Magnetic properties of urban soils from typical oasis cities and their environmental implications

This study is a systematic analysis on the environmental magnetic properties, soil texture and distribution of heavy metals content in topsoil sampled from typical oasis cities in desert like Wuhai, Shizuishan and Yinchuan. The results indicated that the topsoil in Wuhai and Shizuishan is typical sandy soil, while that in Yinchuan is sandy loam. Magnetic properties of topsoil samples are all predominated by ferrimagnetic magnetic mineral (magnetite) of coarse pseudo single domain (PSD)-multi domain (MD) particles with magnetic susceptibility of 152 X 10(-8), 104X10(-8), and 117x10(-8)m(3).kg(-1) respectively for the three cities. The magnetic mineral content and magnetic particles size in topsoil samples of Wuhai are significantly higher than that of Shizuishan and Yinchuan. Pollution Load Index (PLI) of heavy metals (Cr, Cu, Pb, Zn, Fe) showed that there is slight pollution in the three cities. Dotted distribution of high values of magnetic susceptibility and Pollution Load Index is shown in nonindustrial area, whilst planar distribution with high value is shown in industrial area. The correlation coefficient between magnetic parameters and heavy metals of topsoil in Wuhai is significantly higher than that in Shizuishan and Yinchuan, which suggests that magnetic parameters are more advantageous for evaluation on pollution degree in regions with single pollution source. There is an increase by the same degree in magnetic susceptibility in parallel with the increase of Pollution Load Index, despite of the significant difference of magnetic properties among three cities. Therefore, magnetic susceptibility can be used as the unified and effective substitute indicator to evaluate the pollution degree of heavy metals in topsoil of Ningxia plain.