半湿润区农田风蚀物垂直分布特征

The Vertical Distribution Characteristics of Farmland Wind-erosion Dust over Semi-humid Region

通过两种观测手段对半湿润区农田风蚀物垂直分布特征进行了研究。结果表明,半湿润区农田风蚀强度较弱,风蚀物颗粒较细,主要由极细沙和粉沙组成。风蚀物含量垂向分布遵循幂函数递减规律,反映了以悬移质为主的风沙流结构特征。农田地表特征、风速和粒级等因素均对风沙流结构具有显著影响。农田风蚀强度大小影响风蚀物在近地表的分布规律。风速增大使相对输沙量在近地表增加,上层减少。风蚀物粒级越大,则输沙量沿垂直方向递减的幅度愈大。随着高度增加,风蚀物各粒级含量中砂级组分含量减少,粉砂及粘土组分含量增加,风蚀物粒径变细,粒径范围不断收窄。最大粒径和平均粒径沿垂直方向的变化都服从指数函数递减规律。

Observation of the vertical distribution characteristics of farmland wind-erosion dust over semi-humid region using two methods showed that the wind-erosion in semi-humid region was weak and the wind-erosion dust which mainly composed of extremely fine sand and silt was thin.The power decreasing rule of wind-erosion dust changing in vertical direction had reflected the wind-sand flow feature of primarily comprising of Suspended sediment.The wind-sand flow structure was influenced remarkably by the farmland surface condition,wind speed and dust grade.The farmland wind-erosion intensity had an influence on the changing rule of wind-erosion dust near surface;The wind speed increasing had made an relatively arising of sand transporting percentage in near surface and a reducing upward;The decreasing scope of sand transporting in vertical direction was adding with the increasing of sand size.With increasing height,the percent of sand decreases,but the percent of silt and clay increases,the wind-erosion particle size became thin,and the particle size spectrum squeezed.The vertical distribution of maximum and average particle size followed the descending law of index function.