Abstract:

To study the spatial distribution characteristics of soil heavy metals in suburb cropland of Changsha city，the buffer analysis and geostatistical analysis model were used to study the spatial variability characteristics of soil heavy metal contents （Cd and Pb）.Singlefactor assessment method was used to evaluate the quality status of Pb and Cd.While Hakanson method was used to assess the potential ecological risk degree.The results showed that the concentrations of Pb and Cd in largely sampling sites were at class I (below their average background values).There were some accumulations of Pb and Cd in soils,and the degree of accumulation of Cd was more serious than Pb.The average concentration of Pb and Cd in soils decreased with the distance in the buffer area at 3 ranges (i.e.less than 20 km,20 to 40 km and 40 to 60 km from urban area,respectively).It indicated that anthropic activity in urban has great influence on the concentrations of soil Pb and Cd in suburb cropland at certain spatial scale.The semivariograms of geostatistics analysis indicated the largescale spatial autocorrelations for soil Pb and Cd.The spatial autocorrelation and random both contributed to the spatial structure of soil Pb and Cd.The results of single accumulation index and potential ecological hazard coefficient of soil Pb and Cd showed the tendency that near suburban area was more serious than middle suburban area and distant suburban area,while distant suburban area was more serious than middle suburban area.The potential ecological hazard tendency of heavy metal Cd was more serious than Pb in each area.The accumulation extent and pollution risk outstanding area was on southnorth of near suburban and local industrial mining area of distant suburban