Spatial Distribution Of Heavy Metals In Urban Forestry Soil Based On GIS

Urban forest soil is an important part of the urban environment, with the rapid development of industry, increasing the vehicle in the city, urban expansion brought about by the large construction projects, will lead to increasing pollution of heavy metals in Nanjing city. Nanjing is the capital city of Jiangsu Province, an important economic and cultural center study the heavy metal distribution and contamination, provide data reference and theoretical support for Nanjing city future development planning and land use. This experiment in Nanjing city using valid samples of 1km×1km grid sampling method to collect 180 soil samples, each sample within the grid is mixed soil samples, collected soil surface level is 0 ~ 15cm; Determination of copper(Cu), zinc(Zn), manganese(Mn), lead(Pb), cadmium(Cd), chromium(Cr) in soil use the method of HF-HNO3-HClO4 digestion—ICP; the sample points are classified according to their functional areas, select 18~24 sample points data for heavy metal content analysis from the data of each functional area; and basing on the difference and correlation analysis of heavy metals in soil by ArcGIS geographic information system and SPSS, researching the overall spatial distribution of heavy metal in the forestry soil of Nanjing City and distribution of different functional areas of heavy metal content, researching the source and the heavy metal and black carbon(BC) and the correlation and homology. The main results are as follows:(1) Through the ArcGIS to draw distribution map of the six kinds of heavy metals of forestry soil in Nanjing. The distribution chart, trend chart and data content analysis. The results show that: in Pb, Zn, Cd pollution is heavier; the average content of Mn and Cr did not exceed background value of soil of Nanjing, individual regional content is higher; distribution characteristics of urban commercial and cultural center of the Drum Tower- Xinjiekou area of heavy metals Cu, Zn, Mn, Pb, Cd, Cr were significantly island distribution, content were higher, and this area larger traffic flow and busy commercial activities, as the influence factors about; secondly, Yangtze River Bridge regional Cu, Zn, Mn, Cr content were higher, city north of the Yangtze River Bridge and the chemical plant area of heavy metal Cr pollution is obvious.(2) Through the study of soil heavy metals in different functional areas, the heavy metals in the commercial area, industrial area, and traffic green belt are up to a higher level, and the characteristics and functions of these functional areas are closely linked. Among them, the Cu, Zn, Mn, Cd, Cr content in the business district is the highest, and the content of Cr in the industrial zone is the highest.(3) Through the correlation analysis between the heavy metal and the black carbon content, we can know that each other show extremely significant correlation between Cu, Zn and Mn in the urban forestry soil of Nanjing; Pb-Zn, Cu-Cd, Cu-Cr, Zn-Cr, BC-Zn, BC-Pb show extremely significant correlation, but correlation coefficients were low; BC-Cu, Cr-Mn are significantly correlated; Zn and Cu, Zn and Pb, Cu and Cd have a certain degree of homology,Cu and Pb has other different sources; BC and Cu, BC and Pb have certain homology; BC and Cr have no significant correlation and they are from different sources.