珠江三角洲农业土壤磁化率空间分布特征及其影响因素分析

SPATIAL DISTRIBUTION CHARACTERISTICS OF MAGNETIC SUSCEPTIBILITY OF AGRICULTURAL SOILS AND ANALYSIS OF ITS INFLUENCING FACTORS FOR THE PEARL RIVER DELTA,CHINA

在珠江三角洲范围内选取300件农业土壤样品进行磁化率及频率磁化率分析。结果表明,300件土壤样品的磁化率在1.29×10^(-8)～185.89×10^(-8)m^3/kg范围内变动,平均值为31.20×10^(-8)m^3/kg。珠江三角洲农业土壤磁化率具有明显的空间分异特征,呈南高北低、中心区高东西两翼低的空间分布格局;全区具4个明显的磁化率高值区,分布在:珠海、深圳、惠阳及顺德。因子分析结果表明灌溉方式、土地利用类型和母岩与母质、土壤类型对农业土壤磁化率高低起主要作用。同时,重金属污染对农业土壤的磁性具有明显的增强作用。

Magnetic susceptibility is one of the most basic and easy to be obtained magnetic parameters.A large number of research indicated that it can be used as a proxy for the monitoring of soil heavy metal pollution.Three hundred agricultural soil samples,including 123 samples polluted by heavy metal and 177 samples without heavy metal pollution,were selected from the Pearl River Delta（PRD）,which has become one of the most vigorous economic regions in China,and even in the world since late 1970s.Both low（976Hz）and high（15616Hz）frequency susceptibility（χlf and χhf respectively）were determined using a Kappabridge MFK1-FA triple frequency susceptibility meter（AGICO）.Frequency-dependence magnetic susceptibility（χfd） was calculated from the expression χfd（%）=[（χlf-χhf）/χlf]×100. The results showed that MS of these 300 samples ranged from 1.29×10^-8 to 185.89×10^-8m^3/kg,and the average value was 31.20×10^-8m^3/kg. Overlay analysis for contour map of MS and administrative map of the PRD indicated that significant spatial distributed difference of agricultural soil MS existed within the PRD.MS of agricultural soil was higher at southern area but lower at northern area,and higher within central area but lower within the eastern and western areas. Four regions with obvious high magnetic susceptibility values were distributed at Zhuhai,Shenzhen,Huiyang and Shunde.Considering many factors including natural and anthropogenic activities,factor analysis was performed using statistical software SPSS 13.0.The results indicated that MS of agricultural soil was mainly controlled by irrigation method,land-use type,mother rock type,and soil type.Difference of these factors should be paid much attention during large spatial scale monitoring.Meanwhile,average MS value of heavy metal polluted samples was much higher than that of non-polluted samples,possibly indicating that MS of agricultural soil was enhanced obviously by heavy metal pollution.Though the mechanism of magnetic enhancement for heavy metal polluted agricultural soil retains unclear,soil magnetic susceptibility can indicate heavy metal pollution degree for agricultural soil.