CHAPTER 7: PHYSICAL AND HYDROLOGICAL PROPERTIES OF URBAN SOILS
(by Dr. Klaus Lorenz and Dr. Rattan Lal)
ABSTRACT: Soils exhibit typical physical and hydrological properties including texture,
structure, water retention and transmission. Soil physical properties and processes
depend on the relative magnitude of solid, liquid and gaseous phases in soil. These
phases are altered by direct and indirect effects of the conversion of natural soils to
urban ecosystems. Alterations include physical disturbance, removal or desurfacing,
burial or coverage of soil by fill material or impervious surfaces; and soil, water and
vegetation management practices (e.g., fertilization, irrigation, mowing, and drainage).
However, changes in the abiotic and biotic environment by urbanization indirectly
influence also soil physical and hydrological properties. For example, the climate is
modified, the soil hydrophobicity is altered, plants and animals are introduced, and a
range of pollutants are introduced. Transformation of natural to urban ecosystems may,
thus, alter soil stratification, soil texture, structure, water retention and transmission, and
probably result in a higher relative proportion of coarse fragments (> 2mm). Urban soils
are characterized by high variability in bulk density and saturated hydraulic conductivity.
With increasing anthropogenic perturbation, the air-filled porosity and, thus, the air
capacity may increase. The field capacity and available water capacity are, however,
often lower due to the high contents of coarse fragments. The ability of urban soils to
store plant available water is important since most urban soils are used for garden, lawn,
park or forest land uses. This chapter provides an overview of the soil physical and
hydrological properties, and on effects of urbanization and human disturbance on this
fundamental soil functions, with a focus on soil hydrological properties.