北京耕作土壤重金属含量的空间自相关分析

Spatial autocorrelation analysis of heavy metals in cultivated soils in Beijing

以北京市耕作土壤中重金属元素为例,采用Moran’s I统计量研究了土壤重金属含量的空间自相关关系、空间相关尺度以及空间分布规律.结果表明:北京市耕作土壤中8种重金属含量均存在空间自相关性.Cr、Ni、Zn、Hg、Cu、Pb、As、Cd的空间自相关尺度分别为57、75、57、55、55、65、74、37km.以Cr和Hg为例,用区域空间自相关指标结合Moran散点图分析了重金属含量空间聚集区和空间孤立区在研究区内的分布规律,其中"高-高"空间聚集和"低-高"空间孤立区域存在潜在的污染风险,对土壤重金属环境质量评价和重金属污染防治有着重要的作用.

Moran＇ s I statistics was applied to describe the spatial autocorrelation coefficients, correlation distance and spatial pattern of heavy metals in cultivated soils in Beijing. Significant spatial autocorrelations were detected for 8 heavy metals and the autocorrelation distances were： Cr, 57 ; Ni, 75; Zn, 57 ; Hg, 55 ; Cu, 55 ; Pb, 65 ; As, 74 km; and Cd, 37 kin. Local Moran＇s I was used to analyze the spatial distribution pattern of the heavy metals and identify the spatial clusters and spatial outliers. Taking Cr and Hg as examples, clusters of high-high Cr were observed in northeast Beijing （ Miyun county, Huairou and Pinggu districts） and in the Changping, Mentougou and Tongzhou districts. Clusters of low-low Cr were identified in the Fangshan, Daxing and Shunyi districts. Clusters of high-high Hg were distributed in the urban fringe. Outliers of low-high were found near clusters of high-high and outliers of high-low near clusters of low-low. The spatial distribution of heavy metals, particularly clusters of high-high and outliers of low-high which have potential pollution risks, play a key role in the assessment of the environmental quality of soils.