Changes in soil and sediment properties due the impact of the urban environment

Abstract

During our investigation, we analyzed the urban soils from stream banks and sediment of Rak Creek in the area of Sopron, Hungary. The aim of this work was the determination of the anthropogenic influence on a given stream that flows through an urban area (in this case through the city). The assumption was that the streamflow becomes increasingly polluted with toxic elements as it passes through Sopron; we tried to determine the extent to which the stream is polluted. We had 72 urban soil samples at 36 points at 0–10 and 10–20 cm depths on 6 sub-catchments for analyzing the background pollution of Rak Creek. In addition, 6 soil samples from the bank and 12 sediment average samples were taken from the dead region and from the thalweg as well. We analyzed the physical and chemical parameters as well as the heavy metals (e.g., Cd, Co, Cu, Pb, Zn and Ni) in all of the samples. Two element fractions, the total (HNO3+H2O2-extractable) and the available (NH4-acetate+EDTA-extractable) were used for element determination. Toxic elements were measured by ICP-OES in the urban soils and the sediments as well. Urban soils of sub-catchments confirmed the following tendency. On the investigated creek points, the Co and Ni values were below the natural background limits (Cototal 4.90–14.53 mg kg−1, Coavailable 0.64–3.12 mg kg−1; Nitotal 10.77–24.61 mg kg−1, Niavailable 0.75–3.21 mg kg−1). Cutotal content was low except in the case of GYORI point. Pbtotal were under the pollution limit, but Pbavailable were higher than the suggested pollution limit (>25 mg kg−1) in the sediment of thalweg and in the soil of the creek bank at the GYORI site. Summarized, GYORI point was the most polluted; this is also confirmed by the enrichment factor (EF). EF for Pb and Zn increased as we moved toward the city. Based on the investigated properties, there were significant differences in heavy metals between the urbanized and non-urbanized areas. The concentrations of heavy metals were higher in the dead region than in the thalweg except for the GYORI samples. According to our results, the city affects the stream and its influence appears in the values: as soon as the stream reaches the city, most of results increase. Therefore, the degree of heavy metal contamination depends mainly on land use.