheric pressure had a larger control on ebullition volume than the magnitude of the drop. VGC in the 20 degrees C core increased from the onset of the experiment and reached a fluctuating but time-averaged constant level between experiment day 30 and 115. The chance in VGC was low for the 11 degrees C cores for the initial period of the experiment but showed large increases when the growth chamber temperature increased to 20 degrees C due to a malfunction. The core maintained at 4 degrees C showed only a small increase in entrapped gas content throughout the experiment. The 20 degrees C core showed the largest increase in VGC. The increases in VGC occurred despite pore-water concentrations of CH4 being below the equilibrium solubility level. Copyright (C) 2009 John Wiley & Sons, Ltd.