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

最近利用地貌模型进行的新研究表明，河岸植被在单线河道的形成和维护中发挥着重要作用。了解哪些地貌、水力和水文条件促进了河岸植物入侵，对这些模型的发展至关重要。博士生丽贝卡·曼纳斯将在犹他州州立大学流域科学教授约翰·施密特的指导下，研究河岸植被和野外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，以及其丰富的已发表研究和长期水文和物理数据集。了解地貌-植被相互作用的容易处理的尺度是小尺度，在这里可以描述和量化水力和沉积环境。为了解释这些过程在更大范围内的表达，本研究采用了多标量方法。科罗拉多河流域的四个河段被选择来捕捉水文、气候学和沉积学控制的梯度，以及该流域罗望鱼入侵和水文变化的时间差异。这些河段被用来描述河道形态和河岸植被之间的相互作用，以确定物理驱动因素(水文和泥沙供应)和河岸植被(罗望鱼入侵)变化引起的河道变化的幅度。河滩地层学和四个河段内具有代表性的地貌面的二维流模型将被用来描述和量化非本地河岸植物的入侵如何引起正反馈，从而加速河道收窄的速度。作为研究植被/地貌反馈的一种工具，水流模拟的准确性将取决于对不同生命阶段各种植物群落水力粗糙度的空间精确表征。粗糙度参数将在单一物种(罗望子鱼)的生命史上进行检验。由于不能充分描述是什么决定了河道的形状和大小，我们在地貌学中预测河道对扰动的响应的能力仍然容易出错，具有很大的不确定性。在这段快速气候变化时期，这是科罗拉多河流域的一个关键问题，因为该地区对积雪过程非常敏感，而积雪过程是流域高用水需求的主要来源。认识到河道改变影响水生和河岸物种以及改变河流环境的娱乐价值，国家公园管理局(NPS)表示有兴趣确定在环境条件改变的情况下，河道将在哪里改变以及如何改变。这项研究的结果不仅有助于分离和识别哪些环境变量导致了河道变化，从而进一步促进了地理科学，而且还有助于向管理人员提供有关科罗拉多河流域管理的信息。具体地说，这项研究将致力于回答以下问题：河流系统的哪些区域对水文变化和非本地植物物种的入侵最敏感，以及在入侵植物物种的生活史中，什么时候它在改变河道形状方面变得有效。

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.