Study On Coupling Relationship Between Vegetation And Soil Erosion In A Semi-arid Loess Hilly Region

The Loess Plateau is one of the areas with the most severe water and soil erosion in the world today,especially the issue of water erosion,and it has become one of the largest environmental problems in the Yellow River Basin and even in China.The party and the country have always attached great importance to the construction of the ecological environment on the Loess Plateau.With the implementation of the conversion of farmland to forests(grass)and closure policies and the enhancement of soil and water conservation work,the vegetation coverage in the Loess Plateau has been significantly improved.Changes in vegetation cover directly affect the process and intensity of water cycle in the river basin,and have an impact on regional production,sand production,sediment transport,and other processes.Therefor the regulation of vegetation on soil erosion and water-sediment relationship and its critical rainfall dynamics were analyzed to provide theoretical support for scientific assessment of the effects of valence on water and sediment regulation and understanding of the causes of water and sediment changes in the Yellow River.In this paper,a field outside diameter flow test plot was constructed in the Luoyugou water and soil conservation science experimental station in the third sub-area of the Loess Hilly-gully region.In the artificial rainfall simulation experiment in the different coverage grassland was studied,soil moisture,rainfall infiltration,runoff,sediment yield process nonlinear response of vegetation.The laws of soil moisture,infiltration,runoff,and sediment yield under vegetation effects were clarified,and the regulation effect of vegetation on soil erosion and sediment transport,and the critical rainfall dynamics were revealed.The results show:(1)For natural condition,the vertical change in soil moisture could be divided into four levels: the rapid change layer(0-20cm),the active layer(20-30cm),the second active layer(30-40cm),and the relatively stable layer(deeper 40cm).There was stratification in the vertical distribution of soil moisture,and the slope distribution of soil moisture had significant differences in slope position(P < 0.05).Frequent exchange of soil moisture and air was also concentrated in the 0-40 cm soil layer range.During the rainfall,the activity of soil moisture was obviously enhanced,but the influence was mainly in the range of 0-30 cm soil layer,the influence of soil moisture by rainfall was negatively correlated with the soil depth.The change of soil moisture of 0-30 cm soil layer with time was not uniform,there were 3 periods of the rapid rise period,the stable period and the slight decline period.In deeper soil layer,there was a gradient difference in the vertical variation of soil moisture.Except for the surface soil,the rainfall infiltration only increases the soil moisture of each soil layer,while the proportion of soil moisture did not change,the distribution of soil moisture in the slope was more significant(P < 0.01)(2).With the increase of soil moisture of 0-30 cm soil layer,the runoff rate showed the trend of increase to a stable value.The sediment yield rate increased to a peak value,and then decreased,became stable gradually.(3)with the increase of grass cover and rainfall intensity,soil infiltration rate was increasing,the soil infiltration rate increased significantly with the increase of grass coverage rate.The initial infiltration rate of soil and rainfall intensity presented exponential relationship.The soil stability infiltration rate and rainfall intensity showed the power function relations.(2)The cumulative soil infiltration and rainfall time of had a good power function relationship.The cumulative infiltration of soil increased significantly with the increase of grass coverage rate.The effect of rainfall intensity on soil cumulative infiltration was a gradient difference.(3)The increase of grass cover could significantly increase the soil infiltration coefficient,the soil infiltration coefficient decreased with the increase of rain intensity,under the coverage of field grass(about 60%),Below 1.5mm / min,the role of grass in increasing soil infiltration coefficient was obvious.(4)The relationship between soil infiltration rate and rainfall time was fitted by four infiltration models,it was found that the Horton formula could simulate the soil infiltration process well.(5)The runoff time is prolonged with the increase of grass cover,and it is shortened with the increase of rainfall intensity.And the rainfall intensity has a goodpower function relationship with the runoff time.The runoff gradually decreases with the increase of vegetation coverage.The greater the grass cover,the more obvious the decreasing trend.The runoff increases gradually with the increase of rainfall intensity.The greater the rainfall intensity,the more obvious the increasing trend.Grass is covered to retain silt and has good filtration effect.Under different rainfall intensities,there is a phenomenon that large rainfall intensity produces a small rate of sand production on the slope sediment yield rate.Comparing the effects of grass coverage and rainfall intensity on the rate of sediment production,indicating that grass coverage is significantly greater than rainfall intensity.However,as the rainfall duration continues,runoff erosion erosion caused by rainfall intensity gradually plays a leading role.