三峡库区消落带土壤磁性变化规律及成因探讨

为动态跟踪三峡库区消落带土壤物性在水位上涨后所受影响，选择重庆市忠县石宝寨镇长江左岸一带作为研究区，以消落带外同类型土壤作对照，从分析不同水位土壤的磁学性质入手，探究三峡库区蓄水前后土壤性质对环境变化的响应。库区蓄水后，不仅导致了消落带内土壤理化性质变化，还使土壤磁性空间分布在不同水位这一维度上发生显著改变。消落带监测断面数据显示，土壤磁性由蓄水前垂直方向上较稳定的分布，变为目前整体上随淹没水深增加而增高的特征；169~175 m高程附近，土壤磁性接近当地同类土壤背景值，而低于此高度尤其是低于157 m后，磁化率值迅速增高。磁性的变化是库区蓄水后土壤磁性矿物组成发生改变造成的，由热磁曲线可知，次生磁铁矿的加入是首要原因。扫描电镜下观测出的浑圆状磁铁矿的最可能来源是上游燃烧化石燃料排放的磁性外来污染物，其随江水输运至此并沉积吸附在土壤颗粒上。研究结果为间接监测污染物的迁移提供了依据。

Discussion of Characteristics and Origin of Soil Magnetism Changes in the Three-gorge Reservoir Riparian Zone

In order to dynamically track the property change of soils in the riparian zone of the Three-gorge Reservoir, taking the left bank of Yangtze River at Shibaozhai Town, Zhong County, Chongqing as an example, the magnetic properties of soils in the riparian zone at different water levels were studied and compared with same-type soils outside the riparian zone, furthermore the responses of physical property of soils before and after water storage to the environment change were analyzed. Based on the analysis of all major monitoring-section data in the riparian zone, the results reveal that after water storage not only the physical and chemical properties of soils in the riparian zone changed, but also the magnetic spatial distribution in different water level was significantly distinct; before water storage the vertical distribution of magnetic susceptibility of soils in the riparian zone was relatively stable, but after water storage the magnetic susceptibility of soils increased with submerged-depth increasing; in depth of 169-175 m, the magnetic susceptibility of soils was same to the background value, but it increased rapidly below this depth range, especially below 157 m.This change is resulted from the difference of magnetic mineral composition of soils caused by water storage; learned by thermal magnetic curves (χ-T curves), the most important reason is that the magnetite has been mixed. The distant pollutant is an important potential source of rounded magnetite discovered under the SEM, such as mining and other heavy polluting enterprises burning of coal, oil and other fossil fuels at the upper river. The distant pollutant is transported to this area along Yangtze River and is adsorbed or deposited to soil particles after water storage. This study can provide a basis for indirect monitoring contaminant migration in this area in the future.