Temporal Change Of Soil Wind Erodibility And Its Impact For Sand Flux On Farmlands

Hebei Bahang area is the key area for wind erosion prevention and control in the north of our country.It is very important to scientifically understand the law of soil wind erosion in the Bahang area.The dynamic change of soil wind erodibility and its effect on near-surface aeolian sand transport is the key to understand the process of wind erosion.Soil wind erodibility refers to the sensitivity of soil to wind-induced stripping and transport damage in the process of wind erosion events,tillage measures,meteorological and climate factors.At present,there is a lack of systematic research on the dynamic changes of soil wind erosion at different time scales and its relationship with sediment transport rate.In this paper,soil erosion degree（EF）and dry-soil aggregate stability（DASt）were used as indexes of soil wind erodibility.The dynamic changes of soil wind erodibility in Bashang area were discussed under three time scales,namely wind erosion season,tillage wind erosion period and wind erosion event.Combined with the measured data of 5min time scale,the influence of soil wind erosion on near-surface aeolian sand transport was further explored.The main research conclusions are as follows:According to the change characteristics of surface wind erosion,the wind erosion season can be divided into four stages:autumn wind erosion stage,winter wind erosion stage,freeze-thaw alternating wind erosion stage and spring wind erosion stage.The spring wind erosion stage is the highest,the winter and spring alternating freeze-thaw phase has the least erosion.By comparing the wind erosion of farmland,woodland and grassland during the cultivation period in spring,it is shown that the surface soil stability was poor and it was prone to wind erosion.It was found that the relative content of dry aggregates particles in the range of 0.425～0.85 mm and 0.106～0.25mm decreased and that of dry aggregates particles in the range of 0.85～5 mm increased under strong wind erosion.In the range of 0.25-0.425 mm,the relative content of dry aggregates particles changed little.In the process of wind erosion,the wind erosion erodibility of soil decreases,and the sand transport rate also decreases,indicating that the change of soil wind erosion erodibility in winter has a significant effect on the sand transport rate.The Fryrear model was used to fit the 5 min changes of wind sand flux at height of 5 cm near the surface,and the influence of wind erodibility on the changes of sand flux along the surface was discussed combined with the friction wind velocity（u_*）.It is found that the saturated sediment transport rate(f_max)and u_*conform to the power function relationship,and the development of saturated path length(L_sat)does not depend on u_*.Under similar u_*conditions,the development and change of f_maxand L_satare obviously fluctuating,which may be related to the dynamic change of wind erodibility.This research is helpful to the theoretical understanding and practical application of wind erosion and provides a technical reference for the development of process wind erosion model in our country.