Collaborative Research: Characterizing controls on postfire steepland ravel - when does bioturbation go too far for diffusive models?

山火过后，山坡上的土壤会变得不稳定，容易受到侵蚀。这种侵蚀发生的一种方式是通过一种被称为干沉降的过程，在这种过程中，植被的焚烧或动物的干扰导致沉积物颗粒反弹、滚动并滑下山坡。在许多陡峭的景观中，ravel是火灾后侵蚀的主要形式，可以为火灾后的泥石流等危险提供材料。目前迫切需要火灾后侵蚀和灾害预测模型，以便为应对当今不断变化的野火状况提供信息，但目前常用的沉积物运输规律无法解释破坏过程，这阻碍了它们的发展。该项目将通过直接测量最近在加州被野火烧毁的山坡上的沉积物运动来推进对ravel侵蚀过程的理解。由此产生的过程知识将使我们能够更好地模拟侵蚀和灾害，以应对野火等干扰，以及更好地估计由于野火条件的预测变化而导致的长期侵蚀。主要研究人员还将与当地教育工作者合作，开发一个新的外展项目和材料，为来自STEM（科学、技术、工程和数学）领域历史上代表性不足的弱势群体的K-12学生提供真实的实地研究经验，同时改变人们对户外体验和地球科学职业的看法。本研究将使用短寿命放射性核素分析、高分辨率地形数据和物理测量的新组合来校准和进行关于自然沉积物输运的卷积沉积物通量模型的首次现场测试。这项工作将验证这样一个假设，即在新燃烧的陡坡上的关键条件下，穴居动物的干扰可以携带以重尾粒子移动距离分布为特征的沉积物通量，从而逃避扩散的、基于连续体的模型的表示。这项研究将1)开创一种新的方法来推断拉威尔沉积物的粒子历史；2)记录自然粒子携带速率、移动距离和通量的统计数据，以研究它们与随时间演变的控制物理变量的函数关系；3)论证非局部输沙模型的实用性并确定用例场景；4)提供关于地貌和生物过程之间的连通性如何影响动态响应的见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

After a wildfire, soils on hillsides can be destabilized and subject to elevated risk of erosion. One way this erosion occurs is through a process known as dry ravel, in which the incineration of vegetation or disturbance by animals causes sediment particles to bounce, roll, and slide down the hillslope. In many steep landscapes, ravel is the primary form of erosion after fires and can supply material to post-fire hazards like debris flows. Post-fire erosion and hazard prediction models are urgently needed to inform responses to today’s changing wildfire regime, but they are currently hindered by the inability of commonly used sediment transport laws to account for ravel processes. This project will advance understanding of ravel erosion processes by directly measuring sediment movement on hillslopes that were recently burned by wildfires in California. The resulting process knowledge will enable better modeling of erosion and hazards in response to disturbances like wildfire, as well as better estimates of long-term erosion due to predicted changes in wildfire conditions. The principal investigators will also collaborate with local educators to develop a new outreach program and materials to provide authentic field research experiences to underprivileged K-12 students from groups historically underrepresented in STEM (science, technology, engineering, and mathematics), while shifting perceptions around outdoor experiences and geoscience careers.This study will use a novel combination of short-lived radionuclide analysis, high-resolution topographic data and physical measurements to calibrate and conduct the first field test of a convolutional sediment flux model on natural sediment transport. This work will test the hypothesis that, under key conditions in newly burned steeplands, disturbance by burrowing animals can entrain sediment fluxes characterized by heavy-tailed particle travel distance distributions, thereby escaping representation by diffusive, continuum-based models. This study will 1) pioneer a new methodology for inferring particle histories from ravel deposits; 2) document statistics on natural particle entrainment rates, travel distances and fluxes to investigate their functional relationships with controlling physical variables that evolve over time; 3) demonstrate the utility and identify use-case scenarios for nonlocal sediment transport models; and 4) provide insight on how connectivity between geomorphic and biotic processes informs dynamic responses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.