基于GIS的白银区耕地耕层土壤重金属空间分异及污染评价

GIS-based spatial variability and pollution evaluation studies of heavy metal in arable layer of Baiyin District

为评估白银区耕地耕层土壤（0～20cm）的重金属污染，应用x射线荧光光谱仪（XRF-7000）对1070个土壤样品中cu、zn、Ni、Pb、As、cr、V、C08种重金属含量进行了测定，参照最新土壤环境质量标准（GBl5618-2008），使用单因子和内梅罗法并结合GIS手段分析耕层土壤重金属空间分布及污染程度等。结果表明：8种重金属平均污染程度由大到小为As、V、Pb、zn、cu、co、Ni、cr，平均变异程度顺序为Pb、cu、zn、Co、As、Cr、V、Ni，空间相关性大小顺序为zn、cu、As、Pb、Ni、Cr、V、Co；Cu、Pb的最佳拟合模型为Pentaspherical模型，zn、V为Gaussion模型，Ni、As为Exponential模型，Cr、Co为Circular模型；8种重金属中Cu、Zn、Pb、As表现出不同程度的污染，评价结果显示安全级、警戒级、轻污染、中污染和重污染分别占全区耕地面积的69．56％、23．88％、2．95％、2．55％和1．06％，受污染面积达到763．4hm。。

Baiyin District of Baiyin City, Gansu Province, China relies on agriculture and stoekbreeding enterprises to develop featured agriculture. The action can promote agricultural development which makes farmers＇ incomes growing. However, in fact, Baiyin District is located in a resource-based city. Industrial and mineral industries in- elude mining, metal smelting and eleetroplating are relatively developed. Cultivated land has been polluted to a cer- tain extent which affects the health of citizens. So, it is necessary to understand the status quo of the cultivated land pollution. At present, the heavy metal pollution research is mainly focused on the mechanism, prevention and cure, repair, pollution status quo and risk assessment, etc. Most studies use less data to do risk assessment that can not comprehensively analyze the situation of heavy metal pollutions. Therefore, the paper gathered 1 070 sampling points on arable layer soil and detect 8 kinds of heavy metals of it to enrich the data. Then, via GIS, the paper evaluated the pollution present situation of Baiyin District, providing a basis for heavy metal pollution control and agriculture dis- tribution. Heavy metal contents of Cu, Zn, Ni, Pb, As, Cr, V, Co were measured with handheld X-ray fluorescence spectrometry （X-MET7000）. And the spatial distribution data of heavy metals were obtained with Geostatistical an- alyst of ArcGIS9.3 and SPSS18.0. Meanwhile, combining with the newest soil environment quality standard （GB15618- 2008） and using single factor and Nemerow index method, comprehensive pollution index method, the analysis was carried out on soil heavy metal spatial distribution and pollution levels of cultivated land arable layer. Conclusions include the following three aspects ： descriptive statistics, spatial variation characters and spatial distri- bution. Descriptive statistics shows that the average pollution degrees of the 8 heavy metals are ranked from big to small order as follows ： As, V, Pb, Zn, Cu, Co, Ni, Cr, while the variation degrees of this 8 heavy metals as follows ： Pb, Cu, Zn, Co, As, Cr, V, Ni. Spatial variation characteristics of soil shows that the optimal fitting model for Cu, Pb is Pentaspherieal Model; for Zn, V is Gaussion Model; for Ni, As is Exponential Model; for Cr, Co is Circular Model. And the spatial correlation from big to small order is Zn, Cu, As, Pb, Ni, Cr, V, Co. Spatial distribution maps of soil heavy metal content show that Cu, Zn, Pb and As have obvious zonality distributions and distribute like islands, while Ni, Cr, V and Co have interlaced distributions. Finally, through the analysis of the pollution status and pollu- tion evaluation, the paper found that Baiyin District was contaminated by Cu, Zn, Pb and As. Contaminated farmland accounts for 6.56% of the total area, covers an area of 763.4 hm2, the alert level farmland may be polluted by daily human activities and contaminated farmland may be caused by heavy metal mining and sewage irrigation.