Distribution Of Heavy Metals And Microbial Activities In Urban Topsoils From Different City Zones Of Nanjing

Much attention has been paid to the pollution of urban soils, but we still know little of its microbial habitat. In this research, the Nanjing city was divided into six zones as smelter industry, inner commercial, inner residence, newly developed, urban greenland and preserved scenic zones. We analyzed the soil microbial biomass C and N, urease activity and catalase activity in these six zones to study the influencial factor on the distribution and variation and discuss the significance of urban soils as microbial habitat, the indication of soil quality and environmental quality. The results showed C-biomass and N-biomass is higher in urban greenland, preserved scenic areas and lower in newly developed and inner commercial zones. The principal components analysis showed urease activity, C-biomass and catalase activity contributed greatly to the principle factors. Compared to agricultural soil, both the ratio of C/N and Cmic/Corg has an enlarged range in urban soils of Nanjing city. All of these proved urban ecology and environment had been disturbed by anthropogenic stress and microbial community may be changed.In addition, we studied the total concentrations of Cu, Zn, Pb and the available concentrations extracted by DTPA and the distribution in different city zones. We analyzed the relationship between microbial biomass, Cmic/Corg, enzyme activity and heavy metals to negotiate the effect of heavy metals on the soil microbial properties and the bioindication of environmental change. The results showed that the soils were polluted with Cu, Zn to some extent and heavily polluted with Pb. The microbial biomass (based on Corg ) was significantly negatively correlated with heavy metals Cu and Pb, but with Zn.this negative correlation was; not significant. The Cmic/Corg was also significantly negatively correlated with Cu, Zn and Pb. Both the urease activity and catalase enzyme activity were not negatively coirelated with heavy metals. The available heavy metals has a closer relationship with microbial characteristics than the total heavy metals. This indicated theparticularity of urban ecology and environment. The microbial biomass and Cmic/Corg may be used as sensitive indexes for the urban environment change.The partitioning of heavy metals vary with different soil fractions and elements in urban zones. The fractions smaller than 0.002mm have the highest capacity to enrich heavy metals, while the heavy metals are obviously depleted in the fraction of 0.25-0.02mm.In addition,it seens Pb have the trend to enrich in the fraction of 2-0.25mm.The content of heavy metal is found the highest in the inner commercial and inner residence.lt seems the smaller fractions are the most sensitive to the urban environment and strongly influence human health.