| Soil wind erosion and dust pollution in typical northern part of north china are one of the important sources leading to soil erosion and atmospheric environmental quality problems in this area.however,the effect and mechanism of soil wind erosion and soil dust emission reduction are not clear.Taking Zhangbei area of Zhangjiakou and Yanqing area of Beijing as the research area,selecting different vegetation measures and different conservation tillage measures land as the research object,through field monitoring and indoor wind tunnel simulation,this paper explores the effectiveness and mechanism of vegetation restoration and conservation tillage measures to prevent soil wind erosion and dust pollution,and tries to provide reference and basis for the allocation of wind erosion and dust control measures in this area.The main findings are as follows:(1)The characteristics of wind and sand flow structure were carried out by using indoor wind tunnel.In the single vegetation measure,the sand transmission rate was large stilettos from large to small,and the measures of evergreen conifers and broad leaves,grass and shrubs,and in the combination of vegetation measures,the sand transmission rate was the largest under the combination measures of Joe irrigation,and the smallest under the combination measures of Joe grass.In the vertical direction,under the single vegetation measure,the sand transmission rate conforms to the exponential function relationship with height,and under the combined vegetation measure,the sand transmission curve is"C"shape,showing a unique"like nose effect".With the increase of wind speed,the soil erosion rate under different conservation farming measures increased gradually,while the soil wind erosion rate increased with the increase of wind speed under the combination measures of retaining mulch,the soil erosion rate of chestnut soil was greater than the brown soil,the soil erosion rate and the density,height and herb cover were all negatively related,and the soil erosion rate under the mixed pattern was significantly greater than the block-mix editing method.(2)By conducting a study on the influence factors of soil dust emissions,we found that soil dust emissions increased exponentially with increased wind speed when vegetation measures were taken,and R~2 was greater than 0.93.The emission of chestnut calcium dust at the same wind speed is greater than that of brown soil.With the increase of the vegetation density and height and herb cover,the soil dust emission showed a decreasing trend to varying degrees,after taking the combined vegetation measures,compared with the single vegetation measures,the soil fine particle stakes were increased to varying degrees,and the dust emissions under the retention measures were greater than the residual cover measures,and with the increase of the density and height of the retention,the dust emissions showed a downward trend.(3)Through spectral analysis of soil wind erosion and dust particles,we found that when vegetation measures were taken,the particle size of soil wind erosion showed a monomodal distribution.The particle size of soil wind erosion was mainly≤250μm;the particle size of soil dust particles was≤10μm.the Lord.Among the four single vegetation measures,the deciduous broad-leaved measure has the best effect on reducing the emissions of particles with a particle size of≤250μm in the soil wind erosion;the evergreen needle-leaved measures and the deciduous broad-leaved measure have the best effect on the particle size of the soil dust in the range of 10-100μm.The emission reduction effect of particulate matter is relatively good.Among the combined vegetation measures,the combined vegetation measures based on deciduous broad-leaved vegetation have the best effect on reducing the particulate matter of soil wind erosion with a particle size of≤250μm;the combined vegetation measures based on deciduous broad-leaved vegetation have the best effect on the medium particle size of soil dust The emission reduction effect of fine particulate matter in the range of 10-100μm is relatively good.Protective farming measures are better than those with a particle size≤250μm in reducing soil wind erosion.The particle size of soil dust under protective tillage measures is mainly≤10μm,and the reduction effect of protective tillage measures on the particle size of soil dust≤10μm is better than that of particle size between 10-100μm.The combined measures of stubble cover have the best emission reduction effect on the fine particulate matter with a particle size≤250μm in the soil wind erosion;the combined measures of stubble cover have the best emission reduction effect on the fine particulate matter with a particle size≤10μm in the soil wind erosion.(4)The horizontal diffusion distance of dust particles driven by soil wind erosion:the diffusion distance of particles with particle size around 100μm is generally below 15m.For particles with particle size of 10μm,the diffusion distance is generally 30km～150km.Particulate matter with particle size around 2.5μm diffuses over thousands of km.As for the vertical diffusion distance of dust particles driven by soil wind erosion,in the range of 10m from the earth’s surface,in general,with the increase of height,the mean particle size decreases exponentially.The mean particle size is less than 15μm in the height of 5m and around 10μm in the height of 10m.(5)Under the various vegetation measures and various conservation farming measures,with the increase of wind speed,the contribution of soil wind erosion to TSP,PM10 and PM2.5 emissions decreased slowly and then decreased sharply,and with the increase of wind speed,the contribution of soil wind erosion to the larger particles in soil dust decreased even more.The relative content of fine particles in soil erosion of brown soil is greater than that of chestnut calcium soil.In each vegetation measure,when the measures of deciduous broad-leaved vegetation and the combined vegetation measures based on deciduous broad-leaved vegetation were taken,the emission reduction effect of fine particles such as dust was relatively optimal.(6)When optimizing the configuration of vegetation structure for the purpose of reducing soil erosion in northern China:poplar density remained above 945 plants/ha,pine tree density was maintained at 1388 plants/ha,and lime density was maintained at more than 1108 plants/ha.When optimizing the configuration of vegetation structure for the purpose of reducing soil dust discharge driven by soil erosion:poplar density remained above 1494 plants/ha,pine tree density was maintained at 1348 plants/ha,and lime density was maintained at 1423 plants/ha or more.When optimizing the configuration of the retention structure for the purpose of reducing soil erosion in northern China:the retention height is maintained at more than 63.29cm.In order to reduce soil dust discharge driven by soil erosion,when the retention structure is optimized for configuration:the retention height is maintained at more than 58.69cm.Therefore,we can optimize the allocation of vegetation structure on sandy land,optimize the allocation of conservation tillage measures on farmland,weaken the soil wind erosion in typical areas of northern North China,reduce the emission of soil dust,and protect the land productivity and atmospheric environment. |
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