The Effects of Timing of Inundation on Soil Physical Quality in the Water-Level Fluctuation Zone of the Three Gorges Reservoir Region, China

Abstract

With the completion of the Three Gorges Dam, soils between the elevations of 145 and 175 m are exposed or submerged seasonally. Soil hydrological and physical properties are changed. A detailed investigation was performed to examine the influence of the timing of inundation on soil physical quality. Samples were collected in the water level fluctuation (WLF) zone and non-WLF zone in Zhongxian County, Chongqing. Soil samples were taken from depths of 0 to 10, 10 to 20, 20 to 30, and 30 to 40 cm. Soil structural quality was assessed by the visual evaluation of soil structure (VESS) method in situ; mean weight diameter (MWD and mass fractal dimension () were measured to represent soil aggregate stability; and the soil water retention curve and computed microtomography (micro-CT) images were used to show soil pore networks. Our findings show a deterioration of soil structure indicated by a high structural quality (Sq) score in VESS (the higher the Sq score, the worse the soil structural quality) and a decline in soil aggregate stability indicated by low MWD and low in the WLF zone. The data from both the soil water retention curve and micro-CT images demonstrate a deterioration of soil physical quality through decreased porosity and a shift of drainable micropores (0.1 < radii < 125 μm) to non-drainable micropores (radii < 0.1 μm) in the WLF zone of the Three Gorges Reservoir. The potential of environmental hazards of soil in WLF zone was also investigated.