Abstract
Abstract. Depositions of all kinds of urban dirt and dust including anthropogenic organic substances like soot change the filter properties of the seam filling material of pervious pavements and lead to the formation of a new soil substrate called seam material. In this study, the impact of the particular urban form of organic matter (OM) on the seam materials CECpot, the specific surface area (As), the surface charge density (SCD), the adsorption energies (Ea) and the adsorption of Cd and Pb were assessed. The Cd and Pb displacement through the pavement system has been simulated in order to assess the risk of soil and groundwater contamination from infiltration of rainwater in paved urban soils. As, Ea and SCD derived from water vapor adsorption isotherms, CECpot, Pb and Cd adsorption isotherms where analyzed from adsorption experiments. The seam material is characterized by a darker munsell-color and a higher Corg (12 to 48g kg-1) compared to the original seam filling. Although, the increased Corg leads to higher As (16m2g-1) and higher CECpot (0.7 to 4.8cmolckg-1), with 78cmolckg-1C its specific CECpot is low compared to OM of non-urban soils. This can be explained by a low SCD of 1.2×10-6molc m-2 and a low fraction of high adsorption energy sites which is likely caused by the non-polar character of the accumulated urban OM in the seam material. The seam material shows stronger sorption of Pb and Cd compared to the original construction sand. The retardation capacity of seam material for Pb is similar, for Cd it is much smaller compared to natural sandy soils with similar Corg concentrations. The simulated long term displacement scenarios for a street in Berlin do not indicate an acute contamination risk for Pb . For Cd the infiltration from puddles can lead to a breakthrough of Cd through the pavement system during only one decade. Although they contain contaminations itself, the accumulated forms of urban OM lead to improved filter properties of the seam material and may retard contaminations more effectively than the originally used construction sand.
Highlights
In urban areas, sealing of soil surfaces leads to ecological problems caused by the increased and accelerated runoff and reduced evapotranspiration compared to non-sealed soils
Ea and surface charge density (SCD) derived from water vapor adsorption isotherms, CECpot, P b and Cd adsorption isotherms where analyzed from adsorption experiments
This can be explained by a low SCD of 1.2×10−6 molc m−2 and a low fraction of high adsorption energy sites which is likely caused by the non-polar character of the accumulated urban organic matter (OM) in the seam material
Summary
In urban areas, sealing of soil surfaces leads to ecological problems caused by the increased and accelerated runoff and reduced evapotranspiration compared to non-sealed soils. At heavy rainfalls the exceeding water causes mixed sewage systems to run over This is one of the main threats to water quality of urban water bodies (Heinzmann, 1998). Run off reduction by increasing infiltration is among the main ideas of ecological urban planning. In many European cities, especially in the older parts, they are regularly found. They keep the convenience for the city dwellers but allow infiltration rates of 58 cm d−1 for a mosaic tile pavement with 20 % of seams, until 155 cm d−1 for so called grass pavers having a coverage of open seams of up to 41% (Wessolek and Facklam, 1997)
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