北京农田生态系统土壤重金属元素的生态风险评价

Ecological risk assessments of heavy metals in soils of the farmland ecosystem of Beijing,CHina

2005—2006年期间,分别采集了北京农田生态系统的大气干湿沉降、灌溉水和化肥3种外源输入的样品,共计63件。3种来源样品的年输入通量的定量计算和对比表明,不同地区不同输入途径的重金属元素的年输入通量差异较大,研究区农田土壤中重金属元素的主要输入途径是大气干湿沉降。如果不考虑农田生态系统的外源输出量,按照目前的污染速度,50年后怀柔和大兴地区表层土壤中Cd的含量可突破国家土壤环境质量碱性土壤的二级标准,污染情况比较严重,应引起足够的重视。其他地区的外源输入在相当长的一段时间内不会引起表层土壤重金属元素的含量发生质的变化。

From 2005 to 2006, 63 allochthonous samples were collected from the farmland ecosystem of Beijing. These samples include atmospheric wet and dry deposition, irrigation water and chemical fertilizers. Quantitative calculation and correlation of the annual input fluxes of heavy metals from the above-mentioned three allochthonous sources indicated that the annual input fluxes of heavy metals from different ways and areas are markedly different. The main input way of heavy metals in soils of farmland in the study area is wet and dry atmospheric deposition. According to the present accumulation rate of heavy metals, the concentration of Cd in soils of farmland in the Daxing and Huairou districts will excess the level of the State Soil .Environmental Quality Category Ⅱ in 50 years if the output fluxes from the farmland ecosystem is not considered. So enough attention should be paid to such a serious pollution situation. The input from external sources in other areas will not cause qualitative change in heavy metal concentration in soils in a quite long period of time.