| The Loess Plateau is the main soil erosion area in China and the most serious area of soil erosion in the world.In recent years,the state and local governments have implemented a number of vegetation restoration projects,which have certain positive effects on improving soil corrosion resistance.The current research content mainly focuses on two aspects: First,many experiments only use the indicator of erosion to reflect the change law of soil erosion.Second,the amount of agglomerate fragmentation and migration changes during the sputtering process.However,the essential problem of the relationship between the amount of suspension and transport of soil aggregates by thin-layer runoff during rainfall is rarely studied,and the research on the particle size distribution characteristics of erosion aggregates is relatively rare.In this experiment,a variable needle raindrop simulation device and a self-made runoff simulation device were used to test the water erosion of raindrop splashing and runoff erosion on loess soil and sandy loam soil in the Loess Plateau.The raindrop diameters are 0 mm,2.67 mm,3.05 mm,3.39 mm,3.79 mm,and 4.05 mm,respectively.The runoff depths are 0 mm,1 mm,3 mm,and 5 mm,respectively.The mud produced during the test was collected in a plastic bucket,and the amount of erosion,sediment concentration and runoff were calculated by weighing.The slurry is then subjected to wet sieving treatment to obtain agglomerates of different particle sizes,and the particle size is divided as follows: >2 mm,1-2 mm,0.5-1 mm,0.25-0.5 mm,0.106-0.25 mm,0.053-0.106 mm,and <0.053 mm.,a total of 7 levels.The agglomerates were dried to constant weight and the results were weighed.In order to reveal the characteristics of thin-layer runoff on the suspension and migration of soil aggregates under the impact of raindrops.By analyzing the experimental data,the following results were obtained:(1)Sediment distribution and transport characteristics.Under the same shallow flow deep erosion,the sediment erosion of sandy loam and loess soil increased with the increase of raindrop diameter.Under the same raindrop diameter splash,when the raindrop diameter is ≤ 2.67 mm,the amount of erosion increases with the increase of the shallow flow depth.Under the raindrop diameter>2.67 mm,with the increase of runoff depth,the amount of soil erosion increased first and then decreased.Under the influence of raindrop splashing,the sediment concentration of sandy loam and loess soil generally showed a decreasing trend with the increase of runoff depth.Under the same diameter raindrops,the runoff of sandy loam and loess soil gradually increases with the increase of shallow flow depth.(2)Distribution and migration of agglomerates.Under the erosion,the particle size distribution of sandy loam soil: when the raindrop diameter is ≤ 3.39 mm,the particle size of the aggregate agglomerate is <0.053mm;when the diameter of the raindrop is > 3.39 mm,the particle size of the aggregate aggravation is 0.25-0.106 mm.The agglomerates with the largest amount of erosion of the loessial soil under different diameter raindrops are particle size <0.053 mm,and gradually decrease with the increase of the diameter of the raindrops.Under the eclipse,the particle size of the two soil transport and migration aggregates mainly concentrated <0.053 mm.Under the combination of raindrop impact and runoff erosion,the erosion particle size distribution of the sandy loam soil under the raindrop diameter ≤ 3.39 mm showed a bimodal curve distribution,the highest peak value was <0.053 mm,and gradually decreased with the increase of runoff depth;The peak value is a particle size of 0.25-0.106 mm and gradually increases as the depth of the runoff increases.When the raindrop diameter is >3.39 mm,the particle size distribution of the sandy loam soil becomes a unimodal distribution,mainly due to the increase of the erosion amount of 0.25-0.106 mm.The particle size distribution of agglomerates of loessial soil showed a single-peak curve under mixed erosion,and the peak value was <0.053 mm,and gradually decreased with the increase of shallow flow depth.(3)Change law of characteristic parameters of agglomerates.There is a quadratic function relationship between the MWD value of the sandy loam and the loess soil aggregate and the raindrop diameter d.There is a quadratic function relationship between the MWD values of the two soil aggregates and the shallow flow depth h.When the diameter of raindrops is small,the D value of sand loam soil increases first and then decreases with the increase of shallow flow depth.When the diameter of raindrops is larger,the D value decreases with the increase of shallow flow depth.The D value of loessial soil under each raindrop diameter showed a decreasing trend with the increase of shallow flow depth.It provides certain guiding significance for improving soil and water conservation measures on the Loess Plateau. |
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