Sealing of Soils

Abstract

To judge sealing of soil and interventions in locations in the framework of city and water management planning, one needs quantitative data relating to soil properties, climate and water cycles. The assessment of substances is increasingly important, especially if impacts by emission, motor traffic or by abandoned polluted sites have to be considered. In Germany today sealed and built-up areas occupy a significant and increasing fraction of the surface area (>12 %). In this paper various methods to detect sealing are dealt with in detail. Different measurement techniques can give very different numbers about the degree of sealing. Sealing especially affects the natural water cycle. As a rule, sealing reduces actual evapotranspiration and increases surface runoff (canalizing). Sealing also strongly changes the urban heat balance: the higher the building density, the more heat buildup in summer. As compared with the surroundings, on extreme summer days the temperature may increase by ~2–3 K and the saturation deficit of air by ~10–20 %. Sealing of soil also destroys the habitats of fauna and flora. The remaining areas in the city become isolated and develop extreme local conditions. One usually finds a change of fauna and flora, and a shift of the species rank order of abundance. The increased pollutant load in urban spaces, plus the frequent concentration of rainwater into unsealed and partly sealed areas, often causes high pollutant concentrations in the topsoil and in the materials in joints or cracks sin the pavement. High contents of heavy metals in soil and litter may slow down the decomposition of litter, soil respiration, and mineralization.