The anthropogenic sealing of soils in urban areas

The sealing of soils by impervious materials is, normally, detrimental to its ecological functions. Exchanges of energy, water and gases are restricted or hampered and an increasing pressure is being exerted on adjacent, non sealed areas. The negative effects span from loss of plant production and natural habitats to increased floods, pollution, and health risks and consequently higher social costs. Environmental Agencies produce periodical reports where the phenomenon of soil consumption by urban infrastructures is monitored with extremely sophisticated geographical tools but little specific research is available that describes the effects of soil sealing. This paper reviews some recent contributions in terms of definition, phenomenology, and conceptual and empirical modeling approaches to artificial soil sealing with a special focus to urban areas of Europe. The works about the effects of soil sealing on soil functions are then considered, in particular those that affect the energy transfer, water and gas movements and the biota. Soil sealing is also examined as a tool for protecting some environmental compartment from contamination. In general, porosity, color, geometry of the materials used in the sealing of soils, the quality of sealed soil and aspect ratio of urban infrastructures are key aspects in preserving soil functions.