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与沉积物的相互作用上。然而，许多外部因素可以影响这些河流动力学，包括落在河床和河床沿岸的植物物质。虽然人们越来越重视生物群对河流动态和相关河道形态的影响，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低梯度曲流河流地貌结构和功能与大木屑体相互作用的认识。该项目将探索LWD储存和运输、有机物保留和各种河流过程（包括沉积物运输、三维流动结构和沙洲形成）之间基于过程的相互作用，并将通过制定一套与现有生物河流过程一致的LWD管理指南，为溪流自然化工作提供信息。本项目要考察的具体研究问题包括：(1)随钻测井在曲流中的空间分布情况如何？(2)什么样的地貌和水文因素影响了这类河流系统中木质碎屑的动态变化？(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、三维流动结构和单个曲流弯尺度下的有机质存量？项目设计和方法将通过研究曲流弯的三维流动、曲流溪流的河床和平台发育以及随钻测井对溪流生态系统的影响来提供信息。现场数据将在伊利诺伊州东北部凯恩县Fox河的一条支流Poplar Creek的600米蜿蜒路段收集。该研究地点位于一条笔直河段的上游，这是一个去渠化项目的重点，该项目将试图重建一个具有多种河流形态和栖息地的自然功能的曲流系统。实地研究的组成部分包括流域内土地利用变化的特征，利用地理信息系统分析研究地点河道位置的历史变化，以及分析现有的历史水文数据。将特别关注基于过程的现场调查，重点关注整个600米范围内的随钻测井动态和有机质保留率，以及三个曲流弯道内随钻测井障碍物与地貌过程之间的相互作用。该研究项目将有助于对曲流地貌动力学的总体理解，特别是这些系统中生物和非生物组分之间的过程相互作用。这一改进的认识将提供一个更可靠的知识框架，在此基础上制定具有丰富LWD的低能量曲流的溪流归化计划。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.