Collaborative Research: Quantifying feedbacks between fluvial morphodynamics and pioneer riparian vegetation in sand-bed rivers

在动态河流生态系统中，河岸植被与水流、泥沙输移和沉积相互作用，导致河道形态和植被群落的共同进化。该项目将对沙床河流中植被和河道过程之间的相互作用和反馈进行机械性和预测性的理解。该项目解决了两个广泛的问题：(1)木本植物如何单独和共同影响水流和泥沙输送；(2)水流和泥沙输送过程如何影响具有不同形态特征的河岸植物的死亡？综合实验室、现场和计算方法将被用来表示不同尺度的空间、时间和生态系统复杂性。水槽和中游实验将测试植被对单个植物周围和植被斑块内的水流和泥沙运移的影响，以及水流对通过冲刷和掩埋去除植物的交互作用。此外，明尼苏达大学室外河流实验室将用于测试植被斑块与水深、水流和泥沙在蜿蜒的沙床河道中的传输之间的反馈。在亚利桑那州西部比尔·威廉斯河受管制的沙床河段进行的实地调查，将结合大坝控制洪水事件前后的高分辨率地形和植被测量以及水力和泥沙流量的高流量测量。最后，将使用计算模型来综合和概括实地工作。二维水流和泥沙模型将在模拟水流和植被管理情景的同时评估反馈，其中植被效应是基于实验室和野外观测进行参数化的。此外，河岸植被斑块动态模型将被用来分析物种在多个世代之间冲刷和埋葬死亡率差异的社区层面的影响。这项调查将增进我们对河流沿线物理过程和植被群落共同进化的了解，并将为河流恢复和管理工作提供信息。这项研究将专门讨论与设计大坝泄水以造福生态系统有关的问题。它将探索大坝下游泥沙供应的减少如何影响河岸植被，并将研究棉杨和柳树的死亡机制，这两种植物是许多半干旱地区河流沿线的优势物种和重要的生态物种。它还将帮助管理罗望子，这是一种入侵灌木，流行于美国西部的河流沿线。通过整合新的实验设施、实地研究区域和建模方法，该项目将提高我们理解和管理河流生态系统的能力。

In dynamic river ecosystems, riparian vegetation interacts with flow, sediment transport, and deposition, resulting in the coevolution of channel forms and vegetation communities. This project will develop a mechanistic and predictive understanding of interactions and feedbacks between vegetation and stream-channel processes in sand-bed rivers. The project addresses two broad questions: (1) how do woody plants affect flow and sediment transport individually and collectively, and (2) how do flow and sediment transport processes influence the mortality of riparian plants with different morphological traits? Integrated laboratory, field, and computational approaches will be employed to represent varying scales of space, time, and ecosystem complexity. Flume and mesocosm experiments will test the effect of vegetation on flow and sediment transport around individual plants and within vegetation patches, and the reciprocal effect of flow on plant removal via scour and burial. In addition, a field-scale experimental facility, the Outdoor Stream Lab at the University of Minnesota, will be used to test feedbacks between vegetation patches and bathymetry, flow, and sediment transport in a meandering sand-bed channel. Field investigations in a regulated, sand-bed reach of the Bill Williams River in western Arizona with a mixed native and invasive riparian community will combine high-resolution measurements of topography and vegetation before and after dam-controlled flood events with high-flow measurements of hydraulics and sediment flux. Finally, computational modeling will be used to synthesize and generalize field efforts. Two-dimensional flow and sediment modeling, in which vegetation effects are parameterized based on laboratory and field observations, will evaluate feedbacks while simulating flow and vegetation management scenarios. In addition, a riparian vegetation patch-dynamics model will be adapted to analyze community-level implications of species' differences in scour and burial mortality over multiple generations. This investigation will advance our knowledge of the co-evolution of physical processes and vegetation communities along rivers and will also inform river restoration and management efforts. This study will specifically address questions related to designing water releases from dams to benefit ecosystems. It will explore how reductions in sediment supply downstream of dams affect riparian vegetation and it will examine the mortality mechanisms of cottonwood and willow, which are dominant and ecologically important species along rivers in many semi-arid regions. It will also aid in the management of tamarisk, an invasive shrub that is prevalent along rivers in the western United States. By integrating novel experimental facilities, field study areas, and modeling methods, the project will advance our ability to understand and manage fluvial ecosystems.