Soil erodibility indicators as affected by water level fluctuations in the Three Gorges Reservoir area, China

The near soil surface characteristics of plant communities probably change considerably with seasonal water-level fluctuations, thus induced corresponding variations in soil erodibility indicators. This study was conducted to investigate the variations in soil erodibility indicators triggered by varying inundation intensity or temporal water-level fluctuations in the Three Gorges Reservoir area. Two non-inundation sites (as the control) and six sites with different water-level fluctuation intensities were selected to measure or calculate eight soil erodibility indicators and then to determine a comprehensive soil erodibility index (CSEI). The erodibility indicators included K factor, slaking rate (SR), mean weighted diameter of aggregates (MWD), mean number of waterdrop impacts (MND), structural stability index (SSI), saturated conductivity (K-s), cohesion (Coh), and penetration resistance (PR). The variation in each soil erodibility indicator could be explained by the changes in near soil surface characteristics of plant community. The results indicated that the MWD, MND, SR, Coh, SSI, and K-s decreased gradually with the intensity of water level fluctuations (IWLFs), while the reverse was found for PR. K factor firstly increased and then decreased with the IWLFs. The CSEI increased with IWLFs, which was closely related to elevation. Compared with the control, CSEI increased by 123.3%, 132.9%, 93.9%, 84.8%, 48.7%, and 55.2% for water levels of 150, 155, 160, 165, 170 and 175 m, respectively. The changes in near soil surface characteristics of the plant community directly led to differences in soil erodibility indicators. Significant positive correlations were detected between soil erodibility indices, and bulk density and sand content, while significant negative correlations were found between root mass density, silt, clay, and organic matter contents. CSEI increased linearly with inundation time and duration. The results are helpful for understanding the mechanism of seasonal fluctuations in soil erodibility for land frequently inundated by water.