Effects Of Wind-water Alternate Erosion On Runoff, Sediment And Soil Quality On Loess Plateau, Northwest China

Due to the interactive coupling effects of wind and water erosions in the wind-water erosion crisscrossregion of Loess Plateau, the slope erosion in the region was quite serious, and the erosion process was quitecomplicated. By using wind tunnel combined with simulated rainfall, this paper studied the change of sloperunoff and sediment yield, soil particle, soil water-holding capacity and soil nutrient under wind-wateralternate erosion, and quantitatively analyzed the effects of wind erosion on water erosion and therelationships between wind and water erosions. The study will be helpful to deeply understand the soilerosion mechanisms, and provided theoretical foundation for evaluating the environmental effect ofwind-water alternate erosion.1. Wind erosion influences the quantitative relation between infiltration and runoff and rainfallintensity by changing the micro-topography and soil physical properties. The change tendency ofinfiltration and runoff process and hydrodynamic parameter variation were different under different windspeeds and rainfall intensities. Compared with the rainfall intensity, wind speed had more significantinfluence on slope runoff producing time. There was a critical value at the range of60～80mm·h^-1, whichhad a significant influence on rainfall and infiltration process. At the rainfall intensity of60,80, and100mm·h^-1, compared with no wind erosion, wind erosion treatment could reduce rainfall infiltration rate by2.9～10.0%, increase slope runoff intensity by4.5～21.7%. At the rainfall intensity of120mm·h^-1, thechange process of infiltration and runoff was contrary to that of60,80, and100mm·h^-1. At the rainfallintensity of150mm·h^-1and runoff time more than15min, the change process was similar to that of60,80,and120mm·h^-1. Hydrodynamic parameter was closely related to wind speed and rainfall intensity. Theflow speed, flow depth, flow shear stress, unit stream power exhibit a positive correlation with wind speedand rainfall intensity, whereas drag coefficient exhibit a negative correlation with wind speed and rainfallintensity. At the rainfall intensity of120and150mm·h^-1, the slope infiltration and runoff had a greatinfluence on hydrodynamic parameter.2. Wind erosion promoted the development of micro-topography, and altered the quantitativerelationship between the sediment yield under water erosion and the variation of rainfall intensity. Therewas an obvious positive interaction between wind and water erosions. At the rainfall intensity of60and80mm·h^-1, the sediment yield without wind erosion decreased with the duration of rainfall and tended to bestable, but the sediment yield with wind erosion decreased to a certain valley value first, and then showed an increasing trend. At the rainfall intensity of60,80, and100mm·h^-1, the sediment yield with the winderosion at speeds of11and14m·s-1increased by7.3～27.9%and23.2～39.0%respectively, as comparedwith the sediment yield without wind erosion. At the rainfall intensity of120and150mm·h^-1and in therainfall duration of15minutes, the sediment yield with and without wind erosion presented a decreasingtrend, but, with the increase of rainfall duration, the sediment yield with wind erosion showed a trend ofdecreasing first and increasing then, as compared with the sediment yield without wind erosion. Wind andwater erosion mutually increased the surface roughness of soil. The bigger the intensity of wind speed andrainfall intensity, the more obvious the alteration of slope shape.3. Wind erosion influenced the quantitative relation between sediment particles and rainfall intensityby changing the physical properties of the eroded soil. Compared with no wind erosion, water-windalternate erosion resulted the fine particle in sediment increased by2.7～18.9%, medium particle increasedby1.2～3.6%, and coarse particle decreased by3.7～9.3%. However, the enrichment regularity ofsediment particles was not the same in different rainfall intensities and different rainfall durations.Compared with no wind erosion, the sediment particles with the wind erosion had a significant change atspeed of11and14m·s-1under the rainfall intensities of60,80, and100mm·h^-1. Under the rainfall intensityof150mm·h^-1and runoff time more than15min, the sediment particle had less change.4. Under the condition of water erosion, compared with no wind erosion, the nutrient of topsoil （0～1cm） and sediment with wind erosion decreased. Soil water-holding capacity was decreased under watererosion, the wind factor had more influenced on soil water than water factor. Wind erosion was sufficientlystrong to modify the texture of the topsoil and lift the fine particles and move the larger particles, soil fineparticle （<0.01mm） decreased9.8～10.8%, and coarse particle （>0.05mm） increased16.8～20.8%atspeeds of11and14m·s-1. Soil organic and nitrogen were associated with the fine particles and loss in theprocess wind erosion. In the crisscross region of wind and water erosions, water erosion interrupted the soilcapillary porosity and decreased the soil water-holding capacity. At rainfall intensities of60,100, and150mm·h^-1, compared with no wind erosion, soil water （0～6cm） with wind erosion decreased obviously atspeed of6m·s-1. Wind factor had more significant influence on soil water than rainfall factor.