北京市不同土地利用类型的土壤砷含量特征

Arsenic accumulation in soils for different land use types in Beijing

通过对北京市菜地、稻田、果园、绿化地、麦地以及自然土壤6种土地利用类型共500 个土壤样品的调查分析,探讨了不同土地利用方式对土壤砷积累的影响。与北京市土壤背景值相比,砷在土壤中均有不同程度的增加,累积现象比较普遍。在6种土地利用类型中,自然土壤的砷含量最低,最接近背景值;菜地和稻田的土壤砷含量的增加最为显著。以基线值为标准,北京市涉及土地利用的土壤砷含量总体超标率为1.8%;6种土地利用类型中,菜地、果园、麦地三种土壤砷含量的超标率分别为2.6%、2.7%、0.7%。土壤砷含量的平均值由高到低分别为:稻田>绿化地>菜地>果园>麦地>自然土壤。

Differences in land use and land cover comprise a complicated process, which involves conversion of the natural soil ecosystem to an artificial ecosystem. This process may affect the accumulation of heavy metals in soils. The knowledge of the heavy metal concentrations for different land use types, which has been infrequently investigated, is of critical importance to assess human impact on heavy metal concentration in soils. Arsenic is a toxic heavy metal with an ADI (acceptable daily intake) of 2. 14 jug/kg body b. w. / day, according to the WHO. In this study, 500 samples were collected from 6 land-use types, including vegetable plot, paddy field, orchard, greenbelt, wheatfield, and natural soil, to compare differences between As concentrations of these soil-use types in Beijing. In comparison with background, the concentrations of As in the different land-use types increased to different extents. The accumulation of As in soils was widespread. Through ANOVA analysis, it was found that land-use type obviously influenced soil As concentrations. The natural soil type had the lowest concentration of As. The vegetable and paddy fields had the greatest concentrations of As. The intensity of anthropogenic activities, such as the use of pesticides, chemical fertilizers, and fuel combustion, was identified as an important factor affecting the concentration of As in soils. Using a baseline concentration as a reference, the ratio of all soil samples above this limit was 1. 8%, among which the ratios of soil samples from vegetable plot, orchard, and wheatfield were 2. 6%, 2. 7%, and 0. 7%, respectively. According to the mean concentrations of As, the order of the 6 land-use types, from the highest to the lowest As concentration, was paddy field > greenbelt > vegetable plot > orchard > wheatfield > natural soil. The environmental quality of paddy field and vegetable plot soils needs to be closely considered because of the high accumulation of As in these soil-use types.