Doctoral Dissertation Research: Multi-Scalar Geomorphic and Vegetative Feedbacks in the Colorado River Basin

最近，利用地貌模型的新研究表明，河岸植被在单线通道的形成和维持中起着重要作用。了解什么样的地貌，水力和水文条件促进入侵河岸植物是至关重要的，这些模型的发展。 博士生丽贝卡·曼纳斯在州立大学犹他州流域科学教授约翰·施密特的指导下，将研究河岸植被和地貌过程之间的相互作用。研究设计利用了科罗拉多河流域独特的地理和地貌，以及丰富的已发表研究和长期水文和物理数据集。了解地貌-植被相互作用的易处理的尺度是小尺度，其中水力和沉积环境可以被描述和量化。为了解释这些过程在更大尺度上的表达，本研究采用了多标量方法。选择了科罗拉多河流域的四个河段，以获取水文、气候和沉积控制的梯度，以及流域中的塔马克入侵和水文变化的时间差异。这些河段用于描述河道形态和河岸植被之间的相互作用，以确定由物理驱动因素（水文和沉积物供应）和河岸植被（tamelik入侵）变化引起的河道变化的幅度。洪泛区地层学和2-D流动建模的代表性地貌表面内的四个达到将被用来描述和量化如何入侵的非本地河岸植物引起的正反馈，导致加速率的通道变窄。流动建模作为一种工具，在检查植被/地貌反馈的准确性将取决于空间上精确的表征的水力粗糙度的各种植物群落在不同的生命阶段。粗糙度参数化将在一个单一的物种（tamarak）的生活史进行检查。我们的能力作出预测，在地貌信道响应扰动仍然容易出错，有很大的不确定性，因为无法充分描述是什么决定了信道的形状和大小。 这是一个关键问题，在科罗拉多河流域在这一时期的快速气候变化，因为这个地区是敏感的积雪过程，是主要来源的流域高水的需求。 认识到河道变化会影响水生和河岸物种，并改变河流环境的娱乐价值，国家公园管理局（National Park Service）表示有兴趣确定在环境条件改变的情况下，河道将在何处以及如何发生变化。这项研究的结果不仅有助于分离和识别哪些环境变量促成了河道变化，从而进一步推动地理科学，而且有助于向管理人员提供有关科罗拉多河流域管理的信息。具体而言，这项研究将致力于回答有关河流系统的哪些区域对水文变化和非本地植物物种入侵最敏感的问题，以及入侵植物物种的生活史何时会有效地改变河道的形状。

New research using geomorphological models has recently shown that riparian vegetation plays a significant role in the formation and maintenance of single-thread channels. Knowing what geomorphic, hydraulic and hydrologic conditions promote invasive riparian plants is critical to the development of these models. Doctoral student Rebecca Manners, under the guidance of Professor John Schmidt in watershed sciences at Utah State University will examine the interactions between riparian vegetation and geomorphic processes at the field scale. The study design takes advantage of the unique geography and geomorphology of the Colorado River basin and its abundance of published studies and long-term hydrologic and physical datasets. The tractable scale of understanding geomorphic-vegetation interactions is the small scale, where the hydraulic and depositional environments can be described and quantified. To account for the expression of these processes at the larger-scale, this study takes a multi-scalar approach. Four reaches of the Colorado River basin have been chosen to capture the gradient of hydrologic, climatologic, and sedimentologic controls, as well as the difference in timing of tamarisk invasion and hydrologic alteration in the watershed. These reaches are used to describe the interactions between channel form and riparian vegetation to determine the magnitude of channel change caused by changes in physical drivers (hydrology and sediment supply) and riparian vegetation (invasion of tamarisk). Floodplain stratigraphy and 2-D flow modeling of representative geomorphic surfaces within each of the four reaches will be used to describe and quantify how the invasion of non-native riparian plants induces a positive feedback that causes accelerated rates of channel narrowing. The accuracy of flow modeling as a tool in examining vegetation/geomorphic feedbacks will depend on spatially precise characterization of the hydraulic roughness of various plant communities at different life stages. Roughness parameterization will be examined over the life-history of a single species (tamarisk). Our ability to make predictions in geomorphology about channel response to perturbations remains error prone with much uncertainty because of the inability to adequately describe what determines channel shape and size. This is a critical issue in the Colorado River Basin during this period of rapid climate change because this region is sensitive to snow accumulation processes that are the primary source of the basins high water demand. Recognizing that channel changes impact aquatic and riparian species as well as alter the recreational value of the river setting, the National Park Service (NPS) has expressed an interest in identifying where and how channels will change provided altered environmental conditions. Results from this research will not only further geographic science by helping to isolate and identify which environmental variables have contributed to channel changes, but also help inform managers regarding management of the Colorado River basin. Specifically, this research will work towards answering questions regarding which areas of a river system are most sensitive to hydrologic changes and invasion by non-native plant species and when in the life-history of an invasive plant species does it become effective in altering the shape of the channel.