陕西泾惠渠灌区土壤重金属空间分布特征及来源

土壤重金属空间变异性是监测和评价农田生态系统环境质量的前提。该文基于104个表层土壤样品的重金属实测含量,运用多元统计和地统计相结合的方法,对陕西泾惠渠灌区土壤重金属含量的分布特征和来源进行了分析。结果表明,土壤中Hg、As、Cd、Cr、Pb、Cu、Zn、Ni 8种重金属平均质量分数分别为0.091、15.40、0.25、75.50、27.20、28.10、81.10、36.60 mg/kg,均超出土壤背景值(参考1986年报道的陕西省关中平原主要农业土壤中重金属含量),但低于国家土壤环境质量二级标准(GB15618-1995)。地统计分析表明,Hg、Ni、As基底效应介于25%~75%之间,属于中等空间相关;而Zn、Pb、Cd、Cu、Cr基底效应均大于75%,属于空间弱相关。多元统计分析表明,泾惠渠灌区土壤中Cd、Pb、Zn、Cu、As、Cr和Ni的累积主要源于农业生产活动、交通运输等人为活动,而Hg的累积则主要受工业排废的影响。目前,该灌区土壤环境质量良好,但土壤重金属有累积的倾向,应引起重视。

Spatial distribution and sources of heavy metals in soils of Jinghui Irrigated Area of Shaanxi, China

Abstract: With intense industrialization and urbanization, soil heavy metal pollution in some areas of China has become a serious environmental problem, and draws great attention because of its potential threat to food safety and detrimental effects on the ecosystem. Jinghui irrigated area of Shaanxi (China) is a main grain production area and has a pivotal position in Chinese agricultural development. With the growing development of irrigated area, large numbers of agricultural pollutants, traffic exhaust and industrial wastes are released into the environment, probably leading to heavy metal pollution in soil. The accurate assessment of soil quality in the irrigated area is important for the reasonable use of soil resources, which has important theoretical and practical value for the maintenance of agro-ecosystem productivity. In this study, a total of 104 soil samples at depth 0-20 cm were collected (one sample per 3 km×3 km), and the content of eight heavy metals (including mercury, arsenic, cadmium, chromium, lead, copper, zinc and nickel) in samples was analyzed to assess their geo-spatial distribution in soil of Jinghui irrigated area. Multivariate statistics (Correlation analysis, principal component analysis and cluster analysis) and geostatistics methods (ArcGIS tools) were used to identify possible pollution sources of heavy metals. The results showed that the content of the Hg, As, Cd, Cr, Pb, Cu, Zn and Ni in soil of the study area averaged 0.091, 15.4, 0.25, 74.4, 27.2, 28.1, 81.1 and 36.6 mg kg-1, respectively. All of them were slightly higher than their corresponding natural background values of agricultural surface soil in Shaanxi reported in 1986, but below the threshold values of the National Environment Quality Standard for Soil (GB15618-1995). Geostatistical analysis showed that the spatial variability and structure were good with varying nugget-to-sill ratio. The nugget-to-sill ratio of Hg, Ni and As ranged from 25% to 75%, indicating the moderate spatial dependence among them. The nugget-to-sill ratio of Zn, Pb, Cd, Cu and Cr were all higher than 75%, indicating weak spatial correlations. Spatial distribution maps showed the similar characteristics behavior for Pb-Cu-Zn-Ni, and heavy metal content was high mainly in Jingyang county, Sanyuan county and Yanliang district. Multivariate analyses suggested that the Hg, Cd, Pb, Zn, Cu, As, Cr and Ni in soils may be mainly derived from anthropogenic activities. Principal component analysis coupled with cluster analysis revealed that the tested 8 heavy metals were mostly from three sources. Pb, Cu, and Zn were associated with transportation, Cr, As, Ni, and Cd came up with agricultural practices, while Hg was closely affected by industrial discharge. Soil environmental quality of Jinghui irrigated area remained good at present, but had a trend of increase towards heavy metal accumulation. Therefore, a comprehensive environmental management strategy should be strengthened in this area.