Collaborative Research: Role of Interfacial Turbulence in Hyporheic Exchange and Fine Particle Dynamics

为了提高我们评估水生生态系统连通性的能力，评估碳、营养物质和污染物通过河流网络的传播，以及预测人类改变流域的净影响，提高对地表水流动和地下孔隙水之间相互作用的了解是至关重要的。之前由美国国家科学基金会支持的研究发现，水动力相互作用导致河流和底层孔隙水之间的快速交换，以及细颗粒的持续沉积和再悬浮。这些过程预计将极大地影响河网中溶质和颗粒的下游迁移。不幸的是，关于控制这种行为的水动力学机制的信息非常少，因为直接测量孔隙水中的溶质和颗粒动力学一直是极其困难的。本项目的目标是增进对自由流和孔隙水之间的水动力相互作用的基本了解，并利用所获得的信息来改变河流中溶质和颗粒动力学的概念和定量模型。该项目将使用一系列新的流动可视化技术来获得对河流和河床之间的流体交换的直接观测，以及相关的溶质和细悬浮颗粒的通量。结果将被用来确定主要的流体流动过程，负责在多孔环境界面上的溶质和颗粒的传输。这项工作将产生改进的地表-地下流动连续体模型，以及下游溶质和颗粒运移的新概率模型。该项目将通过将项目成果纳入西北大学和伊利诺伊大学的主要外联工作，为更广泛的学生和公众教育做出贡献。重点将帮助K-12学生和邻里社区了解河流过程如何影响水质、人类健康和自然生态系统。PIS还将与几个大学学生团体合作，制定一项新的计划，包括定期在校园内活动，并为在科学领域代表性不足的人群的学生提供指导。总体而言，该项目每年将吸引约1,500名K-12学生和成年公民(在项目的整个生命周期中约4,500人)参与实验室活动和讨论水文过程对可持续发展的重要性。这项工作的主要科学贡献将是改善河流与河床之间水流耦合的基本机制的表征，以及河流中溶解和悬浮物质迁移的新模型。这些模型对于能够预测河流系统可持续管理所需的大规模长期动态是必不可少的。该项目将表征目前从溶质传输模型中缺失的界面通量的重要组成部分，并提供关于细颗粒沉积和再悬浮的关键新观测。需要这些信息来解决淡水系统中的紧迫问题，包括污染物与沉积物的相互作用、保护河流中的生态多样性、河流中的养分保持和碳处理以及通过水传播的疾病。本项目开发的模型可用于评估产生污染物传播和水传播疾病的高风险的因素，从而改善流域管理，将这些风险降至最低。该项目还将通过提高我们预测河流长期生物地球化学和生态动态的能力，促进饮用水资源和水生生态系统的长期可持续性。

It is essential to improve understanding of interactions between surface water flows and underlying porewaters in order to advance our ability to assess connectivity in aquatic ecosystems, evaluate the propagation of carbon, nutrients, and contaminants through river networks, and predict the net effects of human modification of watersheds. Previous NSF-supported research found that hydrodynamic interactions caused rapid exchange between rivers and underlying porewater, along with ongoing deposition and resuspension of fine particles. These processes are expected to substantially influence downstream migration of solutes and particles in river networks. Unfortunately, very little information is available on the hydrodynamic mechanisms that control this behavior because it has been extremely difficult to directly measure solute and particle dynamics in porewaters. The objectives of the current project are to improve fundamental understanding of hydrodynamic interactions between freestream flows and porewaters, and to use the information gained to transform conceptual and quantitative models for solute and particle dynamics in rivers. The project will use an array of new flow visualization technologies to obtain direct observations of fluid exchange between rivers and streambeds, and the associated fluxes of solutes and fine suspended particles. The results will be used to identify the main fluid flow processes responsible for solute and particle transport across porous environmental interfaces. This work will yield improved models for the surface-subsurface flow continuum, as well as new probabilistic models for downstream solute and particle transport. The project will contribute to the broader education of students and the public by incorporating project results into major outreach efforts at Northwestern University and the University of Illinois. Focus will be on helping K-12 students and neighborhood communities to understand how river processes influence water quality, human health, and natural ecosystems. The PIs will also work with several university student groups to develop a new program involving regular on-campus activities and mentoring for students from populations underrepresented in the sciences. Overall, the project will engage ~1,500 K-12 students and adults citizens each year (~4,500 over the lifetime of the project) in laboratory activities and discussions of the significance of hydrological processes to sustainability.The major scientific contributions of this work will be an improved characterization of fundamental mechanisms of flow coupling between rivers and riverbeds, and new models for the migration of dissolved and suspended materials in rivers. Such models are essential to enable the prediction of large-scale, long-term dynamics required for sustainable management of river systems. The project will characterize important components of interfacial flux currently missing from solute transport models, and provide critical new observations of fine particle deposition and resuspension. This information is needed to address pressing problems in freshwater systems, including contaminant interactions with sediments, protection of ecological diversity within rivers, nutrient retention and carbon processing in rivers, and waterborne disease transmission. The models developed in this project can be used to evaluate the factors that produce high risks of transmission of contaminants and waterborne diseases, and thereby improve management of watersheds to minimize these risks. The project will also contribute to longer-term sustainability of drinking water resources and aquatic ecosystems by improving our capability to predict long-term biogeochemical and ecological dynamics in rivers.