渭北黄土高原苹果园土壤重金属空间分布及其累积性评价

通过对渭北黄土高原苹果园217个样点0～40cm土层土壤取样分析,采用地统计学和GIS相结合的方法,研究了苹果园土壤中Hg、Cd、Pb、As、Cr、Cu6种重金属的含量及其积累状况、空间结构及其分布特征,并根据绿色食品产地环境质量标准对苹果园土壤环境质量进行了评价。结果显示,渭北苹果园土壤中6种重金属已出现一定程度的累积,其累积程度依次为：Hg〉Pb〉Cd〉As〉Cu〉Cr。各采样点Hg、Cd含量变异程度较大,变异系数在50%以上;而Pb、As、Cr、Cu各采样点含量差异较小,变异系数为19.10%～23.70%。6种重金属均表现为较强的空间相关性,其空间变异性主要由成土母质、气候、地形等结构性因素控制。其中随机因素对Cd的空间变异的影响程度相对较大,一定程度上消弱了结构性因素对Cd空间变异的主导作用,而Pb、Cr、Cu空间变异受随机因素的影响较弱,随机性因素对各重金属空间变异的影响程度依次为：Cd〉As〉Hg〉Pb〉Cr〉Cu。重金属积累的单项评价指数均小于1,综合评价指数小于0.7,果园土壤环境质量完全满足绿色食品产地环境质量的要求,其中As的累积对绿色食品苹果生产可能有较大的潜在影响,应加以有效控制以防止其持续累积。

Spatial Distribution and Cumulation Evaluation of Soil Heavy Metals in Apple Orchards of Weibei Area, the Loess Plateau

From the apple orchards in the Weibei area of the southern Loess Plateau of China, 217 surface soil samples of 0-40cm layer soll were collected to analysis the spatial distribution of 6 heavy metals（Hg, Cd, Pb, As, Cr and Cu ） with the help of geo-statistical method and GIS technology. Simultaneously, soil environmental quality was evaluated according to the environmental quality standards of green food production base by methods of both the single factor and the Nemerow multi-factor. The results indicate that the content of these 6 metals are cumulated in the studied apple orchards, especially the element of Hg and Pb, when compared with the corresponding natural background values. However, the soil environmental hazards to these 6 metals are little currently. Coefficient of variation of Hg and Cd are more than 50% and higher than that of Pb, As, Cr and Cu. Distribution of these 6 heavy metals present a stronger spatial relevance because their spatial pat- tern are mainly influenced by natural factors such as the soil parent material, climate, topography and other structural factors. Random factors play a relatively greater role in spatial variability of Cd than others listed as Cd 〉 As 〉 Hg 〉 Ph 〉 Cr 〉 Cu. Single factor index of all metals are less than 1 and their multi-factor index are less than 0.7, it shows that the studied apple orchards meet the needs of the green food production base for further development. On the other hand, the content of As may have a potential negative influence to the green food production, therefore, real-time monitoring and protection measures are required to prevent its further enrichment.