南京市历史文化层中土壤重金属元素的分布规律初探

DISTRIBUTION OF HEAVY METALS IN CULTURAL LAYERS OF URBAN SOILS IN NANJING

文章对南京市城区不同地点出现的多个文化层中土壤的理化特征进行了系统研究。研究结果表明 ,文化层中土壤的重金属元素含量比南京市非城市土壤和背景平均值有增高的趋势 ,局部地段有巨量增高。从剖面纵向上看 (时间上 ) ,这种增高现象主要发生在近现代、明清和六朝 3个历史时期 ,这与历史上这些时期南京相对发达有关 ;而从横向地域上看 (空间上 ) ,重金属元素含量的分布明显可以分成两组 ,两个组分别代表了地域上的不同 ,如明故宫 -大行宫 -中山东路一带历史上许多时期是皇城区 ,而内秦淮河流域一带则可能是古代的手工业和制造业区、商贸区和普通大众的生活区 ,这种明显的差别揭示出南京在各历史时期上的城市功能区是各不相同的。磁化率特征研究结果表明文化层中土壤的磁化率在各历史时期分布是不同的 ,磁化率的高峰时期有近现代、清朝和明朝时期 ;频率磁化率特征研究结果表明磁性矿物主要是外源输入造成的。与此同时磁化率高峰时期基本上与重金属元素增高地段是一致的 ,这进一步印证了文化层中重金属元素增高主要是由于外源污染物质的输入造成的。

The contents of heavy metal and magnetic susceptibility of several cultural layers in Nanjing were measured. The results show that the contents of heavy metals in all cultural layers are higher than those of local suburban soils. It means that tremendous accumulation of heavy metal took place in some of historical dynasties, such as Qing, Ming and South Dynasties, as well as present day. The increase of heavy metal content in historical records reminds us of the development of hadicraft industry, manufacturing and business prosperity in those periods in Nanjing. The spatial distribution pattern of heavy metal content, all the sites can be divided into two groups, indicating their function difference. One of them was the place that royal quarter was located, for example, the area of Daxing Palace, royal center of Ming Dynasty. Another of them was the locality of manufacturing region, handicraft industry center, maybe the trade region and residential area also. These localities are located at the area near Qinhuai canal. The measurement of magnetic susceptibility indicates that the peak value appears at those localities with higher heavy metal contents, especially Qing, Ming dynasties and present day. The frequency dependent magnetic susceptibility indicates that the magnetic enhancement is caused by human activities. This means that either the increase of heavy metal content or the magnetic susceptibility is not natural process but man made process.