典型区土壤重金属空间插值方法与污染评价

选择最优的空间插值方法对土壤重金属空间分布特征的反映和污染评价具有重要的意义.以湖北省恩施市典型区表层土壤重金属As和Cd为例,选取常用的反距离权重法(IDW)、径向基函数法(RBF)、局部多项式法(LPI)和普通克里格法(OK)进行空间插值,对比分析了不同插值方法的插值精度及结果差异.同时采用地累积指数和指示克里格法(IK)评价了土壤重金属污染状况.结果表明,不同插值方法对于同一种元素的预测误差相差较小,但对土壤重金属含量的空间分布特征存在明显差异,其中LPI法表现出明显的平滑效应,OK法次之,而IDW法和RBF法极大地保留了元素含量的极值信息,插值结果较详尽.为准确了解局部高背景区土壤重金属的空间分布状况,应优选IDW法或RBF法进行插值.以湖北省深层土壤重金属含量算术均值作为背景值,地累积指数污染评价结果显示:As和Cd的超标样点分别占5.5%和99.0%,研究区Cd污染程度较高.IK法污染评价显示:Cd中度-强污染以上的高概率污染区域主要位于研究区的中部,应重视土壤Cd污染分布,并对其有效治理与修复.

Spatial Interpolation Methods and Pollution Assessment of Heavy Metals of Soil in Typical Areas

It is important to choose the best spatial interpolation method to reflect spatial distribution features and evaluate soil heavy metal pollution. The spatial distribution of arsenic (As) and cadmium (Cd) concentrations in top soil samples from Hubei Province were studied by four frequently-used spatial interpolation methods, including inverse distance weighted (IDW), radial basis function (RBF), local polynomial interpolation (LPI) and ordinary kriging (OK). The interpolation precision and effect of the spatial distribution of the four methods were compared with the results of cross validation and spatial distribution, and the pollution was assessed by the geoaccumulative index (I_geo) and indicator kriging (IK). The results showed that the four interpolation methods had small prediction errors, but that the interpolation effects were quite different. Among them, LPI had the most serious smoothing effect, followed by OK. The IDW and RBF best retained the extreme value information for element concentrations, and interpolation results were more detailed-and so to accurately understand the distribution of soil heavy metals, IDW or RBF methods were recommended. Taking the arithmetic mean of heavy metal concentrations in deep soil of Hubei Province as the background value, the evaluation result of geo-cumulative index pollution allowed exceedance percentages for As and Cd accounted for 5.5% and 99.0% respectively. The soils of the study areas were heavily contaminated with Cd. The pollution evaluation result from IK showed that high probability contaminated areas, with moderate-heavy contamination levels, were mainly located in the central part of the study area. The authors concluded that development of agriculture in the research area should include attention to Cd pollution and that soils there required the effective treatment and restoration of Cd levels.