Spatial Distribution Of Heavy Metals In Wuhan Peri-Urban Soils

Urban expansion, industrialization, as well as the development of agricultural intensification affects soil environmental quality. In particular the input of heavy metals in soil on soil can affect soil physical and chemical properties. They also harm human health throught water and air which contain heavy metal from soil.In urban soil there are lots of metals which from many kinds of sources, the study of distribution and sources of soil heavy metals can provide a theoretical basis to protect the ecological environment and construct suitable living environment in some sense.In this study, we use landscape fragmentation and diversity index (SHDI) theory to divide study area into three parts: urban, peri-urban interface and rural areas quantificationally. 112 samples are sampled in three places, 0-10cm, 10-20cm, 20-40cm, respectively. We analyse six heavy metals (Cd, Cu, Ni, Pb, Zn, Mn) and two conventional elements (Ca, Mg) in soil samples. Spatial analysis and Factor Analysis (FA) are done to interpret the spatial distribution of heavy metals. In this paper, the main conclusions as follows:(1) Spatial distribution of heavy metals. Firstly, the analysis of horizontal direction, descriptive statistics are carried out at three levels, there are not only comparisons with the national background values, but also comparisons between study areas. Results show that: heavy metal Cd exceeds 9 times of the national standard, Cu also exceed 50%, Ni, Pb, Zn, Mn content are the same as GB basically; soil heavy metal content in peri-urban interface is higher than urban and rural areas. Vertical analysis showed that: heavy metals in urban soil mainly centralize in 0-10cm, as peri-urban interface and rural areas, 10-20cm.(2) Spatial prediction analysis of heavy metals. Firstly original Data are carried out K-S normality test, as to the data of Non-normal distribution, log transformation is done. Then we compare errors between different interpolation methods, ordinary kriging(OK), inverse distance weighting method(IDW), RBF neural network(RBF), to decide the excellent interpolation method, the smaller the error, the better the method.The spatial prediction map of different metals in three levels are generated in ArcGIS. In the help of vertical analysis, we can come to the conclusion, six heavy metals mainly concentrated in the urban, but rarely in peri-urban interface and rural areas. Map shows, the distribution of heavy metals in level 0-10cm is very fragmented, and mainly located in peri-urban interface. The most obvious characteristic of heavy metals Cd, Cu, Ni, and Pb is there is a highest value in peri-urban interface, and they concentrate in three special regions.(3) Source analysis of heavy metals based on Factor Analysis. According to Celine's theory, in factor analysis, whether heavy metals and conventional elements are in the same common factor is often used to determine the source of heavy metals. In this study, factor analyses are carried out in three levels of three study areas, respectively. Results showed that: In City, heavy metals of level 0-10cm is mainly affected by traffic and life factors, which are primary human activities, the distribution of heavy metals in level 10-20cm and 20-30cm is determined by parent material, urban heavy metals accumulate on soil surface mainly.Whereas heavy metals in peri-urban interface soil surface can easily leach to 10-20cm, which has a higher value. We can explain the the effects of rain leaching on heavy metals in soil. Most of the samples in rural areas are collected from the badlands, and there is a trend that heavy metals in the soil transfer to rhizosphere slowly, so the Man-made sources of heavy metals in soil layer 1 of is not very clear, but heavy metals in soil 2 are significantly increased, which can be seen in vertical analysis; as a result of sample depth, heavy metals in layer 3 reflects good original.