Characteristics Of Soil Heavy Metal Pollution And Efficiency Of Phytoremediation Using Poplars In The Southern Beijing

This dissertation chooses the southern part of Beijing for its research area. By means of data processing, field investigation, laboratory analysis and stimulating experiment , it deals with the characteristics of the soil heavy metal pollution and the efficiency of phytoremidation using the poplar species. The contents of soil heavy metals decrease from the inner suburb to the outer one. They also decrease gradually with the zonal distribution from east to west in the area. Furthermore, there is a similar distribution from the centers of rivers or highways to their outside. In the soil profile, the heavy metals concentrate in the upper horizon, especially the 0~30cm horizon. The descending order for the contents of five heavy metals in soils is Zn, Pb, Cu, As and Cd . Most of the soil heavy metals, which exceed their background value, reach the pollution alarming level, as light pollution, medium pollution and heavy pollution respectively. The fates of soil heavy metals consist of exchangeable, residual, Fe-Mn redox extracted, carbonate extracted and organic extracted fractions. The contents and fates of sewage and sludge heavy metals are different form those in the soils. The contents of heavy metals in poplar tissues are different. The descending order for Pb content is leaf, shoot surface, stem surface, root surface, shoot, root and stem. The descending order for Cd is leaf, shoot surface, root surface, root, stem surface, shoot and stem. The descending order for Cu is shoot surface, shoot, leaf, root, root surface, stem surface and stem. The descending order for As is stem surface, root, shoot surface, root surface, stem, shoot and leaf. The descending order for Zn is stem surface, root, shoot surface, root surface, stem, shoot and leaf. The total heavy metals storage in poplar trees are quite different, the descending order is Zn, As, Cu, Cd and Pb. If soil is contaminated only by the Pb element, it needs much higher energy to absorb Pb. When the Pb element exists with Cd and Zn, the soil can absorb Pb with lower energy, and the absorption value Xm is high. According to the experiment data, the descending order for the desorption rates is Zn, Cd and Pb. This order shows that...