Diagnostic indicators for characterising urban soil of Szeged, Hungary

Urban soils differ from the natural ones in that they are more strongly influenced by anthropogenic activities. This is especially relevant for Szeged (SE Hungary), where the original surface of the city had been elevated by several meters by the intensive anthropogenic activities (infilling) following the Great Flood of 1879. Samples were taken at 15 sites during the spring of 2005 from horizons of soil profiles located in this city. The major aims of this study were the examination and tracing of the diagnostic properties different from natural soils (i.e. artefacts, humus content, humus quality, pH (H2O, KCl), carbonate content, nitrogen content) from the city centre towards the outskirts. In addition, near the profiles average topsoil samples (0–10 cm depth, 2–4 m2) were also taken for determining heavy metal concentrations in order to assess the “toxic” character [FAO (Food and Agriculture Organization of the United Nations), IUSS (International Union of Soil Sciences), ISRIC (International Soil Reference and Information Centre) 2006. (the first update 2007) World reference base for soil resources. A framework for international classification, correlation and communication, Rome, Italy, pp. 128. ISBN: 92-5-105511-4. (http://www.fao.org/ag/agl/agll/wrb/doc/wrb2006final.pdf)] of the profiles on the one hand, and to differentiate the lithogenic and the artificial origin of these toxic metals on the other. Most of the examined soil parameters are excellent markers of human influence on urban soils. This can be seen either in a change in their recorded concentration values or the alteration of their vertical distribution in the profiles. The large number of artefacts, the low and fluctuating humus and nitrogen levels, the poor quality of the humic material, the higher and fluctuating carbonate content and a concomitant variance in the pH, the modified mechanical properties all refer to soils affected and transformed by human activities. This is also supported by the statistical analysis of the above mentioned parameters indicating human influence. The studied horizons were assigned into natural and anthropogenic categories. It proved possible to distinguish anthropogenic (Cu, Ni, Pb, Zn) and lithogenic (Co, Cr) heavy metals. The anthropogenic elements exceeded the threshold limit values in the studied profiles. Thus, they were categorized as Toxic in accordance with the WRB 2006. The studied urban soils of the city of Szeged have been classified in WRB (2006) with the help of the above mentioned parameters.