X-ray computed tomography of pent soils: measuring gas content and peat structure

The potential of using X-ray computed tomography (CT) to (i) analyse individual biogenic gas bubbles entrapped within peats and (ii) produce reliable descriptors of petit Structure is examined. Existing approaches used to study biogenic gas bubbles measure the gas content of volumes of: peat many orders Of magnitude larger than most bubbles, and are, therefore, Of little use in helping to understand bubble dynamics. In many peatland Studies, the description of peat structures is derived front only a few relatively basic metrics; principally the porosity, the bulk density, and the von Post humification scale. CT is applied to identify and quantitatively analyse the size, location and shape of individual gas bubbles entrapped during the saturation of a 200 cm(3) sample of S. fuscum. 3421 gas bubbles were identified, ranging in size from 0.1 mm(3) to 99.9 mm(3). These gas bubbles were non-randomly distributed, clustered Predominantly in the vertical plane. When analysing the peat Structure, Sphagnum peal in water are shown to be indistinguishable within CT scans. Peat samples were therefore prepared prior to scanning by flushing the peat with lead (II) nitrate solution to increase the linear attenuation of the Sphagnum. Sphagnum stems and branches were analysed, producing metrics of the peat structure including stern and branch lengths, radii and orientation. In a 100 cm(3) sample of S. magellanicum, the length of all Sphagnum sterns totalled 1.82 m, with an average radius of 0.65 mm. The Sphagnum sterns and branches were both preferentially orientated in file horizontal direction. Copyright (C) 2008 John Wiley & Sons, Ltd.