Puling Liu

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.

Construction of heilu soil chronofunction in Luochuan, China

Soil chronofunction is an important way to understand soil forming processes quantificationally, and the foundation for establishment of soil genesis model. To establish soil chronofunction, soil properties and 14C ages in the Holocene of heilu soil profile in Luochuan were researched. Linear, logarithmic, and third order polynomial functions were selected to fit the relationships between soil properties and soil ages. The results indicated that, third order polynomial function was the best to fit the relationships between clay (&#60;0.002 mm), silt (0.002–0.02 mm), sand (0.02–2 mm) and soil ages, and the trend line showed the presence of Ah horizon in the profile. The logarithmic function indicated the variation of soil organic carbon and pH with time perferably. The variation of CaCO3 content, Mn/Zr, Fe/Zr, K/Zr, Mg/Zr, Ca/Zr, P/Zr, and Na/Zr with soil age could be described best by use of three order polynomial functions, and the trend line showed migration of CaCO3 and soil elements.

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.

THE SIGNIFICANCE AND RELATIONSHIP OF MAIN CLIMATIC INDICATORS FOR THE HOLOCENE IN NORTHERN SHAANXI

The paleoclimatic indicators certainly contain some climate information,such as temperature,precipitation,monsoon,and so on.However,each indicator expresses the climate information to different degrees.The environmental significance and relationship of climatic indicators need further investigation.In this regard,three Holocene soil profiles in Northern Shaanxi are studied for the change in paleoclimatic indicators.The R/S analysis method was used in this study for the purpose.The results indicate that the magnetic susceptibility of soil(χIf),total content of furrum(TFe),and pH can reflect the change in both temperature and rainfall during the soil formation,whereas the content of calcium carbonate(CaCO3)and the total organic carbon(TOC)are mainly influenced by rainfall and temperature,respectively.The particle size composition(clay fraction0.005mm and coarse silt 0.01~0.05mm)can be used to describe the change of East Asian winter monsoon.This study has provided a theoretical basis and scientific reference for the research on Holocene evolution of paleoclimate.

Quantificational research on the slope development of loess tableland in the Holocene

It is important approach to recognize natural evolution of environment on the Chinese Loess Plateau that researches on evolution of loess landform and soil erosion in the Holocene. In this study, radiocarbon age of soil, loess deposition rate and magnetic susceptibility soil from YCT and YCS profiles which respectively located on loess tableland and an adjacent slope in Yanchang County in northern Shaanxi, were used to reconstruct the landform at about 12000 a B.P. on the slope. The results indicated that the average loess deposition rate of YCT profile in the Holocene was 0.0153 cm/a, and that of YCS profile was 0.0162cm/a during 12295∼20416 a B.P‥ The slope landform had formed before about 12000 a B.P., but its gradient was smaller than the modern slope. So the soil erosion rate greater than the loess deposition rate on the slope, which was the comprehensive result of natural erosion and artificial acceleration erosion. It was proved that this method could be used to quantificational research on loess landform and soil erosion in the geological period, and provided a new idea and method in this study area.