Spatial Distribution Analysis And Pollution Apprasial Of Heavy Metals Contents In Farmland Soil And Irrigation Water In Nantong City

The habitat environment will be the foundation of nuisanceless agricultural product production; the habitat environment has the direct influence to the quality and security of agricultural product. In this paper, according to the sample data of the farmland soil and the irrigation water in Nantong area, the spatial distribution of heavy metals contents in farmland soil and irrigation water was analyzed based on spatial analysis model and GIS. And based on the spatial analysis result, the heavy metal pollution of farmland soil and irrigation water was appraised and the early warning was proposed.The main tendency and results of the domestic and foreign research on the spatial analysis of heavy metals contents was summarized ,and the main contents and the technical route of this research was proposed in the first chapter. In the second chapter, The geographical location, climate and industry and agriculture of Nantong city was summarized, the sample design of farmland soil and irrigation water was introduced in detail, and the spatial analysis model of heavy metals contents in farmland soil and irrigation water was selected based on the spatial distribution of sample point. In the third chapter, according to the normal statistic results, the spatial variations of heavy metals contents in farmland soil were analyzed based on variograms. The artificial nerve network model and the GIS technology were carried on to the spatial interpolation of heavy metals contents in farmland soil in Nantong. In the fourth chapter, the spatial autocorrelation method was used to analyze the spatial distribution of the heavy metals contents in irrigation water in Nantong .In the fifth chapter, the heavy metal pollution of farmland soil and irrigation water was appraised and the early warning was proposed, based on the spatial analysis result. Finally, In the last chapter of this paper, the major findings were summarized and discussed, and other problems needing further studies were prospected. Through this paper, following conclusions were achieved: 1 The five kind heavy metals in farmland soil in Nantong city have different nugget. The nugget of Cr element (245.9) was the highest, and the nugget of Hg element (0.001420) was the lowest. Compared with structure variance, the nugget was small. It indicated that the sample distance of farmland soil was suitable. The nugget/sill ratios of Hg, As and Pb were less than 0.25, The nugget/sill ratios of Cd and Cr were between 0.25 and 0.75. The nugget/sill ratios of five kind heavy metals were less than 0.5. The stochastic spatial variation was less than the spatial variation which partially caused by the spatial autocorrelation. The result indicated that the heavy metals contents in farmland soil were mainly affected by the geological lithological character, soil type, climatic conditions and so on,2 A better result of the spatial interpolation of soil heavy metals contents has obtained based on ANN and GIS .According to the appraisal of the interpolation result, the most remarkable heavy metal pollution is Pb, the area which surpasses the background value is up to 68.24% of all. The next is As, the area which surpasses the background value is up to 23.02% of all. although, Other three kind heavy metals have the high gathering phenomenon in the local area, but the pollution area are smaller than Pb and As .The result of pollution appraisal indicated that there are some mild pollution area in Nantong urban district, Haimen city and Qidong city .The majority area of this three regions are in the security to limit, should give the high value to local farmland soil heavy metal contamination concern. In the east of hai'an and the juncture of western Tongzhou and Nantong, there are some small mild pollution area. The majority area of Rudong county and Rugao city do not have the pollution. Only in local area, there are some regions in the security to limit.3 In the irrigation water, Cu, Zn and Cr have significant negative correlation coefficients. Cu/Zn, Cu/Cr, Zn/Cd, Zn/Cr have significant positive correlation coefficients. The spatial correlation coefficient of Hg is the biggest in the seven kind heavy metals. As and Cd are next, Pb, Cr, Zn and Cu are the smallest. The result of spatial correlation analysis indicated that the distribution of Hg in irrigation water has significant spatial structure. The distribution of Pb, Cr, Zn and Cu haven't spatial structure and assumes random distribution. The distribution of As and Cd haven't significant spatial structure. The result of pollution appraisal indicated that the heavy metals contents in irrigation water are lower overall. Most areas can achieve the irrigation water quality standards, only in part area of Nantong urban district, Qidong city and Rudong County occurred heavy metal pollution of Cd, Cr and Cu.