The Urban Soil Properties, Heavy Metal Pollution And Its Changes In Kaifeng City

With rapid process of urbanization, the influence of urban soils on environment and human health is becoming increasingly concerned. In this paper, urban soils sampled from different regions in Kaifeng City were studied on their physical and chemical properties. Based on the concentration of heavy metals, the evaluation of heavy-metal pollution was carried out. Comparing the heavy metal pollution of the same regional urban soil between different times, a cumulative effect of urbanization and industrialization on the urban soil heavy-metal contamination was found. The conclusions are as follows:(1) Comparing with the properties of agricultural soils in the same regional, those of the urban soil were different. The characters of the urban soil profile was more complex; The amounts of intrusions in urban soil was higher markedly; Soil texture was loam mainly with more fine particles; the soil bulk density was smaller and total porosity was bigger; the variation of soil pH was greater; the soil cation exchange capacity was higher; the soil nutrient became richer.(2) The concentrations of all heavy metals in the urban surface layer were higher than those in the suburb soil. The heavy metals content was significant different among the different function zones in Kaifeng City. The concentrations of Cu, Zn, Cr, Pb, Cd, As and Hg were higher in the industrial districts than in other ones; But the concentration of Ni was higher in the administrative/inhabited areas. The distribution of heavy metal in different soil profiles were varied.(3) According to the results of evaluation of heavy metal pollution carried out with two different standards, although we could not made the same conclusions completely, it was sure that the pollution of heavy metals in industrial districts and the areas with more vehicles were evident, especially for Cd and the accumulation of metals happened in urban soil more or less. (4) The heavy metal concentration, except for Ni, was negative correlated with the pH remarkably while its had little relevance with other physics and chemistry properties. There were good positive relationship among As,Hg,Cu,Zn,Cr,Pb,Cd, except for Ni. The heavy metal pollution of the urban soil was caused mainly by the input of anthropogenic sources, for example, wastes and emission generated by industry, the litter discarded from vehicle & living of the residents. The differences of the source of pollution distribution led to the different heavy metals content in the different functional areas soil.(5) According to the analysis of heavy metals content in the very soil profile or the average content of the functional zones, the heavy metals content changed significant in Kaifeng in 1994 and 2006. As a whole, the concentration of As, Hg, Cd, Pd showed an upward tendency in the urban soil, while Cr reduced greatly in most profiles from 1994 to 2006.With the development of urbanization & industrialization, the most heavy metals content in urban soil showed an increasing trend in industrial districts, cultural districts & newly-built city zone. The accumulation of heavy metals in urban soil had a close relationship with the anthropogenic activities which affected environment seriously. However, heavy metals content reduced in some regions for the land-use change,environmental beautification and the improvement of environmental protection infrastructure.Urban soils were closely related to the equality of urban ecological environment, affecting health of citizens. So much more attentions should be paid to urban soil, and more work should be done about its study and management.