污灌区土壤重金属空间结构与分布特征

Spatial structure and distribution characteristics of soil heavy metals in wastewater irrigation district

该文探讨了地统计学插值模型应用于土壤重金属污染评价的适用条件,分析了北野场污灌区土壤重金属的正态分布特征和主导分布趋势,提出了不同重金属因子适宜的地统计插值模型。结果表明:土壤重金属空间变异系数处于12%～37%之间,整体变异性不大;Pb、Cd等因子的块金效应分别为0.90、0.87,空间相关性较弱,受人为随机因素的影响较大,As、Cr、Zn、Cu值等因子的块金效应分别为0.52、0.51、0.51和0.46,空间相关性中等,受人为随机因素和空间结构因素的共同作用,Hg和Ni的块金效应分别为0.253和0.06,空间相关性较强,受空间结构性因素的影响较大,可能受原生地质的影响较大。污灌区重金属含量存在增加趋势,灌区土壤重金属含量自北向南总体呈现较少趋势,这与灌区上下游灌溉保证率不同有关,表明长期污水灌溉可导致土壤重金属富集,但与全国其他污灌区相比,北野场污灌区土壤重金属污染相对较轻,应加强污水处理利用避免土壤重金属污染。

Based on geostatistical methods and analysis module of ArcGIS, this paper discussed applicable conditions of Geostatistical interpolation for evaluating soil heavy metal pollution. Taken Bei Yechang wastewater irrigation district as research subject, the spatial distribution characteristics and global trends of heavy metals were analyzed in order to propose appropriate geostatistical interpolation models. The results showed that average heavy meal contents of As, Hg, Cd, Cr, Cu, Pb, Zn and Ni in Bei Yechang wastewater irrigation district were lower than the first class limit values of soil environment quality standard, and increased by 11.5%, 207.7%, 18.7%, 25%, 39.2% and 21.3% compared with soil background values. The contents of heavy metals varied from -4.6% to 10.4% compared with the same research in 1978. The spatial coefficient of variation varies from 12% to 37% with no significant spatial variation. By the histogram module of ArcGIS geostatistical analyst tool, Hg in soil was normally distributed; Cd approximately closed to the normal distributed by log transformation, while the contents of As, Cr, Cu, Pb, Zn, Ni were not normal distributed. Ordinal kriging interpolation model and Ordinal kriging interpolation model with log transformation were proper for the spatial interpolation for the content of Hg, Cd in Bei Yechang wastewater irrigation district, and universal kriging interpolation model were proper for the spatial interpolation for the content of Zn, Ni, while contents of the other facts in Bei Yechang wastewater irrigation district should choose the disjunctive kriging interpolation model. The nugget effects of Pb and Cd were 0.90 and 0.87 with weak spatial variation, respectively, indicating Pb and Cd were influenced by artificial random factors. The nugget effect values of As, Cr, Zn and Cu in Bei Yechang wastewater irrigation district were 0.52, 0.51, 0.51 and 0.46 with medium spatial variation, respectively, indicating As, Cr, Zn and Cu were influenced by the combined effects of artificial random factors and spatial structure. The nugget effect values of Hg and Ni were 0.253 and 0.06 with higher spatial correlation, respectively, indicating Hg and Ni were influenced by in structural factors and geology of the native. In the Bei Yechang wastewater irrigation district, compared with background values the heavy metal contents increased. Heavy metal contents decreased from north to south with irrigation guarantee rate decreasing along the main canal. The results indicated that long-term wastewater irrigation can lead to soil heavy metal enrichment. Compared with other irrigation districts in China, the pollution level of Bei Yechang wastewater irrigation district was slighter and wastewater should be treated to prevent soil heavy metal pollution.