Examination of Vesicular Porosity in Desert Soils Using High-Resolution X-Ray Computed Tomography.

Vesicular horizons are a common type of surface horizon in desert soils, characterized by the abundance of vesicular pores, which occur as nearly spherical non-interconnected pores.  The pore morphology of vesicular soils is easily altered by disturbance of the soil surface, but the pores have been observed to reform on a short time scale and may play a role in ecosystem recovery from disturbance.  In this study, the pore morphology of soils with vesicular horizons was examined using high-resolution X-ray computed tomography.  Vesicular horizons from different desert ecoregions were examined, as well as vesicular horizons from undisturbed locations, tire tracks, and bioturbated coppice dunes soils.  Using computed tomography we were able to distinguish three different pore shapes that are characteristic of vesicular horizons: vesicles, vughs, and horizontally interconnected pore networks.  These pore types can be distinguished by the application of a volumetric form of the lobation ratio, based on the relationship between surface area and volume of the pores.  Vesicles and vughs occupied more of the sample volume and were larger in size in the soils of the Great Basin, relative to the Mojave and Sonoran Deserts.  Vesicles and vughs in the tire tracks were relatively unaltered compared to surrounding undisturbed vesicular horizons, in contrast vesicular horizons buried beneath coppice dunes showed a collapse of vesicles and vughs and increased number of interconnected pores.  These results demonstrate that computed tomography is an effective way to characterize the pore morphology of vesicular horizons and their response to different types of disturbance.