Impacts of Vegetation and Climate Change on Dryland Rivers: Lesssons from the Rio Puerco, New Mexico

干旱的美国西部大部分水源依赖河流。来自人口增长、气候变化和入侵植物物种的压力，威胁着以传统上难以预见的方式改变该国的旱地河流、水资源和生态系统。对这些资源的可持续、适应性管理需要有能力预测它们对扰动的反应。由于未来的驱动因素很可能远远超出过去观察到的条件，因此建立基于过程的模型是至关重要的，这种模型可以在历史变化范围之外做出有用的、可转移的预测。然而，这种基于过程的模型的有效性只能通过与过去和现在行为的良好约束案例研究进行比较来证明。我们建议创建一个独特的新数据库，这将提供一个宝贵的机会来研究河流在几年到几十年的时间尺度上变化的原因和后果。新墨西哥州的里约热内卢Puerco盆地是西南地区研究最好、最具活力的盆地之一，为我们的分析提供了跳板。在过去的一个世纪里，里约热内卢Puerco及其洪泛平原在水文、产沙量和植被方面发生了重大变化。许多这些变化与20世纪20年代引进的外来树种柽柳及其随后在整个山谷网络中的传播有关。最近，对柽柳的破坏导致了河道几何形状和产沙量的巨大变化。因此，里约热内卢Puerco代表了长期植被变化对动态河流系统影响的独特自然实验。为了利用这一实验，我们建议建立并分析一个数据库，该数据库集成了历史流量和沉积物数据、河道横截面形式的时间序列测量、现代和历史植被模式、洪水沉积模式，以及来自激光雷达图像的近期河道变化的高分辨率测量。我们的分析包括两个时间尺度：(1)事件尺度，通过事件前后激光雷达处理大洪水的影响；(2)年代际尺度，重点关注20世纪30年代至今对红柳传播的响应。除了提供对河流变化的新见解外，综合数据库还将为科学界提供一个独特的平台，用于测试和完善下一代流量-沉积物-植被耦合模型。智力优势：旱地河流环境体现了洪水流量、河岸植被、河道几何、细泥沙侵蚀、水库淤积、河内渗透和水质之间的丰富反馈。通过在广泛研究的测试用例的上下文中探索系统，该项目将阐明这些反馈的性质和规模。该项目还将提供对假设的第一次检验，即有可能从基本原理计算旱地河流系统对每年到几十年的时间尺度上的水输入和植被覆盖的扰动的反应。更广泛的影响:该项目通过以下项目将研究、教育和推广紧密结合：(1)与K-12教师合作，将令人兴奋的河流动力学科学带入课堂；(2)让本科生和研究生参与跨学科研究；(3)通过开发和分发研究包进行更广泛的推广，其中包括水、沉积物和植被随时间变化趋势的数据分析练习。和模型动画，说明过程和反馈。我们还解决了一个重要的社会需求，即预测环境管理行动的潜在后果，例如最近引入的红柳叶甲虫作为生物防治剂。最后，我们将制作并发布一个详细的定量数据库，用于对未来模型进行基准测试，时间尺度从一次洪水事件到80年的河流转变。

Summary: The arid American West relies on rivers for much of its water. Pressures from population growth, climate change, and invasive plant species threaten to transform the nation's dryland rivers, their water resources, and their ecosystems in ways that have been traditionally difficult to foresee. Sustainable, adaptive management of these resources requires an ability to predict how they will respond to perturbations. Because future drivers are likely to reach well beyond the conditions that have been observed in the past, it is critical to have process-based models that can make useful, transferrable predictions beyond the historical range of variability. The validity of such process-based models can only be demonstrated, however, by comparison to well constrained case studies of past and present behavior. We propose to create a unique new database that will provide a valuable opportunity to study the causes and consequences of river transformation over time scales of years to decades. One of the best studied and most dynamic basins in the southwest, the Rio Puerco, New Mexico, provides the springboard for our analysis. Over the past century, the Rio Puerco and its floodplains have undergone major changes in hydrology, sediment yield, and vegetation. Many of these changes are linked with the introduction of the exotic tree species tamarix in the 1920s, and its subsequent spread throughout the valley network. More recently, efforts to destroy tamarix have led to dramatic changes in channel geometry and sediment yield. Thus, the Rio Puerco represents a unique natural experiment in the effects of long-term vegetation change on a dynamic fluvial system. To take advantage of this experiment, we propose to build and analyze a database that integrates historical flow and sediment data, time series measurements of channel cross-section form, modern and historic vegetation patterns, flood sedimentation patterns, and high-resolution measurement of recent channel change derived from lidar imagery. Our analysis encompasses two timescales: (1) the event scale, addressing the impact of a large flood with pre- and post-event lidar, and (2) the decadal scale, focusing on the response to tamarisk spread from 1930s to present. In addition to providing new insight into river transformation, the integrated database will provide the scientific community with a unique platform for testing and refining the next generation of coupled flow-sediment-vegetation models.Intellectual Merit: Dryland river environments embody a rich set of feedbacks among flood flow, riparian vegetation, channel geometry, fine-sediment erosion, reservoir siltation, in-stream infiltration, and water quality. By exploring the system in the context of an extensively studied test case, this project will illuminate the nature and magnitude of these feedbacks. The project will also provide a first test of the hypothesis that it is possible to compute, from basic principles, the response of a dryland river system to perturbations in water input and vegetation cover on annual to multi-decadal time scales.Broader Impacts: The project closely integrates research, education, and outreach through a program of (1) partnership with K-12 teachers in bringing the exciting science of river dynamics into the classroom, (2) involvement of undergraduate and graduate students in interdisciplinary research, and (3) broader outreach through development, and distribution of study packages that include data analysis exercises in water, sediment, and vegetation trends over time, and model animations that illustrate processes and feedbacks. We also address an important societal need to predict potential consequences of environmental management actions, such as the recent introduction of tamarisk leaf beetle as a biocontrol agent. Finally, we will produce and distribute a detailed, quantitative database for benchmarking future models, on time scales ranging from a single flood event to eight decades of river transformation.