Multiscale Experimental and Numerical Investigation of Impacts of Turbulence and Vegetation on Flow and Solute Transport in Hyporheic Zone

潜流带是指溪流、河流和其他水生生态系统中的河床和地表水之间的界面。污染物和营养物质在潜流带的地表和地下水之间不断地交换，控制着水质、底栖微生物的新陈代谢以及相关的生物地球化学循环。在水生生态系统中普遍存在的植被和湍流会影响表层-次表层的交换，从而影响水质和溪流生物地球化学循环。然而，植被和湍流如何影响交换尚不清楚，这使得很难预测河流、湖泊和沿海地区的污染物迁移和生物地球化学循环。这项研究旨在结合水循环水槽中的实验室实验、数值模拟和室外溪流中的现场实验，来量化植被和湍流对浅水区流动和溶质运移的影响。这项研究的结果将有助于改进对河流和其他水生生态系统中污染物迁移和生物地球化学循环的预测，并帮助生态学家设计利用植被来增加沉积物中污染物的保留和降解的溪流恢复项目。拟议的项目还将培训下一代科学家，包括两名研究生和来自代表性不足群体的本科生。此外，还将开展一项示范动手活动，并将其用于为K-12女孩和教师举办的外联活动。这项研究的目的是定量描述湍流和河道内植被对河床交换的作用，并提出一个多尺度的模拟框架，用于预测河床形态、湍流和河道植被曲折河道的河床交换和溶质运移。将在水槽中进行折射率匹配的沉积物和植被的系统控制实验，以及荧光染料成像，以直接可视化和量化湍流和植被引起的潮汐交换。将开发一个基于物理的理论模型来预测作为湍流动能和植被茎大小、体积分数和阻力系数的函数的潜流交换。然后，理论模型将被纳入多尺度数值模拟框架，以研究重要驱动因素(包括近床湍流、植被、河床形态和河道曲折)对复杂曲折河流中水流和溶质运移的综合影响。模拟结果将通过户外曲折河床、湍流和植被的现场示踪实验进一步验证。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Hyporheic zone refers to the interface between the bed and surface water in streams, rivers, and other aquatic ecosystems. Contaminants and nutrients are constantly being exchanged between surface and subsurface water in the hyporheic zone, controlling water quality, the metabolism of benthic microbes, and the associated biogeochemical cycling. Vegetation and turbulence, which are ubiquitous in aquatic ecosystems, affect surface-subsurface exchange and, as such, impact water quality and stream biogeochemical cycling. However, how vegetation and turbulence impact exchange remains unclear, making it difficult to predict contaminant transport and biogeochemical cycling in streams, lakes, and coastal areas. The proposed study aims to combine laboratory experiments in a water-recirculating flume, numerical simulation, and field experiments in an outdoor stream to quantify the impacts of vegetation and turbulence on flow and solute transport in the hyporheic zone. The results from this study will help improve predictions of contaminant transport and biogeochemical cycling in streams and other aquatic ecosystems, as well as help ecologists design stream restoration projects that use vegetation to increase the retention and degradation of contaminants in sediment. The proposed project will also train next-generation scientists, including two graduate students and undergraduates from underrepresented groups. Further, a demonstration hands-on activity will be developed and used in outreach events for K-12 girls and teachers. The goal of the proposed research is to quantitatively characterize the role of turbulence and in-channel vegetation on hyporheic exchange and propose a multi-scale modeling framework for predicting hyporheic exchange and solute transport in meandering channels with bedforms, turbulent flows, and in-channel vegetation. Systematically controlled experiments with refractive index matched sediment and vegetation, as well as fluorescent dye imaging, will be conducted in flumes to directly visualize and quantify the turbulence and vegetation-induced hyporheic exchange. A physics-based theoretical model will be developed to predict hyporheic exchange as a function of turbulent kinetic energy and vegetation stem size, volume fraction, and drag coefficient. The theoretical model will then be incorporated into a multiscale numerical modeling framework to investigate the combined effects of the important drivers (including near-bed turbulence, vegetation, bedforms, and channel meanderings) on flow and solute transport in complex meandering streams. The modeling results will be further validated by field tracer experiments in an outdoor meandering channel with bedforms, turbulent flows, and vegetation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.