 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1436-8730/06/0102-16 16 DOI: 10.1002/jpln.200521724 J. Plant Nutr. Soil Sci. 2006, 169, 16–24 Pore-system characteristics of pavement seam materials of urban sites Thomas Nehls 1 *, Grzegorz Jozefaciuk 2 , Zofia Sokolowska 2 , Mieczyslaw Hajnos 2 , and Gerd Wessolek 1 1 Institute of Ecology, Dept. of Soil Conservation, Technical University of Berlin, Salzufer 12, D-10587 Berlin, Germany 2 Institute of Agrophysics of Polish Academy of Sciences, Doswiadczalna 4, 20–290 Lublin, Poland Accepted November 27, 2005 PNSS P172/4B Summary The original light-brown sandy seam filling of pavements in urban areas turns dark and changes its properties by the time due to various inputs of urban dust. Deposited C org inputs do mostly not have natural characteristics but are man-made, e.g., diesel dust. Thus, properties of the seam material are not predictable from experiences with forest or agricultural soils. Semiperviously sealed urban areas are sites of conta- minant deposition as well as groundwater recharge. For an assessment of the resulting groundwater-contamination risk in these areas, the properties of the seam material, which influences transport processes, must be known. The aim of this study was to investigate the pore-system build-up, which includes size distribution and fractal character in the seam material of urban sites. The investigated samples were taken from pavements adjacent to roads in Berlin and Warsaw. The micropore parameters (nanometer range) were charac- terized using water-vapor desorption isotherms, mesopore parameters (micrometer range) were estimated from mer- cury-intrusion porosimetry and macropore parameters (milli- meter range) from water-retention curves. Particle density, dry bulk density, and particle-size distribution were measured using standard methods. Volumes of micro- and mesopores as well as particle densities and dry bulk densities correlated with C tot contents. However, no such relation was found for macropore volumes. Compared to the original sandy seam filling, the altered seam material shows significantly higher C org contents and higher amounts of micro- and mesopores. Therefore, the available water capacity increases by 0.05– 0.11 m 3 m –3 , as compared to the original sandy seam filling. Compared to natural sandy soils having similar C org contents, the seam material shows similar macropore volumes, but the volume of mesopores and micropores is a few times smaller. That is mainly because of the particulate character of the organic matter. Key words: seam material / porosity measurements / semipervious sealing / water-vapor desorption isotherms / pavement 1 Introduction Although it is convenient for the city’s population, soil sealing is one of the most frequent and drastic soil alterations in urban areas, leading to a number of ecological and finally economical problems. Compared to natural environments, the surface runoff increases and infiltration decreases. The consequences are fast and pronounced responses in the dis- charge of receiving water courses, which can be flood-rele- vant. Furthermore, it can cause overrunning of combined sewage systems, which induces pollution of urban rivers with untreated wastewater (Heinzmann, 1998). The result of the decreased infiltration is a smaller amount of available soil water for the evapotranspiration. This leads to higher sensi- ble heat and smaller latent heat: the city becomes hotter (Wessolek, 2001). The mean annual temperature increases by 0.5–1 K with absolute maximum differences of up to 10 K compared to surrounding nonsealed and green areas (Kuttler, 1998). Hotter urban climate leads to human-health problems and to increased macroeconomic costs in these areas (Tol, 2002; Townsend et al., 2003). Therefore, increas- ing rainwater infiltration is a main idea of ecological urban planning. Pervious sealing (e.g., cobblestones, concrete slabs with open seams) can help to reach this goal: Compar- ed to impervious soil sealing, e.g., concrete or tar, seams allow at least little exchange between the sealed soils and their environment including gas exchange, water infiltration, and solute fluxes (Wessolek, 2001). These processes are mainly determined by the seam percentage and the age of the seam material. With increasing age, the original seam fill- ing (usually coarse sand) becomes less conductive (Borg- wardt, 1993; Wessolek and Facklam, 1997) due to accumula- tions of different species including foliage, diesel dust, oil, etc. Whether these accumulations can fulfill positive filter functions has not been studied yet. However, it is known that because of the emissions caused by traffic and industry, the rainwater runoff on semiperviously sealed urban areas is often contaminated (Dannecker et al., 1990). Furthermore, the groundwater recharge under semiperviously sealed areas can be even higher than under nonsealed soils, because of the reduced evaporation (Gugla et al., 1999). This phenom- enon potentially results in high pollutant loads, even if pollu- tant concentrations in the soil solution are low. Semipervious pavement systems are constructed to be highly conductive by using materials which are weak in retention, but its upper layer, the dark seam material, which is rich in C org , may act as a filter. Therefore, it may strongly influence all exchange processes and the water behavior in the pavement system. Although some physical characteristics and infiltration capa- cities of different pavements have been investigated (Schramm, 1996; Wessolek and Facklam, 1997), characteris- tics of the pore system of seam materials have not been stu- died yet. Thus, the database for a risk assessment and for modeling the behavior of water in the pavement is missing. Our objective is to investigate physical and ecological proper- ties of seam materials and to obtain data that allow modeling * Correspondence: Th. Nehls; e-mail: thomas.nehls@tu-berlin.de