广东小良水土保持观察站花岗岩风化壳磁化率特征及其与生态环境演替的关系

Characteristics of magnetic susceptibility of granite weathering crust and their relationship with succession of ecologic environments in Xiaoliang Soil and Water Conservation Station,Guangdong Province

广东小良水土保持科学研究观测站位于北回归线上,是联合国“人与生物圈”定点观察站。本文在野外考察和系统采样的基础上,分别分析了同一花岗岩风化壳上光板地(生态破坏)剖面和生态恢复剖面样品的矿物学、磁化率特征,探讨它们与生态环境演替的关系。结果表明,在不同生态环境下的两剖面,其磁性矿物类型与粒度均不同,磁化率变化规律差异显著。其中,光板地剖面主要载磁矿物为赤铁矿、针铁矿等矿物,磁化率值很低,与含水量之间相关性较差,基本无超顺磁矿物的存在;生态恢复剖面主要载磁矿物为磁铁矿和磁赤铁矿,低频磁化率值较高且与含水量之间具有良好的相关性,频率磁化率随剖面深度增加而递减,表明超顺磁矿物浓度的变化趋势,反映了生物因素对风化壳剖面的影响和改造。通过两剖面的对比研究说明生态系统的参与对风化壳结构的改变非常显著,磁化率特征可以作为表征这种改变的良好的替代指标。

The Xiaoliang Soil and Water Conservation Station of Guangdong Province is located on the Tropic of Cancer. It is a designated station of Human and Biosphere of the United Nation. Based on the field observation and sampling, this study analyzes the characteristics of mineralogy and magnetic susceptibility of bared-ground （ ecosystem being destroyed） profile and ecosystem-resumed profile, and the implications in the succession of ecologic environments. It is demonstrated that the magnetic susceptibility differs in two granite weathering crust profiles located under different ecosystems, as controlled by different magnetic minerals. Low values of low frequency magnetic susceptibility and its faint correlation with water content are characteristics of the bared-ground profile. The dominant magnetic minerals in the profile are evidenced to be hematite and goethite by power XRD. By contrast, low frequency magnetic susceptibility is much higher in the ecosystem-resumed profile and shows a good correlation with the water content. Magnetite and maghemite is pronounced to be the dominant magnetic minerals by power XRD. The frequency magnetic susceptibility descends with the depth of the profile, which shows a diversification trend of the concentration of superparamagnetic minerals and reflects the effect and alteration of granite weathering crust by biotic factors. There is a definite relation between the characteristics of magnetic susceptibility of the granite weathering crust and the succession of ecologic environments.