万州老城区楼顶菜地土壤重金属污染特征

为研究万州老城区菜地土壤重金属污染状况，运用ArcGIS地统计分析模块分析了万州老城区楼顶菜地中5种重金属元素Cr，Cd，Cu，Ni和Mn的空间分布特征，并采用地累积指数法评价了楼顶菜地土壤中重金属的污染状况.结果表明:w(Cu)，w(Ni)和w(Mn)属于中等变异，w(Cr)和w(Cd)属于强变异，说明楼顶菜地重金属的来源受外界干扰明显，空间变异较大；在空间分布上，这5种重金属存在一个相同的高值区A，位于研究区西北部；w(Cr)，w(Ni)和w(Mn) 另一高值区在研究区中西部部分重合，表明Cr，Ni和Mn元素之间可能存在一定的复合污染，与相关性分析的结果一致；根据地累积指数法评价结果，万州老城区楼顶菜地土壤Cd为重度污染，Cr为轻度污染，Cu，Ni和Mn未受污染. 

Pollution Characteristics of Heavy Metals in Vegetable Garden Soils on the Roof of Buildings in the Old District of Wanzhou City

Spatial variation characteristics of heavy metals including Cr,Cd,Cu,Ni and Mn in vegetable garden soils on the roofs of buildings in the old district of Wanzhou city were studied using the ArcGIS geostatistical analytical module.The geo-accumulation index method was used to assess the heavy metal pollution status.Results showed that among the five elements,w(Cu),w(Ni) and w(Mn) were medium in variation intensity,while w(Cr) and w(Cd) had a big spans of variation,which suggested the sources of heavy metals in the vegetable garden soils were significantly affected by outside interference with a large spatial variability.In the spatial distribution,all of the five metals had the same hotspot A,which was located in the northwest of the study area.The concentrations of Cr,Ni and Mn showed some overlapped areas in another hotspot which was located in the midwest of the study area,indicating there may be some combined pollution.Correlative analysis also gave the same result.According to the results of the geo-accumulation index assessment,the soils were seriously polluted by Cd,slightly polluted by Cr,and unpolluted by Cu,Ni and Mn.