Particle resuspension from leaf surfaces: Effect of species,leaf traits and wind speed

Particles deposited on leaf surfaces can be resuspended back into the atmosphere, thus generating pollution diffusion and hazarding to human health. The net amount of particles resuspended depends on leaf traits and weather conditions, such as speed wind and leaf roughness. However, little is known about the influence of leaf traits of different tree species on particle resuspension under certain conditions. In this study, we chose 6 typical greening tree species from Northeast China and focused on four-leaf traits: roughness, contact angle, stomatal density, and groove width. The wind tunnel was used to measure particle resuspension from leaf surfaces at different wind speeds (1, 2, 3 m/s) and test duration (10, 20, 30 min). Subsequently, we investigated the correlation between particle resuspension and leaf traits. The results indicated that Abies holophylla had the highest resuspension fraction (61.38%), followed by Salix babylonica (58.05%), Populus alba (54.21%), Juniperus chinensis (53.59%), and Pinus tabuliformis (50.51%), while Robinia pseudoacacia displayed the lowest particle resuspension fraction (32.02%). Particle resuspension rates of the tested species ranged from (8.24 ± 0.53) × 10⁻⁴/s to (2.65 ± 0.51) × 10⁻⁴/s, which was found to increase with wind speed enhancement and decrease with duration extension. With increasing the wind speed, the Pinus tabuliformis, and Juniperus chinensis were more efficient than Salix babylonica, and Populus alba in avoiding particle resuspension. Roughness and stomatal density were a significant negative correlation with particle resuspension rates, which demonstrates that the leaf surface traits can affect the particle resuspension process. Finally, our results suggest that the main factors influencing particle resuspension from leaf surfaces are wind speed, roughness, and stomatal density, which will provide a scientific foundation for pollution diffusion in future studies.     

Field evaluation of relationships between a vegetation structural parameter and sheltering against wind erosion

Measurements of natural vegetation canopies and of threshold friction velocities for soil movement were made at three arid and semiarid field sites. Threshold friction velocities for the vegetated surface and for bare soil were used to evaluate the partitioning of shear stress between that absorbed by the plant canopies and that absorbed by the soil surface (this potentially causing movement of soil particles). Canopy measurements were used to estimate lateral cover (total frontal-silhouette area per unit ground area), a parameter shown by previous laboratory studies to be a good predictor of shear stress partitioning. The relationship between lateral cover and shear stress partitioning for the field sites agreed with the laboratory results of Gillette and Stockton (1989). Results indicate that the protective influence of vegetative cover against wind erosion can be successfully predicted using simple measurements of vegetation canopy structure.     

基于PIV的渐变地表粗糙度对坡面流水动力特性的影响

粗糙度是影响坡面流水动力特性的关键因子,为探究渐变粗糙度影响下坡面流水力特性,采用粒子图像测速技术(particle image velocimetry, PIV)观测并分析3组流量下渐变粗糙床面下坡面流的流速轮廓线、紊动强度、雷诺应力和壁面切应力的变化规律。结果表明:(1)流速随粗糙度增加而减小;拟合无量纲流速得到流速分布对数公式,粗糙度增大与拟合常数A成反比,与积分系数B成正比。(2)渐变地表粗糙度流向紊动强度与光滑床面坡面流变化趋势相似。流向紊动强度随相对水深的增大而减小。随着粗糙度增大,流向紊动强度大小出现非显著性差异。渐变粗糙床面下流向紊动强度符合Nezu经验公式,流量与经验系数成正比。(3)不同流量下,渐变粗糙床面的雷诺应力分布与光滑床面相似。在粗糙度影响下,雷诺应力最大值出现在y/H=0.2~0.4处。随着粗糙度逐渐增加,壁面切应力逐渐增大。综合表明,增加PIV分辨率方法可以适用于坡面流水力特性的研究。探究渐变粗糙度对坡面流的影响,探讨坡面流水动力学特性,为水土保持理论研究提供新思路。