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。在陡峭的查帕拉尔地区发生火灾后，往往会发生灾难性的泥石流。由于这种威胁，另一个潜在的重大火灾后侵蚀过程，风蚀，一直没有得到重视。从南加州的一个被烧毁的地区的观察表明，风蚀可能是一样重要的径流侵蚀在烧毁的半干旱景观。虽然保护土壤表面不受风影响的植被的清除无疑在燃烧地区的风蚀率较高方面发挥了作用，但土壤本身内部由火灾引起的变化可能在增加土壤对风成搬运的脆弱性方面更为重要。未受干扰的查帕拉尔土壤被生物垫覆盖，这是一个由藻类、地衣和苔藓覆盖的查帕拉尔细根组成的密集网络，它的作用是保护下面的土壤。然而，严重的火灾似乎会燃烧生物垫，使土壤暴露在风中。在南加州，大火通常是由圣安娜风驱动的，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，被大火烧焦的地区随后会遭受长达数月的大风。实地观察和卫星图像证明，在这些条件下，风蚀率极高。本项目将通过风洞实验研究火、生物垫和风蚀之间的关系。从查帕拉尔山坡上采集的未受干扰的土壤表面样本将在实验室中受到受控野火条件的影响，以模拟不同温度和持续时间的火灾。然后将这些样品放在风洞中测定它们的临界摩擦速度，这是衡量土壤被风侵蚀的一个指标。该项目的主要影响将是提供有关南加州空气中尘埃来源的信息，这些尘埃可能影响人类健康。它应该对其他地方的许多类似环境产生影响。据估计，空气中的灰尘污染是加州每年数千人过早死亡的原因;卫星图像显示，在圣安娜天气期间，燃烧区是向西吹到洛杉矶地区的灰尘的重要来源。该项目的目标之一是建立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。该项目还将为少数群体服务机构的一名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.