典型山核桃产区土壤重金属空间异质性及其风险评价

山核桃(Carya cathayensis)是我国特有的高档干果和木本油料植物,目前关于山核桃林地土壤重金属污染研究鲜有报道.本研究以典型山核桃产区临安为研究区,系统采集了188个山核桃土壤样品,采用地统计学以及Moran's I等空间分析方法研究土壤重金属的空间异质性,并对山核桃林土壤重金属潜在生态风险进行评价.结果表明,重金属Cd、Cu、Zn、Pb、Ni、Cr平均含量分别为0.37、40.76、87.61、30.10、28.33、56.57 mg·kg-1,其中Cd、Cu平均值分别是背景值的1.33和2.87倍.单因子污染指数、内梅罗污染指数及潜在生态风险评价结果显示研究区土壤重金属均有样点超过土壤背景值,且Cd、Cu、Zn、Pb、Ni有部分样点超过土壤环境质量二级标准,表明研究区土壤已具有Cd、Cu、Zn、Pb、Ni、Cr不同程度的累积特征,局部土壤已受到Cd、Cu、Zn、Pb、Ni的污染,其中Cd最为严重,达到了强生态危害程度,Cu次之,总体上重金属呈中等生态危害程度.基于半方差函数分析得出,Cd、Cu、Pb、Ni、Cr具有强烈的空间自相关,而Zn属于中等空间相关性.Moran's I指数以及克里格插值结果揭示重金属Cd、Cu、Zn、Pb、Ni、Cr均存在明显的空间分布格局和局部空间聚集现象,高值主要集中在太阳、岛石、清凉峰、河桥以及湍口几个乡镇,且以重金属Cd、Cu污染风险概率较高.土壤Cd、Cu、Zn、Ni、Cr高值分布主要与矿区开采有关,而Pb与钾肥的施用密切相关.可见,研究区重金属空间分布特征受人为活动影响明显.

Spatial Variation of Heavy Metals in Soils and Its Ecological Risk Evaluation in a Typical Carya cathayensis Production Area

In recent years, the problem of soil pollution has become more and more serious. The problem of soil heavy metal pollution and its related human health risks has become a hot spot at home and abroad. Carya cathayensis is a unique high-grade woody nut and oil tree from China, and there are few reports on heavy metal pollution in Carya cathayensis plantation soils. Therefore, in order to study the spatial variability of heavy metals and the risk of pollution in Carya cathayensis soil and to promote the sustainable development of the Carya cathayensis industry, Lin''an, a typical Carya cathayensis plantation area, was selected for this study. A total of 188 soil samples were collected from the study area. We systematically studied the spatial heterogeneity of soil heavy metal content in the study area based on GIS technology, geostatistics, Moran''s I, and other spatial analysis methods. The single factor pollution index method, the Nemerow comprehensive pollution index method, and the potential ecological risk assessment method were used to evaluate the heavy metal pollution in the study area. The results indicated that the mean content of soil cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and chromium (Cr) were 0.37, 40.76, 87.61, 30.10, 28.33, 56.57 mg·kg^-1, respectively. The average values of Cd and Cu were 1.33 and 2.87 times of the background values, respectively, and the average content of other heavy metals did not exceed the background values. The results of the single factor Nemerow pollution index and potential ecological risk assessment methods showed that heavy metals in the study area exceeded the soil background values in some samples, and the second grade standard of soil environmental quality was exceed for Cd, Cu, Zn, Pb, and Ni in 31.38%, 31.38%, 2.65%, 0.53%, and 17.02% of the samples, respectively. This indicated that the soils in the study area had different accumulation characteristics for Cd, Cu, Zn, Pb, Ni, and Cr, and the local soil had reached pollution levels for Cd, Cu, Zn, Pb, and Ni. Among them, Cd was the most serious, reaching the degree of strong ecological damage, followed by Cu. In general, the heavy metal contents indicated a moderate degree of ecological damage. Based on the analysis of the semi-variance function, the Cd, Cu, and Ni in the soil were best fit with exponential models, the Zn and Pb were better fit with the Gaussian model, and Cr was consistent with the spherical model. Cd, Cu, Pb, Ni, and Cr had the strong spatial autocorrelation, with Nugget/Sill ratios of 12.1%, 4.6%, 14.9%, 2.6%, and 11.2%, respectively, while the Nugget/Sill ratio of Zn was 48.8%, indicating a medium spatial autocorrelation. Moran''s I and Kriging interpolation results found that the heavy metals Cd, Cu, Zn, Pb, Ni, and Cr all had obvious spatial distribution patterns and local spatial aggregation phenomena. The high values of heavy metals in soils were mainly found in Taiyang, Daoshi, Qingliangfeng, Heqiao, and Tuankou, and the probability of the risk for contamination by Cd and Cu was higher in the study area. The high values of Cd, Cu, Zn, Ni, and Cr were mainly related to mining, while Pb was closely related to the application of potassium.