Use of Tomographic Methods for the Study of Urban Soil Properties

Physical properties and their dynamics under anthropogenic impact are important for the rational use of urban soil and its fertility management. However, standard methods and procedures are hardly usable for the modern urban soil science. New methods from other areas of knowledge, such as computer microtomography widely used in geology, biology, and medicine, need to be searched and adapted. The objects of the study are SUITMA soils of Rostov agglomeration and their physical properties, transformed under the effect of industrial, residential, and recreational zones, as well as margin city areas, which were affected by agricultural use. According to the results of studies since 1998, urban soils were grouped into morphological classes of (1) natural-structure soils without urban disturbance, (2) natural-structure soils overlaid by anthropogenic sediments, and (3) soils overlaid by water-impermeable layers. 3D scanning of soil samples was performed on a SkyScan 1172 X-ray scanner at the Dokuchaev Soil Science Institute. Image resolution was 16 µm/pix for the study of internal structure. We used DataViewer and CTan to analyze the images. The samples had natural water content and structure during scanning. Soil samples were then placed in special plastic containers 3 cm in diameter and sealed. Modern analytical methods allow us to analyze separate structural elements, calculate their volume, surface area, amount, and orientation inside of the sample without disturbance. We also can gain data on soil pores (general porosity, open and closed porosities in mm3 or %, pore size and volume and their relationship, pore amount, connectivity). For urban territories in the steppe zone, a comparison of humus-accumulative horizons (A, Asod, Ap, and buried [A] horizons) made it possible to trace tendencies in changes of surface soils under different technogenic and anthropogenic impacts and in the buried and sealed soils. Tomographic data allow us to acquire not only quantitative data, but also visual information.