| Soil erosion in the Loess Region of China is the most serious all around the world. Such strong brings not only damage to the local ecological environment and sustainable development but also serious safety problems to the downstream of Yellow River.Soil crust is a compact layer formed by rainfall and its runoff effect, and with the features of high intensity, low porosity poor water conductivity, it shows great signifigance in the process of soil erosion.It is more easily develop into soil cruston Loess Plateau because of the climate and soil characteristics there.Sheet erosion is one of the most importanterosion processes on loess hillslope. Coupling effect between soil crust and sheet erosion, especially serious sheet erosion and strong soil crust, will eventually lead to increased rill, ephemeral gully erosion and total erosion.As a reuslt, to study the coupling relationship between soil crustcharacteristics and sheet erosion is extremely important not only to recognize and reveal sheet erosion process and its mechanism, and to further theories of slope erosion., but also to provide an important scientific basis for taking relevant measures on soil and water conservation.With the method of simulated rainfall experiment and soil physical analysis,the coupling relationship of soil crust characteristicswith sheet erosion on loess hillslope were studied under five different rainfall intensities with oneslope and fivedifferent slopes with one rainfall intensities.The study focued onvarious characteristics(bulk density, thickness, hardness and particle composition), the inherent relationships of characteristics soil crusts characteristics,theresponses of soil crusts to sheet erosion of water and sediment and the impact of soil crusts on sheet erosion of water and sediment. The main conclusions were as follows:1 Changing features of soil crust on loess slopeswere studied:(1) Bulk density of soil crust on loess slopes increased with the increase of rainfall intensity while decreased with the increase of slpoe, and their relationship could be describes with a binary logarithmic equation. Slope effected the bulk density more deeply than rainfall intensity. Bulk density of soil crust in different slpoe positon : in the bottom > in the middle > on the top.(2)Thickness of soil crust on loess slopes increased with the increase of rainfall intensity while decreased with the increase of slpoe, and their relationship could be described with a dual power function equation. Slope effected the thickness more deeply than rainfall intensity.In the different intensity of rainfall, thickness of soil crust was greater in the middle of slope while they showed little difference in different positions on one slope.(3)Hardness of soil crust increased with the increase of rainfall intensity while decreased with the increase of slpoe, and their relationship could be described with a Binary logarithmic equation. Slope effected the thickness more deeply than rainfall intensity.Hardness of soil crust in different slpoe positon : on the top> in the middle >in the bottom. Soil water content worked on the hardness. Hardness decreased with the water content increase.(4) The particle composition in soil crust were mainly affected the clay content.2. Internal relationship of soil crust on loess slope was analyzed.(1) Thichness of soil crust increased in different railfall intensities and slopes with the increase of bulk density of soil crust, and their relationship could be respectively decribed with ogarithmic equation, linear equation and linear equation.(2) Hardness of soil crust increased in different railfall intensities and slopes with the increase of bulk density of soil crust, and their relationship could be respectively decribed with ogarithmic equation, ogarithmic equation and linear equation.(3) Hardness of soil crust increased in different railfall intensities and slopes with the increase of thichness of soil crust, and their relationship could be respectively decribed with exponential equation, linear equation and linear equation.(4)There were internal relationships between soil crust bulk density, thickness and hardness. Under the different combination of the rainfall intensity and slopes were positive correlation to the internal relationships. With bulk density of soil crust increasing, thickness of soil crust was thicker, and hardness of soil crust was harder. All of this showed that soil crust can increase soil strength, enhances soil resistance to erosion.3. Soil crust responding to sheet erosionflow and sediment was revealed.(1) Under different rainfall intensity, with average sheet erosion rates of slope increasing, various characteristics of soil crust also increased.Under different slopes, with average sheet erosion rates of slope increasing, various characteristics of soil crust also decreased besides the particles composition D50 of soil crust increasing.The characteristics of soil crust(such as bulk density, thickness, hardness) had higher determination coefficient to average sheet erosion rates. The particles composition D50 of soil crust had lower significant with average sheet erosion rates.(2) Under different rainfall intensity, with average producing flow rates of slope increasing, various characteristics of soil crust also increased. Under different slopes, with average producing flow rates of slope increasing, various characteristics of soil crust also increased.The significant of response between various characteristics of soil crust and average producing flow rates under rainfall intensity was higher than slopes(except the particles composition D50 of soil crust).(3) Under different rainfall intensity, with average water flow power of slope increasing, various characteristics of soil crust also increased. Under different slopes, with average water flow power of slope increasing, various characteristics of soil crust also decreased.The characteristics of soil crust(such as bulk density, thickness, hardness) had higher determination coefficient to average water flow power. The particles composition D50 of soil crust had lower significant with average water flow power.Water depth and raindrop impact is the root cause of various characteristics of soil crust power.4. The effects of to siol crust to Sheet erosion water-sediment characteristics were clarified.(1)The sheet erosion rates, producing flow rates, velocity and water flow power of slope under previous crust soil and no crust soil with the change of rainfall were basically the same.It was first increasing and then stabilized with extended rainfall process. And their relationship could be respectively decribed with ogarithmic equation。The sheet erosion rates of no pre-crust soil was significantly higher than the pre-crust soil. The s producing flow rates, velocity and water flow power of no pre-crust soil were lower than the pre-crust soil.(2)With bulk density and particles composition D50 of pre-crust increasing, the sheet erosion rates decreased. And their relationship could be respectively decribed with power function.(3)With bulk density and particles composition D50 of pre-crust increasing, the producing flow rates increased. And their relationship could be respectively decribed with linear equation and exponential equation.(4)With bulk density and particles composition D50 of pre-crust increasing, the velocity increased. And their relationship could be respectively decribed with linear equation and exponential equation.(5)With bulk density and particles composition D50 of pre-crust increasing, the water flow power increased. And their relationship could be respectively decribed with linear equation and exponential equation. |
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