Soil aggregate stability response to hydraulic conditions in water level fluctuation zone of the Three Gorges Reservoir, China

Abstract

Soil aggregate stability is a key indicator of soil quality and susceptibility to water erosion. The water level fluctuation zone (WLFZ) of Three Gorges Reservoir (TGR) experiences hydraulic disturbances induced by rainfall, reservoir wave, and water-level fluctuation. Soil aggregate in this region has a unique mechanism of disintegration different from other terrestrial soils. The traditional methods of soil aggregate stability measurement cannot reveal the complex external factors of the soil in the WLFZ. In the present study, an attempt has been made to establish an approach mimicking the real situation in the WLFZ to deeply understand the effects of water movement and periodical wetting on soil aggregate stability in the WLFZ. The soil samples from different elevations were allowed to stay under wetting and wet-shaking conditions for 3 and 81 min, followed by a quantitative separation of disintegrated aggregates by wet-sieving. The mean differences between wetting and wet-shaking for the mean weight diameter (ΔMWD) were highly significant at all elevations for 81 min. Contrary, both treatments applied within a short time period disintegrated aggregates at the same magnitude. Additional to slaking, the kinetic energy applied to soil has induced a mechanical breakdown as a result of water movement. The difference of aggregate stability index (ASI) was highly significant among the elevations p < 0.001 and strongly significant between lower and upper elevations. The Cation Exchange Capacity (CEC) was the most predominant factor determining the stability of soil aggregates with r2 = 0.61, 0.65, 0.69 (p < 0.05) and r2 = 0.71, 0.7, 0.77 (p < 0.05) for ASI, GMD and MWD recorded after wetting and wet-shaking, respectively. Crucially, understanding different effects between arising impacts of water level fluctuations and periodical inundations on soil aggregate stability is a promise for future studies in areas experiencing similar conditions.