Abstract:

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.

Key words: Three-gorge Reservoir region, riparian zone soil, water level, magnetic characteristic, magnetite