Dust And Sand Releaseing Characteristics In Typical Shelter-belt Area Of Tuokexun County And Their Evaluation

The process of sand and dust release,i.e.,the process of surface sand and dust material breaking away from the surface under the action of wind,causes the smaller particulate matter in the soil to be lost by wind erosion.Sand and dust release affects the fertility of the soil and its ability to retain water,increases the content of respirable particulate matter in the air,and can directly or indirectly affect human activities.The study of sand and dust release has practical and theoretical significance for estimating the amount of sand and dust release,describing the mechanism of sand and dust storm occurrence,and formulating sand prevention and control measures.In order to study the sand and dust release characteristics of sand and dust events in the protection forest in Toxun County and evaluate the role of the protection forest in reducing the concentration of sand and dust released from the soil,this paper takes the typical protection forest area in Toxun County as the research object,and analyzes the relationship between vertical flux and loss flux and friction wind speed by observing the sand and dust events and deriving the images of friction wind speed and PM₁₀concentration changes;at the same time,it analyzes the relationship between sand transport flux and friction wind speed at different time scales and the difference of soil particle size between surface soil and wind eroded sediment after wind erosion process,and analyze the sand release characteristics.The main findings are as follows.（1）PM₁₀concentration during the dust release process will be significantly higher than the normal value,and the change of PM₁₀concentration at 100 cm is used to reflect the effect of frictional wind speed on the dust event.The PM₁₀concentration of dust events fluctuates with the fluctuation of the frictional wind speed,and the intensity of dust events becomes stronger when the frictional wind speed increases and weaker when the frictional wind speed decreases.（2）As the height from the ground increases,the effect of dust release on the variation of PM₁₀concentration becomes smaller.The correlation between vertical fluxes and loss fluxes is strong,and there is a strong consistency in reflecting dust release.The exponential function and power function are used to fit the data between the friction wind speed and sand loss flux at different time scales,and the variation law of sand loss flux with friction wind speed is more consistent with the law of exponential function.（3）The wind-eroded sediments collected in the trap-type sand collector were analyzed,and it was found that the content of the particle size fraction<0.063 mm and>0.5 mm was low;the content of the particle size fraction between 0.063 mm and 0.5 mm was high.（4）The values of mean particle size（M_Z）,sorting coefficient（S_d）,skewness value（S_k）and kurtosis value（K_u）of wind eroded sediments are larger than those of surface sediments,which is due to the occurrence of sandy events and the influence of wind erosion,the mean particle size of wind eroded sediments is larger,the sorting is worse,the particle size is more concentrated,and the wind eroded sediments are more sharp and narrow.（5）The surface wind erosion deposition fraction（D_P）of the control was significantly higher than thecontent of the protected forest area,and the sand and dust release was reduced by 21.5%in the wind protection forest compared to the control sample（bare sand）;and 59.3%in the farmland protection forest compared to the control sample（bare sand）.