Effects of seasonal water-level fluctuation on soil pore structure in the Three Gorges Reservoir, China
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Inundation of the Three Gorges Reservoir has created a 30-m water-level fluctuation zone with seasonal hydrological alternations of submergence and exposure, which may greatly affect soil properties and bank stability. The aim of this study was to investigate the response of soil pore structure to seasonal water-level fluctuation in the reservoir, and particularly, the hydrological change of wetting and drying cycles. Soil pore structure was visualized with industrial X-ray computed tomography and digital image analysis techniques. The results showed that soil total porosity (> 100 μm), total pore number, total throat number, and mean throat surface area increased significantly under wetting and drying cycles. Soil porosity, pore number and throat number within each size class increased in the course of wetting and drying cycles. The coordination number, degree of anisotropy and fractal dimension were indicating an increase. In contrast, the mean shape factor, pore-throat ratio, and Euler-Poincaré number decreased due to wetting and drying cycles. These illustrated that the wetting and drying cycles made soil pore structure become more porous, continuous, heterogeneous and complex. It can thus be deduced that the water-level fluctuation would modify soil porosity, pore size distribution, and pore morphology in the Three Gorges Reservoir, which may have profound implications for soil processes, soil functions, and bank stability.
KeywordsSoil pore structure X-ray computed tomography Image analysis Wetting and drying cycles Water-level fluctuation Three Gorges Reservoir
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This work was funded by the National Natural Science Foundation of China (Grant No. 41771321, 41771320 and 41571278) and Sichuan Science and Technology Program (Grant No. 2018SZ0132). We appreciate Professor Xinhua Peng and Associate Professor Hu Zhou of the Institute of Soil Science, Chinese Academy of Science for guiding on the image analysis.
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