Vegetative Roughness Controls on Aeolian Sediment Transport

干旱环境中植被的类型和分布对控制风生泥沙输送系统的启动以及沙尘通量的大小起着关键作用。尽管有这些知识，但在目前的区域风蚀模型中，自然植被的作用并没有得到很好的解释。以往的研究表明，大尺寸固体不可侵蚀粗糙度元素引起的输沙率变化是元素大小和分布的函数。对于植被，其特性(例如孔隙度、灵活性、阻力系数、分布等)不确定它们的影响与固体元素粗糙度相比有多相似，后者在当前的风蚀模型中通常被假定。本项目将通过野外实验，研究以植物群落分布格局和相关空气动力学特性为特征的植物群落结构如何影响风沙输送。回答这些问题所需的数据将在新墨西哥州USDA Jornada实验场(JER)内的四个地点收集，那里的景观已经从以草原为主转变为以灌木为主，导致风蚀和土地退化增加。这四个地点代表了JER麦斯奎特入侵的不同阶段。在每个地点，仪器将测量区域和当地的风速、地表切应力、沙粒移动活动和植被分布特征。这项研究将有助于确定可用来指示稳定性或接近导致风蚀和环境退化增加的临界阈值的植被的关键特征。这项研究的结果将为更准确地量化稀疏植被对泥沙输移阈值和沙通量的影响提供一种手段，可以被纳入区域风蚀模型。这项研究旨在增加我们对沙漠环境中风生泥沙输送过程和植被之间的联系的理解。世界各地的沙漠环境正受到气候变化以及不断扩大的人口及其对资源的需求的压力。植被在沙漠环境的稳定性中发挥着关键作用，特别是作为抵御风蚀和经常伴随的粉尘排放过程的缓冲。然而，正如美国西南部奇瓦瓦沙漠的部分地区所表明的那样，一些沙漠植物群落凭借其生存机制，可能会加剧风蚀，导致环境退化。因此，植被对风蚀过程既有积极的影响，也有消极的影响，该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。这些知识随后可用于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.