Characterization of structural disturbances in peats by X‐ray CT‐based density determinations

Abstract

Summary Bulk density was determined indirectly in peat samples by X‐ray computed tomography (X‐ray CT) and compared with density values obtained by standard laboratory methods. Five Histosols were collected in the same cut‐over peatland, representing various degrees of disturbance related to the process of peat extraction. Soil cores were fully imaged by X‐ray CT with a voxel size of about 0.25 mm. Each one of these five attenuation profiles was analysed and compared with direct density measurements. A linear relationship, to convert attenuation values into density values, is proposed to determine the variation in bulk density with a spatial resolution clearly greater than standard laboratory determinations. It is also shown that X‐ray‐based density values can be effectively used to characterize the structure of peat soils and the possible consequences of disturbances after drainage and peat mining. Under the accepted limitations of the method, X‐ray CT opens up new opportunities to determine the structural quality of peat and to monitor its modifications with time. This indirect diagnostic could be particularly useful to study peatlands' hydraulic systems or evaluate the effectiveness of restoration measures.

The effect of pore structure on ebullition from peat

“…Therefore, these metrics were discounted because they do not help distinguish between peats that have similar overall porosities but different pore size distributions and pore connectivity. To obtain this additional information, studies have adopted methods including slicing and imaging peat sections [ Quinton et al ., ] or imaging the entire peat samples using X‐ray computed tomography [ Rezanezhad et al ., ; Kettridge and Binley , ; Turberg et al ., ]. Of the methods available, X‐ray computed tomography is the least intrusive and provides fine spatial resolution images of peat structure in two or three dimensions.…”

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

“…Because of an overlay of the scan slices, the space between consecutive slices was 0.3 mm. The 5 freeze-cores were all scanned with the same parametrization of the scanner, which was specifically developed for geomaterials and already used in Turberg et al (2014) and Amossé et al (2015b). X-ray beams emitted from the rotating scanner source were focused on a 1.2 mm focal spot with a peak energy of 120 KeV and a tube current of 500 mA.…”

“…The soil bulk density of each frozen subsample was measured with the Sand Density method described in detailed in Turberg et al (2014). A precise metal recipient with known mass and volume (V cylinder = 196.35 cm 3 ) was initially completely filled with a homogenous, finely textured sand and weighted to determine the density of the sand.…”

“…Studying peat soil structure and various types of loamy and silty soils respectively, Turberg et al (2014) and Rogasik et al (2003) have shown the potential to observe changes in soil bulk density based on variations in voxel intensity. Based on the visual identification of different soil units from the previously drawn profiles and from the X-ray CT cross sections the direct correlation between the voxel intensity and the frozen wet soil bulk density has also been demonstrated in the present analysis.…”

“…The process of CT image acquisition is described in detail in Ketcham and Carlson (2001). CT scans provide a 3D intensity map of the soil where gray level variations are essentially related to changes in material density (Rogasik et al, 2003;Sander et al, 2008;Turberg et al, 2014). In the following text, the term radiodensity, as a commonly-used term to measure the transparency of a material to X-rays, will be used to refer to the soil bulk density imaged by X-ray data and expressed by changes in gray level values.…”