Jiaqiong Zhang

Response of soil detachment rate to the hydraulic parameters of concentrated flow on steep loessial slopes on the Loess Plateau of China

Using hydraulic parameters is essential for describing soil detachment and developing physically based erosion prediction models. Many hydraulic parameters have been used, but the one that performs the best for describing soil detachment on steep slopes when the lateral expansion (widening) of rills is not limited has not been identified. An indoor concentrated flow scouring experiment was performed on steep loessial slopes to investigate soil detachment rates for different flow rates and slope gradients. The experiments were conducted on a slope-adjustable plot (5 m length, 1 m width, 0.5 m depth). Sixteen combinations of four flow rates (10, 15, 20 and 25 L min–1) and four slope gradients (17.6%, 26.8%, 36.4% and 46.6%) were investigated. The individual and combined effects of slope gradient and flow hydraulic parameters on soil detachment rate were analyzed. The results indicated that soil detachment rate increased with flow rate and slope gradient. Soil detachment rate varied linearly and exponentially with flow rate and slope gradient, respectively. Multivariate, non-linear regression analysis indicated that flow depth exerted the greatest influence on the soil detachment rate, followed by unit discharge per unit width, slope gradient, and flow rate in this study. Shear stress and stream power could efficiently describe the soil detachment rate using a power equation. However, the unit stream power and unit energy of the water-carrying section changed linearly with soil detachment rate. Stream power was an optimal hydraulic parameter for describing soil detachment. These findings improve our understanding of concentrated flow erosion on steep loessial slopes.

Effects of slaking and mechanical breakdown on disaggregation and splash erosion

&NA; The contributions of different mechanisms of aggregate breakdown to splash erosion are still obscure. This study was designed to investigate the effects of various mechanisms of soil disaggregation on splash erosion. Loamy clay, clay loam and sandy loam soil types were used in this research. Soil aggregate stability was determined by the Le Bissonnais method. Deionized water was used to simulate the combined effect of slaking and mechanical disaggregation, whereas alcohol was used to estimate the contribution of mechanical breakdown only. Simulated rain with an intensity of 60 mm hour−1 was applied at five heights (0.5, 1, 1.5, 2 and 2.5 m) to achieve different amounts of rainfall kinetic energy. The results indicated that the rate of splash erosion increased with the increase in rainfall kinetic energy in tests with both deionized water and alcohol. The rates of splash erosion for three types of soil followed the order of loamy clay soil < clay loam soil < sandy loam soil, but the mean weight diameter (MWD) of disintegrated aggregates followed the reverse order. The rates of splash erosion from the effects of slaking and mechanical breakdown increased with an increase in rainfall kinetic energy. The contributions of slaking and mechanical breakdown to splash erosion decreased for the former, whereas it increased for the latter as rainfall kinetic energy increased. The slaking effect contributed more than 50% of splash erosion. The rates of contribution of slaking and mechanical breakdown to splash erosion depended on rainfall kinetic energy and soil type. HighlightsContributions of different mechanisms of aggregate breakdown to splash erosion remain obscure.Alcohol was used to simulate the effect of mechanical breakdown only.Slaking contributed more than 50% of splash erosion.Contributions by mechanisms of aggregate breakdown depend on rainfall kinetic energy and soil type.

Sediment transport capacity of concentrated flows on steep loessial slope with erodible beds

Previous research on sediment transport capacity has been inadequate and incomplete in describing the detachment and transport process of concentrated flows on slope farmlands during rill development. An indoor concentrated flow scouring experiment was carried out on steep loessial soil slope with erodible bed to investigate the sediment transport capacity under different flow rates and slope gradients. The results indicated that the sediment transport capacity increases with increasing flow rate and slope gradient, and these relationships can be described by power functions and exponential functions, respectively. Multivariate, nonlinear regression analysis showed that sediment transport capacity was more sensitive to slope gradient than to flow rate, and it was more sensitive to unit discharge per unit width than to slope gradient for sediment transport capacity in this study. When similar soil was used, the results were similar to those of previous research conducted under both erodible and non-erodible bed conditions. However, the equation derived from previous research under non-erodible bed conditions with for river bed sand tends to overestimate sediment transport capacity in our experiment.

Impacts of biochar application rates and particle sizes on runoff and soil loss in small cultivated loess plots under simulated rainfall

Increasing literature suggests that biochar can be used to improve soil fertility and subsequently benefit crop yield. However, the effects of biochar application rates and particle sizes on soil erosion processes have yet to be fully identified. The objective of the present study was to evaluate the influence of biochar with different application rates and particle sizes on soil erosion. Addition of biochar to loess generally increased the mean time to runoff by 19.47% relative to the control. The time to runoff decreased with an increase in the biochar application rates and fluctuated with a decrease in biochar particle sizes. The combined 1% and <0.25 mm biochar treatment yielded the longest time to runoff (2.97 min) and the lowest runoff (36.23 kg m-2 h-1) and soil loss (1.33 kg m-2 min-1). Biochar addition decreased the total runoff volume by 12.21% and generally inhibited soil loss under lower application rates (1% and 3%) while promoting soil loss under higher application rates (5% and 7%). With a decrease in biochar particle size, total runoff volume increased under the 5% and 7% biochar, but no uniform trend was observed under the 1% and 3% biochar treatments. The total soil loss increased with increasing biochar application rates, whereas a negative trend was observed with decreasing biochar particle sizes. The contribution of biochar application rates to runoff and soil loss rates was distinctly greater than the biochar particle sizes. Additionally, biochar addition could increase >2 mm water-stable soil aggregates and saturated hydraulic conductivity (Ksat) in this study. We inferred that the positive effects on soil and water loss were potentially due to the improvement in >2 mm water-stable soil aggregates and Ksat. The results implied that soil-biochar additions could be a potential measure for conserving soil and water in the Loess Plateau.