Effect of entrapped gas on peatland surface level fluctuations

Peat is a highly compressible medium and changes in peat surface level in response to shifts in water storage and entrapped gas volume have been reported previously. Since both peat compressibility and capacity to entrap gas are related to peat structure, we hypothesize that the relationship between water table and surface level may vary across a peatland. The objective of this study is to investigate the relationships between peat surface level positions, water table positions and subsurface gas pools at local topographic low-lying areas within a poor fen, which differ in peat properties and vegetation cover. Three sites were investigated, two with highly movable surfaces (FA and FB) and one which was more stable (NF). Deviations from the water table position-surface level position relationship (residuals) appear to be related to changes in atmospheric pressure. However, this relationship varied between FA and NF. The differences in these relationships were supported by distinct patterns of gas dynamics between these sites. Ebullition tended to occur only during periods of falling atmospheric pressure at FA, whereas it occurred much more frequently at NF without atmospheric pressure being the primary control. Evidence of ebullition based on changes in volumetric water content below the water table were supported by ebullition measured by surface gas traps and by shifts in pore water pressure deviation. These different responses of surface level fluctuations to changes in atmospheric pressure between sampling locations are likely related to variations in peat properties between the sites. Copyright (c) 2006 John Wiley & Sons, Ltd.