植被盖度对风沙流结构及输沙率的影响

The influence of vegetation coverage on the wind sand flow structure and sediment transport rate

土壤风蚀是全球干旱和半干旱地区生态环境安全的重要威胁。植被通过降低风速和捕获土壤颗粒能够有效地降低土壤风蚀发生的风险。目前,人们对于植被控制土壤风蚀的最优格局和盖度的理解仍然有待深入。借助野外移动风洞,测量了地表输沙率和风沙流结构对草本植物沙打旺(Astragalus adsurgens)盖度的响应程度。结果表明:(1)当植被盖度较小时,风沙流结构的分布曲线遵循指数函数分布规律,随着植被盖度增大,其曲线形态变化差异大。(2)植被覆盖能够有效地降低土壤输沙率并抬高风沙输移发生的高度。(3)地表空气动力学粗糙度与植被盖度服从对数函数变化规律,其增长率随植被盖度的增大而逐渐减小并最终趋于零,下垫面空气动力学粗糙度存在阈值现象。(4)沙打旺控制土壤风蚀的最佳盖度约为30%,能够有效地抑制20 cm高度以下约90%的风蚀量。

Soil wind erosion is an important threat to the global ecological and environmental security of arid and semi-arid area.Vegetation can effectively reduce the risk of soil wind erosion by reducing wind speed and capturing soil particles.At present,people's understanding of the optimal pattern and coverage of vegetation controlling soil wind erosion still needs to be deepened.With the help of a mobile wind tunnel in the field,this article measured the response of surface sediment transport rate and wind sand flow structure to the coverage of herbaceous plants(Astragalus adsurgens).The results show that:(1)When the vegetation coverage is small,the distribution curve of wind sand flow structure follows the exponential function distribution law.With the increase of vegetation coverage,the curve shape appears differentiation.(2)Vegetation coverage can effectively reduce the intensity of soil wind erosion and raise the height of sand transport.(3)The surface aerodynamic roughness and vegetation coverage follow a logarithmic function variation law,and their growth rate gradually decreases and eventually approaches zero with the increase of vegetation coverage.There is a threshold phenomenon in the aerodynamic roughness of the underlying surface.(4)The optimal coverage of Astragalus adsurgens for controlling soil wind erosion is about 30%,which can effectively suppress about 90%of wind erosion below a height of 20 cm.