兰州城市土壤磁性特征及其对环境污染的指示

对兰州市城区117个表土样品和11个土壤剖面的磁学特征进行系统分析,结果表明:兰州市表土磁化率平均值为219.23×10-8m3/kg,低矫顽力的亚铁磁性矿物为主要载磁矿物.磁铁矿的高值主要集中在以下4个区域:(1)以兰州铝厂、西固火电厂为中心的工业区域;(2)以水上公园为中心的区域;(3)西北物资市场-西站-小西湖-西关-城关大桥沿线的狭长条带状区域;(4)以雁儿湾和兰东建材市场、皮革厂为中心的区域.对不同功能区而言,西固区和城关区磁性矿物浓度最高,安宁区磁性矿物浓度最低.土壤剖面结果显示,上部20cm,clf和SIRM显著升高;20cm以下,clf和SIRM稳定且较低,说明兰州市土壤污染的纵向迁移深度在20cm以内.兰州市表土、街道尘埃、大气降尘和河道沉积物相对无污染样品而言,都具有磁性矿物类型单一,以磁铁矿为主导的特征;并且都随着磁化率的升高,出现百分频率磁化率降低的趋势,显示出与无污染样品不同的特性.因此,运用环境磁学方法在城市环境下开展大规模、高分辨率的污染研究,可以快速、便捷、有效的提供污染分布信息.

Magnetic properties of the urban soils in Lanzhou and their environmental implications

Magnetic characteristics in 117 surface soil samples collected from Lanzhou City, China were systematically analyzed. Low-coercivity magnetite dominated the magnetic properties in the samples. Values of magnetic mineral concentration parameters were high in the following four areas: (1) the industrial area centered by Lanzhou aluminum plant power and Xigu thermal power plant. (2) Yanerwan, LanDong building materials market enterprise and leather factory. (3) The long and narrow stripe region along the materials market - West Station - Xiaoxihu Park - Chengguan Bridge. (4) The area surrounding Shuishang Park. And low values presented in Anning District (especially Jiuzhou Development Zone) and the south of Qilihe District. In addition, the result from soil profiles showed high values of clf and SIRM in the upper 20cm near the surface and then significantly decreasing, which indicated that contamination was confined in a depth of the upper 20cm. Contrasting with nature samples, magnetic characteristics of polluted materials, such as topsoil, street dust, dust fall, and river sediment, was simplex and dominated by magnetite. Moreover, differences were also observed in the correlation between magnetic susceptibility and percentage frequency magnetic susceptibility, which was positive in nature samples but was negative in anthropogenic materials. Therefore environmental magnetism can be used as a tool for large-scale and high resolution pollution monitoring.