Vegetative Roughness Controls on Aeolian Sediment Transport

干旱地区植被的类型和分布对风沙输沙系统的启动和沙尘通量的大小起着至关重要的控制作用。尽管有这些知识，在目前的区域风蚀模型中没有很好地考虑到自然植被的作用。以往的研究表明，大型固体不可蚀性粗糙度元素引起的输沙率变化是这些元素大小和分布的函数。对于植被而言，其特性（如孔隙度、柔韧性、阻力系数、分布等）造成了不确定性，即它们的影响与固体单元粗糙度的相似程度如何，这在当前的风蚀模型中通常是假设的。本项目将通过实地实验研究植物群落结构的分布模式和相关的空气动力学特性如何影响风对沙粒的输送。回答这些问题所需的数据将在美国农业部乔丹实验范围（JER）内的四个地点收集，那里的景观已经从以草地为主转变为以灌木为主，结果是风蚀和土地退化增加。这四个站点代表了豆科植物在JER的不同入侵阶段，每个站点的仪器将测量区域和当地的风速、地面剪应力、沙尘运动和植被分布特征。这项研究将有助于确定植被的关键特征，这些特征可用于指示稳定性或接近随后导致风蚀和环境退化增加的临界阈值。该项目的结果将为更准确地量化稀疏植被对输沙阈值和沙通量的影响提供一种手段，可将其纳入区域风蚀模型。这项研究的目的是增加我们对沙漠环境中风沙运输过程和植被之间联系的理解。世界范围内的沙漠环境正面临着气候变化、人口增长及其对资源需求的压力。植被在沙漠环境的稳定中起着至关重要的作用，特别是作为防止风蚀和经常相关的粉尘排放过程的缓冲。然而，在美国西南部奇瓦瓦沙漠的部分地区，一些沙漠植物群落凭借其生存机制，可以加剧风蚀，导致环境下降。因此，植被可以对风蚀过程产生积极和消极的影响，本项目的结果将有助于确定在各种环境条件下这些影响的性质和程度。这些知识随后可以用来帮助评估气候变化和人为压力如何加剧这些敏感地区的退化。

The type and distribution of vegetation in arid environments play a critical role in controlling the initiation of the wind-driven sediment transport system as well as the magnitude of the flux of sand and dust. Despite this knowledge, the role of natural vegetation is not well accounted for in present regional wind erosion models. Previous research indicates that the change in sand transport rate due to large solid non-erodible roughness elements is a function of both the size and the distribution of the elements. For vegetation its properties (e.g., porosity, flexibility, drag coefficients, distribution, etc.) create uncertainty as to how similar their effects are as compared to solid element roughness, which is typically assumed in current wind erosion models. This project will investigate through field-based experimentation, how plant community structure as characterized by its distribution pattern and associated aerodynamic properties affects sand transport by wind. The data needed to answer these questions will be collected at four sites within the USDA Jornada Experimental Range (JER), NM, where the landscape has changed from one dominated by grasslands to one that is becoming dominated by shrubs, with a resultant increase in wind erosion and land degradation. The four sites represent different stages of mesquite invasion at the JER. At each of the sites instruments will measure regional and local wind speeds, surface shear stresses, sand movement activity, and the vegetation distribution characteristics. This research will aid in the identification of key characteristics of vegetation that can be used to indicate either stability or the approach of a critical threshold that subsequently leads to an increase in wind erosion and environmental degradation. The results from this project will provide a means to more accurately quantify the effect of sparse vegetation on sediment transport thresholds and sand fluxes, which can be incorporated into regional wind erosion models.This research is designed to increase our understanding of the links between wind-driven sediment transport processes and vegetation in desert environments in general. Desert environments worldwide are under pressure from climate change as well as expanding populations and their need for resources. Vegetation plays a critical role in the stability of desert environments, specifically as a buffer against wind erosion and the often-associated dust emission process. However, as evident in parts of the Chihuahuan desert in the U.S. southwest some desert plant communities, by virtue of their survival mechanisms, can exacerbate wind erosion, leading to environmental decline. Vegetation can therefore both positively and negatively influence wind erosion processes and the results of this project will aid in determining the nature and degree of these influences under a variety of environmental conditions. Such knowledge can subsequently be used to aid in evaluating how climate change and human-induced pressures could exacerbate degradation in these sensitive areas.