Doctoral Dissertation Research: The Role of Large Woody Debris in a Midwestern Low-Energy Stream: Implications for Stream Naturalization

在研究影响河道地貌结构和动态的因素时，人们往往把注意力集中在水和沉积物之间的相互作用上。然而，许多外部因素可以影响这些河流动力学，包括落入河床和沿河床的植物材料。尽管生物群对河流动力学和相关河道形态的影响正受到越来越多的关注，但大多数研究都是在快速流动的河流流经非城市地区的地点进行的。本博士论文研究项目的总体目标是促进对大木质碎屑(LWD)与低坡度曲流河地貌结构和功能之间相互作用的理解。该项目将探索随地分配储存和运输、有机质保留和各种河流过程之间基于过程的相互作用，包括泥沙输送、三维水流结构和沙洲形态发育，并将通过制定一套与现有生物河流过程一致的随地分配管理指南，为河流归化工作提供信息。本项目要研究的具体研究问题包括：(1)在曲流河中随水量的空间分布是如何的？(2)在这种类型的河流系统中，地貌和水文因素是如何影响木质碎屑的动力学的？(3)木质碎屑障碍物如何影响河床物质特征、局部侵蚀和沉积模式、三维水流结构和单个曲流弯尺度上的有机质储量？项目设计和方法将通过研究曲折弯道的三维水流、曲折河流的河床和平面形态发育以及随钻测深对河流生态系统的影响来提供参考。现场数据将在伊利诺伊州东北部凯恩县福克斯河的一条支流杨树溪600米的蜿蜒路段收集。这一研究地点位于一段拉直河段的正上游，该河段是去水道项目的重点，该项目将试图重建一个具有不同河流形态和栖息地的自然功能的曲折系统。实地研究的组成部分包括流域内土地利用变化的特征，利用地理信息系统对研究地点河道位置历史变化的分析，以及对现有历史水文数据的分析。将特别注意以过程为基础的实地调查，重点是在600米范围内随钻测深的动力学和有机质保持，以及随钻测深障碍物与三个曲流弯内地貌过程之间的相互作用。这项研究将有助于全面了解曲流河的地貌动力学，特别是这些系统中生物和非生物成分之间的过程相互作用。这种更好的理解将提供一个更可靠的知识框架，以此为基础制定具有丰富随钻测深的低能量曲折河流的河流归化计划。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

When examining the factors that influence the geomorphic structure and dynamics of stream channels, attention tends to focus on interactions between water and sediments. A number of external factors can influence these fluvial dynamics, however, including plant material that falls into and along stream beds. Although increasing attention is being given to the impact of biota on stream dynamics and related channel morphology, most research has been done in locations where fast-moving streams flow through non-urban areas. The overall goal of this doctoral dissertation research project is to advance the understanding of the interactions between large woody debris (LWD) and the geomorphic structure and function of low-gradient meandering streams. The project will explore process-based interactions between LWD storage and transport, organic matter retention, and a variety of fluvial processes, including sediment transport, three-dimensional flow structure, and bar form development, and it will to inform stream naturalization efforts by developing a set of management guidelines about LWD that are consistent with extant biotic-fluvial processes. Specific research questions to be examined in this project include: (1) How is LWD spatially distributed within a meandering stream?, (2) What geomorphic and hydrologic factors affect the dynamics of woody debris in this type of fluvial system?, and (3) How do woody debris obstructions affect bed material characteristics, local patterns of erosion and deposition, three-dimensional flow structure, and organic matter standing stock at the scale of individual meander bends? The project design and methodologies will be informed by research on three-dimensional flow in meander bends, bedform and planform development in meandering streams, and the influences of LWD on stream ecosystems. Field data are will be collected in a 600-meter meandering section of Poplar Creek, a tributary of the Fox River in Kane County in northeastern Illinois. This study site is located directly upstream of a straightened reach that is the focus of a de-channelization project that will attempt to re-establish a naturally functioning meandering system with diverse in-stream morphology and habitats. Among components of the field study are characterization of land-use change within the watershed, GIS-facilitated analysis of historical changes in channel position at the research site, and analysis of available historical hydrologic data. Special attention will be given to process-based field investigations focusing on LWD dynamics and organic matter retention throughout the 600-meter reach and interactions between LWD obstructions and geomorphological processes within three meander bends. This research project will contribute to the general understanding of the geomorphological dynamics of meandering streams, especially process interactions between biotic and abiotic components of these systems. This improved understanding will provide a more reliable framework of knowledge on which to base stream naturalization plans for low-energy meandering streams with abundant LWD. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.