The effects of the reverse seasonal flooding on soil texture within the hydro-fluctuation belt in the Three Gorges reservoir, China

The formation of the large hydro-fluctuation belt at the altitude of 145-175 m, following the construction of the Three Gorges Dam, developed from the terrestrial system in the Three Gorges reservoir. This research mainly concerned the effects of the resultant reverse seasonal flooding on soil texture. Four field experimental plots were designed with sample belts and quadrats at the head, middle, and tail sections of the reservoir area. Stratified soil samples were collected, followed by analysis of soil structure and soil grain size of the collected samples. The reverse seasonal flooding significantly changes texture and nutrient of riparian soil. The percentages of silt and clay formations were greatest at the lower hydro-fluctuation belt, followed by the middle and upper hydro-fluctuation belt, respectively. The percentage of silt and clay particles at 150 m was greater than that of 170 m by 18.12%. Conversely, the percentage of sand particles at the upper hydro-fluctuation belt ranked the highest, and followed by the middle and lower hydro-fluctuation belt, respectively. The percentage of sand particles at 170 m was higher than that at 150 m by 19.72%. Soil texture type changed with increasing altitude gradient, from silt loam, loam, then to sandy loam. Reverse seasonal flooding also promotes silt and clay permeation, and deposition from surface soil to subsurface soil, increasing homogeneity in grain structure between soil layers. This change in soil texture is associated with changes in soil nutrients. The content of soil organic matter, total nitrogen, total phosphorus, and total potassium varied significantly among soil texture types, with loam having the highest soil nutrient concentration and sandy loam having the lowest. The reverse seasonal flooding promotes the deposition of clay and silt within the hydro-fluctuation belt, inducing the total texture change of loam to silt loam. However, the structures and attributes of soil texture varied along the altitude gradient, as the exposed and submersed season and time span of riparian soil changed with the increase of altitude.