Doctoral Dissertation Research: Interactions Between a Native Sedge (Carex nudata) and Physical River Processes: A Model of Coupled Biogeomorphic Development

河流恢复目前是整个西海岸大量投资的重点，其动机是迫切需要改善受威胁的太平洋鲑鱼种群的栖息地。这项研究将有助于这些努力：草苔，一种遍布西海岸的原生莎草，越来越被认为是恢复目标的促进者，但土地和河流管理者对它如何改变河道形态以及哪些环境变量对其生存能力至关重要缺乏清晰的认识。本研究探讨了滨水莎草C. nudata与河流环境之间的相互作用。这项研究的独特之处在于它旨在研究这种关系的两个方面：河流的物理环境和流动模式如何驱动C. nudata分布，以及C. nudata随后如何改变河流的物理过程。C. nudata引起了中福克约翰戴河调查人员的注意，在河岸放牧的牛撤离后，该病毒大量爆炸。C. nudata沿着低流道的边缘生长，在砾石坝上，在切割的河岸底部和岛屿上，其茂密的根系使其能够承受强烈的水流。C. nudata似乎以增加河流复杂性的方式改变河道形态，从而改善鱼类栖息地，促进河流恢复目标。研究人员假设，裸草促进了复合通道的进化，其中裸草稳定了狭窄的低流量通道，但与许多植物不同，裸草不能减缓被切割的河岸的侵蚀，从而使河岸通道继续移动或变宽。在某些情况下，这一过程被假设会导致位于河岸底部的C. nudata斑块“分离”并成为岛屿，从而产生多线程通道。研究人员将使用多种方法来检验这些假设。将使用反复的地形测量和侵蚀销钉检查河岸后退和河床侵蚀/淤积的变化。银行撤退和岛屿编队也将检查与航空图像。流速模式可以解释侵蚀/沉积模式，将用声学多普勒电流剖面仪进行检查。关于裸藻的分布，研究者假设裸藻的分布模式受水文变量和沉积物类型的驱动。这些假设将通过在三个不同的河流流域对C. nudata进行从源头到口的调查来检验。直到20世纪后半叶，河流地貌学只关注河流过程的物理维度。直到最近，人们才认识到植被对河流的形状和形态有重大影响（Hughes 1997）。然而，目前对植物-河流相互作用的研究通常集中在这种关系的一个方面：即河流环境对植物群落的影响或植物对某些物理过程的影响。Corenblit等人（2007）强调植物与河流关系的互惠性，并提出了生物地貌演替的概念来描述河流形状和形态与河岸植物群落的联系发展。

River restoration is currently the focus of enormous investment throughout the West Coast, motivated by the imperative to enhance habitat for threatened Pacific salmon populations. This research will contribute to these efforts: Carex nudata, a native sedge that occurs throughout the West Coast, is increasingly perceived as a facilitator of restoration goals, but land and river managers lack a clear understanding of how it may alter channel morphology and what environmental variables are critical to its viability. The proposed research explores the interactions between C. nudata, a riparian sedge, and its river environment. The research is distinguished by its aim to examine both sides of this relationship: how the river's physical environment and flow patterns drive C. nudata distribution, and how C. nudata then alters the physical processes of the river. C. nudata caught the attention of investigators in the Middle Fork John Day River where it has exploded in abundance following the withdrawal of cattle grazing from river banks. C. nudata grows along the edges of the low flow channel, on gravel bars, at the base of cut banks and as islands, its dense root system allowing it to withstand strong flows. C. nudata appears to be altering channel morphology in ways that enhance river complexity, thus enhancing fish habitat and facilitating river restoration goals. The investigators hypothesize that C. nudata facilitates the evolution of compound channels in which C. nudata stabilizes a narrow low flow channel but, unlike many plants, does not slow erosion of the cut banks, such that the bankfull channel continues to move or widen. In some cases, this process is hypothesized to lead to C. nudata patches at the base of banks "detaching" and becoming islands, giving rise to multi-threaded channels. The investigators will use multiple methods to examine these hypotheses. Changes in bank retreat and channel bed erosion/aggradation will be examined using repeated topographic surveys and erosion pins. Bank retreat and island formation will also be examined with aerial imagery. Flow velocity patterns that may explain patterns of erosion/aggradation will be examined with an Acoustic Doppler Current Profiler. With regards to C. nudata distribution, the investigators hypothesize that C. nudata patterns are driven by hydrological variables and sediment type. These hypotheses will be examined with headwaters-to-mouth surveys for C. nudata in three distinct river basins. Until the latter part of the 20th century, river geomorphology focused solely on physical dimensions of river processes. Only recently has vegetation been recognized as having significant effects on river shape and form (Hughes 1997). Nevertheless, current studies of plant-river interactions typically focus on one dimension of this relationship: i.e. either the effects of the river environment on plant communities or the effects of plants on certain physical processes. The proposed research follows Corenblit et al. (2007) who emphasize the reciprocal nature of plant-river relationships and propose the concept of biogeomorphological succession to describe the linked development of river shape and form with riparian plant communities.