Dynamics of soil pore space structure investigated by X-ray microtomography

Transport and transformation processes of solid, liquid and gaseous compounds/components in soils are intimately connected and strongly dependent on the state of soil structure and pore space geometries. Soil structure in turn is inherently dynamic due to changes in pore water pressure resulting in shrinking and swelling and/or soil compaction and shear deformation by applying external loads and last but not least also continuously modified by biological factors (root growth and soil faunal activities). Studying the dynamic properties of soils and functions requires observing the evolution of soil structure with changing boundary conditions without disturbing the processes of structure formation. Non-invasive techniques such as X-ray microtomography are able to resolve soil structure and associated pore architectures on various scales and at the same time allow for non-destructive observations of structural dynamics upon changes in boundary conditions. We used synchrotronand X-ray microfocus tube-based microtomography (SR-μCT and MFμCT resp.) systems to investigate soil structural dynamics of soil aggregates and typical core-size soil samples. The effects of shrinking/swelling and compaction on pore space architectures were studied under controlled boundary conditions (matric potential, mechanical loads). Three-dimensional reconstructions of the pore space were analyzed with 3D image analysis tools to quantify changes in morphological characteristics of soil structure and related pore networks upon changes in boundary conditions, respectively. The potential of such quantitative data to further develop modeling approaches of transport and deformation processes in soils will be discussed. Further improvements in μCT imaging approaches and 3D image analysis of soil structure dynamics coupled with physical measurements of transport functions are essential to achieve a more comprehensive understanding of soil-ecosystem fluxes and interactions.