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

牛津湖是世界上最广泛和最独特的地貌之一，沿着蜿蜒的河流，是许多受威胁物种的重要水上泛滥平原栖息地，也是沉积物、营养物质和污染物的重要汇。牛弓在相当长的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形成时继承的初始开阔水域体积。继承了大量开阔水域体积的牛弓有相当大的存储空间，可能会作为水生栖息地持续几个世纪。相比之下，继承了较小开阔水域体积的牛弓往往会被自然沉积过程完全填满，并在形成后几十年内转变为陆地栖息地。在气候驱动的环境变化背景下，水生滩涂栖息地的可持续性取决于可靠地预测新形成的牛弓在环境中持续的时间的方法，这一方法是基于对牛弓如何继承其初始开阔水域体积的理解。然而，由于缺乏对将分开的河段转化为牛弓湖的沉积过程的机械分析，这种理解尚未实现。这项拟议研究的目的是解释建立牛弓湖初始开阔水域体积的物理机制，这对解释泛滥平原环境的地貌和生态演变的理论发展至关重要。为实现这一目的，这项工作将：a.利用实地证据和数值模拟结果确定对新形成的牛弓内沉积速率和沉积模式的主要控制因素；b.利用数值模拟实验确定根据最近分离的河道段的形式确定初始牛弓体积的机制；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弓作为水生栖息地的持久性的影响；d.开发和验证一个能够根据曲折河流的可测量特征预测牛弓初始开放水域体积的模型。这个项目的结果将第一次解释从分离的河段中形成牛弓的机制细节。研究结果还将有助于开发能够预测牛弓作为水生生境的持久性的量化模型，因此将对《水框架指令》(2000/60/EC)和《生境指令》(92/43/EEC)所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).