北京市城市发展中土壤重金属的空间分布

通过系统收集和梳理近10年来(2005—2014年)北京市城市土壤重金属浓度特征和分布，探讨了城市扩张带来的土壤环境质量变化及城市发展中土壤环境质量的时空变迁。结果表明，北京市城市土壤中重金属Cu、Pb、Zn和Cr平均浓度分别为31.39、31.76、87.88和57.90 mg/kg，显著高于相应的土壤重金属背景浓度(18.7、24.6、57.5和29.8 mg/kg，P=0.00)；土壤重金属Cd平均浓度为0.26 mg/kg，与背景浓度(0.119 mg/kg)无显著性差异(P=0.464)。从环线分布规律而言，城市土壤重金属由内环到外环逐渐降低，二环土壤主要为Cu、Zn和Pb污染，三、四和五环土壤主要为Cu、Zn和Cr污染。从功能区分析，北京市公园土壤重金属综合污染指数最大(2.27)，其次是居民区(1.96)、交通区(1.90)和文教区(1.87)；公园土壤Cu和Pb污染较重，居民区土壤Zn和Pb污染较重，交通区和文教区土壤污染主要为Zn和Cu。总体看来，重金属Cu、Zn、Pb和Cr是今后北京市土壤环境质量控制的重点，同时应重点关注北京市公园土壤重金属的积累。

Spatial Distribution of Heavy Metals in Soils during Urban Development of Beijing

The concentrations and distribution characteristics of heavy metals in Beijing city soils in 2005-2014 were collected and analyzed systematically, in order to explore the variations of soil quality generated by urban expansion and the space-time changes of soil environment under the urban development. The results indicated that the mean concentrations of Cu, Pb, Zn and Cr in soils in Beijing were 31.39, 31.76, 87.88 and 57.90 mg/kg, respectively, which were significantly higher than the corresponding background values (P=0.00). There was no significant difference between mean concentration and background value for Cd in soils in Beijing (P=0.464). The concentrations of heavy metals in loop lines of Beijing showed a decreasing trend from inside to outside. Accumulations of Cu, Zn, and Pb were found in 2nd Ring Road, while Cu, Zn, and Cr in 3rd, 4th, and 5th Ring Roads. As for functional zones, the highest synthetical pollution index was 2.27 in soils from parks, followed by residential area (1.96), traffic area (1.90) and institutes area (1.87). High concentrations of Cu and Pb were found in soils from Park, with higher Zn and Pb in resident area, and Zn and Cu in traffic area and institutes area. Therefore, accumulations of Cu, Zn, Pb and Cr in soils were urgent concerns in management of soil quality, and more attentions should be paid to the accumulations of heavy metals in soils from parks in Beijing.