北京市不同土地利用类型的土壤镉含量特征

Cadmium accumulation in soils for different land uses 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595个土壤样品的调查分析,探讨了不同土地利用方式对土壤镉含量的影响。结果表明,绿化地、麦地以及自然土壤与背景值没有显著差别;菜地、稻田、果园的镉含量显著高于背景值。6种土地利用类型中,菜地土壤的镉含量最高,其次为稻田和果园,绿化地以及麦地土壤镉的含量最低。与土壤基线值相比,果园样品有9.5%的样品超出,绿化地与菜地分别有7.7%和4.6%超出。在全部土壤样品中,共有19个样品超标,超标率为3.2%。石景山、门头沟、丰台、海淀等地区的样品超标较多,应该合理规划这些地区的农业土地利用。

Information on the environmental effects of different land uses is lacking, especially in Beijing, a city with a rapidly increasing rate of development. Such information is important for the understanding of the sustainable development and regional agricultural plans. In this study, through the investigation of 6 types of land use in Beijing, including vegetable field, paddy field, orchard, greenbelt, cornfield, and natural soil, Cd concentrations of 595 soil samples were obtained. Compared with background concentration, the accumulation of Cd in the vegetable field, paddy field, and orchard was significant. ANOVA analysis indicated that land use greatly affected the accumulation of Cd in the soils, especially in the cornfield, vegetable field, and orchard land-use types. The mean Cd concentration in the vegetable field was the highest, while samples from greenbelt and cornfield had the lowest mean concentrations. In addition, Cd concentrations of cornfield samples,which comprised the majority of samples under investigation, were low. Factors such as atmospheric deposition, which controls the large-scale distribution of Cd, might not have an obvious effect. Using a baseline concentration as background, the ratio of soil samples above this limit in orchard, greenbelt, and vegetable field were 9. 5 %, 7.7 %, and 4.6 %,respectively, while the overall ratio for the study was 3. 2%. According to this investigation, some anthropogenic factors such as industrial activities, traffic, and landfill waste,played quite important roles in the accumulation of soil sample Cd. The soil environment around the landfill, therefore, should be considered seriously. In the Shijingshan, Mentougou and Fengtai districts, the ratios of soil samples above baseline were much higher than those in other districts, and therefore reasonable planning of land use in these areas should be considered. According to the mean concentrations of Cd in the soil, the order of the 6 land-use types, from the highest to the lowest Cd concentration, was vegetable field paddy field orchard〉 natural soil〉 cornfield〉 greenbelt.