杭州城区土壤的磁性与磁性矿物学及其环境意义

对杭州城区四个不同功能区块土壤进行了系统的环境磁学测定，结果表明城市土壤的磁化率平均值为128×10^-8m³·kg^-1，频率磁化率平均值3.6%(样品数=182)，城市土壤呈现明显的磁性增强. 城市土壤的磁化率与频率磁化率呈极显著指数负相关，表明城市土壤磁性增强明显区别于自然成土过程引起的以超顺磁性(SP)颗粒为主的表土磁性增强机理. 统计分析表明,城市土壤磁化率与软剩磁和饱和等温剩磁(SIRM)呈显著直线正相关，说明亚铁磁性矿物是城市土壤剩余磁性的主要载体. 综合等温剩磁获得曲线、热磁曲线、磁滞回线等岩石磁学测定和SEM/EDX分析，城市土壤的磁性矿物以磁铁矿和赤铁矿为主，磁性矿物以假单畴-多畴（PSD-MD）颗粒存在，粒度明显大于成土过程形成的磁性颗粒，这些磁性颗粒主要来自燃料燃烧、汽车尾气等环境污染物. 因此，城市土壤磁测可作为城市土壤污染监测、污染空间分布和污染物来源判断的新手段.

Magnetic characterization and magnetic mineralogy of the Hangzhou urban soils and its environmental implications

A detailed magnetic study of urban soils in Hangzhou City, China, was carried out using combined environmental magnetism and rock magnetism techniques. Magnetic measurements showed that those urban soils have a significant magnetic enhancement, which were characterized by higher magnetic susceptibility (average 128×10^-8m³·kg^-1) and magnetic remanence, and low frequency-dependent susceptibility (average 3.6%, N=182). Magnetic susceptibility values of urban soils showed highly significant negative correlation with frequency-dependent susceptibility, indicating that the mechanism of the magnetic enhancement of urban soils is different from contribution of pedogenic ferromagnetic minerals in nature soils. Magnetic susceptibility values of urban soils, on the other hand, have significantly positive correlation with Soft IRM (IRM_20mT) and saturation isotherm remanent magnetization (SIRM), suggesting that ferrimagnetic minerals are the main magnetic carriers. The combined rock magnetism (acquisition curves of IRM, temperature-dependent susceptibility and hysteresis measurement) and SEM/EDX (scanning electron microscopy and energy dispersive X-ray analysis) revealed that magnetic mineralogy of urban soils is dominated by magnetite-like and hematite-like phases. The hysteresis parameters suggested that they are present mainly in the pseudo-single domain (PSD) and multidomain (MD) grains, which is attributed to input of anthropogenic magnetic grains from industrial activity, fuel combustion and traffic pollution. This finding suggested that magnetic measurements could be used as potential tools for monitoring soil pollution, mapping spatial distribution of pollution, and differentiating sources of pollutants in urban soils.