田块尺度污染农田土壤铅、镉和砷含量的空间变异及其对土地利用的启示

Field-scale Spatial Variation of Pb, Cd and As in Contaminated Farmland Soils and its Implication for the Utilization of the Farmland

为了探明铅冶炼污染区田块尺度下农田土壤重金属含量的空间变异及其对污染农田土壤安全利用的意义,在某冶炼厂附近一面积为4800 m2的农田用网格法采集120个0~20 cm土样,测定样品镉、铅和砷含量。研究表明,研究区土壤中存在砷、镉和铅的积累。从平均污染指数来看,以镉的积累程度最大,铅次之、砷最小。土壤全镉含量的变化范围为1.10~3.84 mg kg^-1,镉含量处于1.10~2.27 mg kg^-1之间的样品占97.50%。从重金属空间分布上看,镉和铅含量的空间分布有较高的一致性,均是研究区北部和南部含量较高,中间区域含量较低。相关分析表明,土壤镉和铅含量之间存在显著正相关(P <0.01)。根据土壤铅含量计算稳定铅时所用普通过磷酸钙的用量范围为0.312~0.419 kg m^-2,平均值为0.367 kg m^-2。根据其他研究者得到的土壤全镉含量与小麦籽粒镉含量的相关方程计算,不同方程得到的小麦籽粒镉含量结果有很大差异,较可信的小麦籽粒镉含量变化范围为0.095~0.814 mg kg^-1。采样区中部为小麦籽粒镉含量较低且铅稳定剂需要量较低区域。以上结果表明,研究区田块尺度下土壤镉含量存在较大的空间变异,且土壤镉含量的空间变异导致小麦籽粒镉含量可能存在较大的空间变异。

In order to investigate field-scale spatial variation of heavy metals in farmland soils near a lead smelter,120 soil samples were collected from 0-20 cm depth of a 4800 m^2 farmland field by a grid method and were analyzed for Cd, Pb and As. The results showed that As, Cd and Pb were accumulated in the soil following the order of Cd > Pb > As. The Cd concentrations ranged 1.10-3.84 mg kg^-1, and 97.5% of soil samples had Cd concentrations of 1.10-2.274 mg kg^-1. The spatial distributions of Cd and Pb were more similar than that of As, with higher concentrations in the northern and southern field, but lower in the middle field. Significant correlation(P <0.01) existed between the concentrations of Cd and Pb. The superphosphate dosages calculated by the Pb immobilization ranged 0.312-0.419(mean 0.367) kg m^-2. The estimated Cd concentrations in the wheat grain were substantially different among different equations from the published literatures, and the most reliable values ranged 0.095-0.814 mg kg^-1. The middle field had a lower Cd concentration of wheat grain and required a lower dosage of phosphate for Pb immobilization. All the results indicated that the spatial distribution of soil Cd concentration exists the large variation at field scale, which results in the large spatial variation of wheat grain Cd concentration.