Water and Heavy Metal Fluxes in Paved Urban Soils [article]

Thomas Nehls, Gerd Wessolek, Technische Universität Berlin, Technische Universität Berlin
2007
Worldwide, the streets and sidewalks in urban areas are often perviously paved. This kind of sealing allows at least a little infiltration of rainwater and thereby decreases the run-off. Pavements consist of the pavers, a construction material and the so called seam material. It was hypothesized, that these three components influence the transport of water and solved substances. The seam material is the first layer of soil material which is situated in the gaps between single pavestones. It was
more » ... pavestones. It was hypothesized, that it develops by incorporation of different deposits of urban dust and that it contains great portions of Black Carbon. This would explain its dark colour. Because of this inputs, the seam material was expected to have a special surface and pore structure. Therefore, special chemical and physical filter properties were expected. Seam materials have been sampled in Berlin, Warsaw and Paris and their properties have been investigated for the first time. Beside the general soil chemical properties, the following parameters have been measured: grain size distribution, pore size distribution and pore structure, specific surface area and surface form, adsorption energy distribution function, and the heavy metal adsorption isotherm. Up to 30% of the organic matter consists of Black Carbon. The organic substance of seam materials has small specific suface area and a low surface charge density. This indicates a non-polar character. The seam material shows a high fractions of low adsorption energy, which proves this statement. However, the seam material shows positive ecological properties compared to the original construction sand: it has a higher available water capacity, a higher cation exchange capacity and shows a higher heavy metal retardation, as seen from the heavy metal adsorption isotherms. From what we know about preferential flow paths, the arrangement of pavers and seams would have to introduce preferential flow patterns. This hypothesis was tested on five sites in Berlin, were brilliant blue coloured w [...]
doi:10.14279/depositonce-1657 fatcat:zr6dw7ze7bdstmyep4zc3r454e