北京南部地区农业土壤重金属分布特征与评价

包括通州、大兴、丰台和房山4区的北京南部地区的土壤存在不同程度的重金属污染。在该区域选取25个土壤样品，其中剖面JN1（JN表示北京南部地区土壤剖面，下同）按土壤发生层在春季（3月下旬）和秋季（11月上旬）采样，研究土壤Pb、Zn、Cu,Cd和As等元素时空分布特征及其污染程度。结果表明，该地区土壤重金属含量不等，由高到低依次为Zn、Pb、Cu、As和Cd，属于歧义性污染。区域内自东向西，土壤重金属含量逐渐减少，其中沿河流、高等级公路向两侧，土壤重金属含量由高到低。土壤重金属集中于土壤表层．Cd、Cu、Pb、Zn主要富集在0—20cm土层中，20cm以下深度的含量大大减小，土壤重金属元素含量春季高于秋季。土壤综合污染指数均大于1，处于轻污染以上水平。

Distribution and Evaluation of Heavy Metals in Agricultural Soil in Southern Area of Beijing

The southern area of Beijing includes Tongzhou, Daxing, Fengtai and Fangshan District. The soil in this area has been polluted by heavy metals. In order to prevent this area from further pollution and improve the agriculture product quality, it is imperative to study the heavy metals distribution and their pollution effects. Twenty-five soil samples are taken, and among these, the soil from JN1 profile is taken in the spring (the last ten days of March) and autumn (the first ten days of November) respectively. The distribution and pollution evaluation for Pb, Zn, Cu, Cd and As are mainly researched. The contents of heavy metals in the soils are different in this region, with the order in term of the content being Zn>Pb>Cu>As>Cd. From the east to the west in this area, the contents of soil heavy metals decrease gradually, and along the rivers and highways, the contents of soil heavy metals also decrease from the inside to the outside gradually. The heavy metals concentrate on the upper horizons, especially the 0~20 cm horizon in the soil profile, and decrease abruptly below the depth of 20 cm. The contents of soil heavy metals in the spring are higher than those in the autumn. All the heavy metal pollution indexes surplus 1.0, suggesting that the soils in this area are polluted by the heavy metals slightly.