Submersion and exposure from the operation of the Three Gorges Reservoir (TGR) can alter soil properties and plant characteristics at different elevations of the water level fluctuation zone (WLFZ), possibly influencing soil detachment capacity (Dc), but the vertical heterogeneity of this effect is uncertain. Soil samples were taken from 6 segments (5 m elevation per segment) along a slope profile in the WLFZ of the TGR to clarify the vertical heterogeneity of Dc. Scouring experiments were conducted at 5 slope gradients (17.63%, 26.79%, 36.40%, 46.63%, and 57.74%) and 5 flow rates (10, 15, 20, 25, and 30 L min–1) to determine Dc. The results indicate that the soil properties and biomass parameters of the WLFZ are strongly affected by elevation. Dc fluctuates with increasing elevation, with maximum and minimum average values at elevations of 145-150 m and 165-170 m, respectively. Linear equations accurately describe the relationships between Dc and hydrodynamic parameters. τ, ω, and E perform much better than U. Furthermore, a clear improvement is seen when using the general index of flow intensity to estimate Dc. Dc is significantly negatively correlated with MWD (p < 0.05) and organic matter (p < 0.01) but not significantly correlated with other soil properties (p > 0.05). At elevations of 145-150 m and 170-175 m, rill erodibility was greater than at other elevations. The critical hydraulic parameters were highest in the 165-170 m segments, both showing obviously fluctuation in the vertical direction of slope surface. This research highlighted the vertical heterogeneity of the soil detachment and was helpful to understand the mechanisms of soil detachment processes in the WLFZ of the TGR.

Soil aggregates are the basic unit structing soils, and their stability is an important index for soil degradation. However, current methodologies rarely assess the influence of primary soil particles on soil aggregates distribution for different breakdown mechanisms. Therefore, a new method that separates the primary soil particles from the soil aggregates for different breakdown mechanisms with a series of in-lab experiments were developed to fill this gap. The whole soil sample was treated by fast wetting, slow wetting, and mechanical breakdown by pre-wetting and stirring to simulate the different breakdown mechanisms of slaking, differential swelling of clays, and mechanical breakdown by raindrop impact, respectively. Then, attempts were made to separate the primary soil particles from the soil aggregates of various particle size fractions by using sodium hexametaphosphate and hydrogen peroxide to eliminate the influence of the primary soil particles on the soil aggregate distribution. Four soils collected from different areas with different soil textures were used to assess the soil aggregate distribution by using the new method to highlight the importance of separating the primary soil particles from the soil aggregate for different breakdown mechanisms. The results indicated that the primary soil particles have much greater influence on the micro-aggregates than on macro-aggregates. Different breakdown mechanisms and soil types could affect the influence of the primary soil particles affects the on soil aggregate distribution. This study highlights the influence of separate primary soil particles on soil aggregate distribution for different breakdown mechanisms.

Soil aggregates are the basic unit structing soils, and their stability is an important index for soil degradation. However, current methodologies rarely assess the influence of primary soil particles on soil aggregates distribution for different breakdown mechanisms. The purpose of this study was to fill this gap in the literature by developing a new method that separates the primary soil particles from the soil aggregates for different breakdown mechanisms with a series of in-lab experiments. The whole soil sample was treated by fast wetting, slow wetting, and mechanical breakdown by pre-wetting and stirring to simulate the different breakdown mechanisms of slaking, differential swelling of clays, and mechanical breakdown by raindrop impact, respectively. Then, attempts were made to separate the primary soil particles from the soil aggregates of various particle size fractions by using sodium hexametaphosphate and hydrogen peroxide to eliminate the influence of the primary soil particles on the soil aggregate distribution. Four soils collected from different areas with different soil textures were used to assess the soil aggregate distribution by using the new method to highlight the importance of separating the primary soil particles from the soil aggregate for different breakdown mechanisms. The results indicated that the primary soil particles have much greater influence on the micro-aggregates than on macro-aggregates. Different breakdown mechanisms and soil types could affect the influence of the primary soil particles affects the on soil aggregate distribution. This study highlights the influence of separate primary soil particles on soil aggregate distribution for different breakdown mechanisms.