Earth, Wind, and Fire: Eolian Erosion in Burned Chaparral Landscapes

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。在陡峭的灌木丛中发生的火灾往往伴随着灾难性的泥石流。由于这种威胁，另一个潜在的重要的火灾后侵蚀过程，风蚀，一直没有得到重视。来自南加州一个被烧毁地区的观察表明，在被烧毁的半干旱地区，风蚀可能与径流侵蚀一样重要。尽管保护土壤表面不受风影响的植被的消失无疑在烧伤地区更高的风蚀率中发挥了作用，但火灾引起的土壤本身的变化在增加土壤对风成运输的脆弱性方面可能更为重要。未受干扰的灌木林土壤覆盖着一层生物垫，这是一种由茂密的灌木林根系组成的网络，上面覆盖着藻类、地衣和苔藓，起到保护下面土壤的作用。然而，高强度的火灾似乎烧毁了生物垫，使土壤暴露在风中。在南加州，大火通常是由圣安娜风引起的，这种风可以达到飓风的速度。由于这些风的条件通常发生在9月至3月，因此被大火烧焦的地区随后会遭受数月的大风。实地观测和卫星图像证明在这些条件下风蚀率极高。这个项目将通过风洞实验来研究火、生物垫和风蚀之间的关系。从灌木林山坡上收集的未受干扰的土壤表面样本将在实验室中受到控制的野火条件的影响，以模拟不同温度和持续时间的火灾。然后，这些样品将被放置在一个风洞中，以确定它们的阈摩擦速度，这是衡量土壤受风侵蚀能力的一种指标。该项目的主要影响将是提供可能影响南加州人类健康的空气粉尘来源的信息。它应该对其他地方的许多类似环境有所启示。据估计，在加州，空气中的粉尘污染每年导致数千人过早死亡；卫星图像显示，在圣安娜飓风的情况下，被烧毁的地区是向西吹到洛杉矶地区的重要沙尘来源。该项目的目标之一是开发易于测量的土壤参数与风蚀潜力之间的关系，供空气污染控制区使用。该项目还将为一名来自少数民族服务机构的本科生提供教育机会。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Fires in steep chaparral landscapes are often followed by catastrophic debris flows. Because of this threat, another potentially significant post-fire erosional process, wind erosion, has been under-appreciated. Observations from a burned area in Southern California suggest that wind erosion may be as important as runoff erosion in burned semi-arid landscapes. Although the removal of vegetation, which protects the soil surface from the wind, undoubtedly plays a role in higher rates of wind erosion from burned areas, fire-induced changes within the soil itself may be more important in increasing the vulnerability of the soil to eolian transport. Undisturbed chaparral soils are covered by a biotic mat, a dense network of fine chaparral roots overlain by algae, lichen, and moss, which acts to armor the soil underneath. High severity fires, however, appear to combust the biotic mat, leaving the soil exposed to the wind. In Southern California, large fires are often driven by Santa Ana winds that can reach hurricane speeds. Because the conditions for these winds generally occur from September to March, the areas scorched by fire are then subjected to high winds for many months. Field observations and satellite images testify to extreme rates of wind erosion under these conditions. This project will investigate the relationship between fire, the biotic mat, and wind erosion through a program of wind-tunnel experiments. Undisturbed soil surface samples, collected from chaparral hillslopes, will be subjected to controlled wildfire conditions in the laboratory to simulate fires of varying temperatures and durations. The samples will then be placed in a wind tunnel to determine their threshold friction velocity, a measure of the soil's erodibility by wind.The main impact of this project will be to provide information on a source of airborne dust that can affect human health in Southern California. It should have implications for many similar environments elsewhere. It has been estimated that airborne dust pollution is responsible for thousands of premature deaths annually in California; satellite images indicate that burned areas are important sources of dust blown westward to the Los Angeles area during Santa Ana conditions. One of the goals of this project is to develop relationships between easily measured soil parameters and wind erosion potential for use by air pollution control districts. This project will also provide an educational opportunity for an undergraduate student from a minority-serving institution.