Oxbow Persistence as Aquatic Floodplain Habitat: Deciphering the Processes Responsible for the Initial Open-Water Volume Inherited by Oxbow Lakes

牛轭湖是世界上蜿蜒河流沿线分布最广、最独特的地貌之一，是许多濒危物种的重要水生洪泛区栖息地，也是沉积物、营养物质和污染物的重要汇。牛豚在相当长的一段时间内提供这些环境功能的能力取决于它们作为水生栖息地的持久性，这一属性部分取决于它们在形成时继承的初始开放水域体积。继承了大量开放水域的牛豚有大量的储存空间，并可能作为水生栖息地持续几个世纪。相比之下，继承了一小块开放水域的牛轭通常在形成后的几十年内被自然沉积过程完全填满，并转化为陆地栖息地。在气候驱动的环境变化背景下，水生洪泛区栖息地的可持续性取决于一种可靠预测新形成的牛轭在环境中持续时间的方法，这种方法基于对牛轭如何继承其初始开放水域体积的理解。然而，由于缺乏对将分离的河道段转化为牛轭湖的沉积过程的机制分析，这种理解尚未实现。本研究的目的是解释牛轭湖初始开放水域体积的物理机制，这对于解释洪泛平原环境的地貌和生态演变的理论发展至关重要。为了实现这一目的，这项工作将：A.利用实地证据和数值模拟结果，确定新形成的牛轭内沉积速率和沉积模式的主要控制因素；B.利用数值模拟实验，从最近分离的水道段的形式确定建立初始牛轭体积的机制；C.根据沉积学数据和数值模拟记录初始开放水域体积对牛豚作为水生栖息地持久性的影响；D.根据曲流河流的可测量特征，开发并验证一个能够预测牛轭初始开放水域体积的模型。这个项目的结果将首次解释牛弓从河道分离段起源的机械细节。研究结果还将允许开发一个定量模型，能够预测牛轭作为水生栖息地的持久性，从而对《水框架指令》（2000/60/EC）和《栖息地指令》（92/43/EEC）中表达的更广泛的管理需求产生重大影响。

Oxbow lakes are some of the most widespread and distinctive landforms along meandering rivers of the world, functioning as vital aquatic floodplain habitat for many threatened species and as important sinks for sediment, nutrients, and contaminants. The ability of oxbows to provide these environmental functions over a significant duration depends upon their persistence as aquatic habitat, an attribute partly determined by the initial open-water volume they inherit upon their formation. Oxbows that inherit a large open-water volume have substantial storage space and may persist as aquatic habitat for centuries. In contrast, oxbows that inherit a small open-water volume often become completely filled by natural sedimentation processes and converted into terrestrial habitat within decades after their formation. The sustainability of aquatic floodplain habitat in the context of climate-driven environmental change depends upon a means for reliably predicting the duration that newly created oxbows persist in the environment, a means predicated upon an understanding of how oxbows inherit their initial open-water volume. Such an understanding has yet to be achieved, however, due to the absence of a mechanistic analysis of the sedimentation processes responsible for transforming separated segments of river channel into oxbow lakes. The purpose of the proposed research is to explain the physical mechanics that establish the initial open-water volumes of oxbow lakes, critical to the development of theory explaining the geomorphological and ecological evolution of the floodplain environment. To achieve this purpose, the work will: A. Identify the principal controls on rates and patterns of sedimentation within newly forming oxbows using evidence from the field and numerical modelling results; B. Determine the mechanisms that establish the initial oxbow volume from the forms of recently separated channel segments using numerical modelling experiments; C. Document the influence of initial open-water volumes on oxbow persistence as aquatic habitat from sedimentological data and numerical modelling; D. Develop and validate a model capable of predicting the initial open-water volume of oxbows based on measurable characteristics of meandering rivers. The results of this project will, for the first time, explain the mechanistic details of the origin of oxbows from the separated segments of river channels. The results will also allow for the development of a quantitative model capable of predicting oxbow persistence as aquatic habitat and will thus have significant impact on wider management needs expressed in the Water Framework Directive (2000/60/EC) and the Habitats Directive (92/43/EEC).