污染场地土壤重金属空间异常值识别及其点源效应的分离

由点源污染导致的土壤重金属空间异常值的分布及点源效应的大小将影响场地风险评估和修复方案的制定,进而影响场地的环境管理.以某典型重金属污染场地为研究区域,以表层土壤Cd含量为研究对象,引入稳健变异函数模型,并筛选出合适的变异函数模型,结合平尾化方法对表层土壤Cd含量空间异常值进行识别和处理,并有效地分离出点源效应.研究表明：研究区表层土壤Cd含量空间变异大且存在明显的空间异常值;CressieHawkins稳健变异函数更适用于对研究区表层土壤Cd含量半方差函数的估计,采用稳健变异函数和平尾化方法能够有效地识别空间异常值和分离点源效应,空间异常值主要分布在受人为活动影响较大的区块;由于准点过程导致的变异较大,分离出的点源效应解释了异常值点位表层土壤Cd含量的大部分.

Identification of Oufliers of Heavy Metals in Soil of a Contaminated Site and Separation of Point Source Effects.

Spatial distribution of outliers and magnitude of point source effects of heavy metals in soil caused by point source contamination will affect accuracy of the risk assessment and making of soil remediation schemes, and further envi- ronmental management of the contaminated site. A typical heavy metal contaminated site was selected for the study and Cd concentration in the topsoil was set as object. A robust variogram model was introduced to screen out a suitable variogram model. Outliers of Cd concentration in the topsoil were identified and processed and point source effects were effectively i- solated with the aid of the winsorization method. Results show that the spatial variation of Cd concentration in the topsoil is great with obvious outliers. The Cressie-Hawkins robust variogram is more suitable for estimation of semi-variogram of Cd content in the topsoil. The use of the robust variogram model in couple with the winsorizafion method can effectively identi- fy outliers and separate point source effects. The outliers are mainly distributed at the locations with significant human activity. As the quasi-point process often leads to great variation, the isolated point source effects can explain most of the Cd concentration in the topsoil of the sites of outliers.