北京市不同土地利用方式下土壤铅的积累

Lead Accumulation in Soils under Different Land Use Types in Beijing City

通过对北京市菜地、稻田、果园、绿化地、麦地以及自然土壤等土地利用类型600个土壤的监测分析,探讨了不同土地利用方式对土壤铅积累的影响。研究结果表明,全部土壤样品中铅浓度的几何平均值为26.6mg/kg,显著高于北京市土壤背景值(24.6mg/kg),呈现出明显的积累趋势。不同土地利用方式对土壤铅积累有明显影响,其中绿化地土壤的平均铅浓度最高,依次为果园、菜地、稻田、自然土壤,麦地平均铅浓度最低,绿化地土壤的铅浓度要显著高于除果园外的其他土地利用类型。果园土壤的铅浓度同样与其他大多数土地利用类型的土壤有较显著的差别。以基线值为标准,除自然土壤外,其他5种土地利用类型下均有不同程度的样品超标:果园超标率最高(21.4%),其他分别为绿化地18.2%,菜地11.1%,稻田8.3%,麦地5.2%;样品总体的超标率为7.2%。从行政区域来看,城区土壤的铅浓度高于近郊区,近郊区要明显高于远郊区土壤,超标样点主要分布在昌平、朝阳、大兴、丰台、海淀、石景山区等城区或近郊区,因而土壤铅浓度有从城市中心区向外逐渐降低的趋势。在本研究中,大气沉降、垃圾填埋以及农药施用等人类活动可能是影响不同土地利用类型下土壤铅积累浓度的重要原因。

To obtain an overview of land use effects on the accumulation of Pb in the soil, 600 samples were collected from Beijing. The results showed that the geometric mean of all soil samples was 26.6 mg/kg, significantly higher than the background concentration of Beijing soil （24.6 mg/kg）. Based on the assessment compared with background concentration, increasing of Pb was found to be the highest in greenbelt and orchard and to a somewhat lesser extent in vegetable field and paddy field, whereas anthropogenic input seemed to be less important in natural soil. And the concentrations of Pb in greenbelt and orchard were significantly higher than those in other land use types. Using baseline as the criterion, the orchard showed the highest ratio beyond the limit for 21.4%. Corresponding values of greenbelt, vegetable field, paddy field, and cornfield were 18.2%, 11.1%, 8.3% and 5.2%, respectively and 7.2% for the total samples. The samples over the limit were mainly distributed in districts of Changping, Chaoyang, Daxing, Fengtai, Haidian and Shijingshan. The six districts were attributed with high ratios beyond the baseline limit for soil samples. Therefore, the concentrations of Pb in the soils declined gradually with the increment of the distance of the soils from the city zone. Through present investigation, it was found that the impacts of human activities of atmospheric precipitation, landfill of waste and fertilizer application are probably the important reasons for Pb concentrations under different land-use types.