南京城市土壤某些元素的富集特征及其对浅层地下水的影响

本研究以南京市的公园、校园绿地、道路绿地和郊区菜地等不同功能区的土壤为对象,对土壤的磷素和重金属以及一些土壤剖面点位的地下水组成进行了分析.研究发现城市土壤构成了区别于自然背景的某些元素(如磷和重金属)的地球化学垒,形成了明显的元素富集区域,其中磷素含量是背景土壤的数倍甚至十数倍,Pb含量也远高出背景土壤,60%以上样品达到中等污染程度以上.从磷素在剖面中的积累模式可以看出,城市土壤中磷含量最高的层次出现在表层以下的不同深度,说明土壤经历了不同的扰动过程,这意味着在城市发展过程中,土壤的性质遭受强烈的人为活动影响,元素在土壤中的分布形态可以指示不同的利用历史.质量改变后的土壤对地下水等环境产生影响,使地下水的组成发生改变,其中磷素含量直接受到土壤的影响,效区菜地地下水中硝态氮含量极高,而本研究尚未发现地下水中的重金属含量与土壤有显著相关.

ENRICHMENT OF SOME ELEMENTS IN URBAN SOILS OF NANJING AND ITS IMPACT ON GROUNDWATER

Soils in various function zones of Nanjing, such as green park, campus lawn, road side green belt and suburb vegetable garden, were studied, by focusing on the characteristics of phosphorus and heavy metals, as well as on the composition and quality of shallow groundwater. The results showed that urban soils formed a special geochemical barrier of some elements, especially for those life linked elements (such as P and Pb), which is different from the natural background condition. Among which phosphorus is enriched by several to decades of times and more than 60% of the samples also showed a medium pollution of lead. The highest content of phosphorus appeared at different depths below soil surface, depending on the site conditions and the past land use changes. The distribution patterns of phosphorus illustrated that urban soils had been strongly affected by human activities in different ways during urbanization process. The study also showed that urban soils have higher proportion of non residual speciation of heavy metals, which may lead to higher risk of toxicity compared to that of natural soils. Physically and chemically altered soils had caused an effect on groundwater quality by changing its composition and in which nitrate was extremely high in suburban vegetable garden, and phosphorus was directly correlated with soil phosphorus condition while so far no significant relation found for heavy metals between soil and groundwater.