Particle Removal and Re-suspension in the near-Field of the Columbia River Plume

在RISE （River Influences on Shelf Ecosystems）项目中，对哥伦比亚河羽流近场的悬浮颗粒浓度和粒径数据与湍流、速度和密度数据进行了同步采集。羽流的这个高能区域的特点是快速混合，初级生产力高，羽流释放大量颗粒，并且根据本提案中描述的工作，从海底重新悬浮和携带颗粒。在本项目中，使用相应的泥沙和湍流数据集来确定在河流羽流中是否观测到粒径与小尺度湍流剪切之间的预测关系。然后将这些结果扩展到确定由锋面过程、底部剪切和内波产生的湍流如何改变羽流不同区域颗粒的保留和去除。提出的工作的第二个目标是调查沉积物再悬浮的过程及其随后进入羽流的夹带。RISE和以前的巡航观测表明，在羽流上升点附近的分层区，大量沉积物在剧烈退潮期间被重新悬浮。这一过程可以解释羽流近场中微量营养素水平相对于海洋和河口增加的现象，并有助于解释羽流系统的高生产力。羽流锋面的通道远低于羽流的底部，将被详细检查，以确定它在重新悬浮和重新夹带沉积物进入羽流中的作用。这项工作正在与RISE项目中对哥伦比亚羽流进行的许多其他物理、生物和地球化学研究同时进行。除了解决与湍流过程在粒子扩散中的作用有关的问题外，拟议的工作将受益于羽流系统的更大的跨学科研究并作出贡献。它将利用已经到位的工作来提供关于沉积物在系统中作用的关键信息，这些信息没有包括在最初的提案中。智力优势：颗粒输运在很大程度上取决于颗粒大小和沉降速度。拟议的工作将测试在一个生产的河流羽流中颗粒大小和湍流之间的关系，并将颗粒场的可变性与羽流过程联系起来。它还将确定垂直（湍流）和水平（平流）粒子通量对羽流的相对贡献。对这些过程的了解将有助于理解河流影响的生态系统、模拟羽流中的沉积物过程的能力，以及从太空感知悬浮沉积物的能力。更广泛的影响：拟议的研究将有助于解释湍流环境中沉积物颗粒的动力学，从而解释污染、病原体或其他颗粒结合物质的运输。高产的哥伦比亚羽也为濒临灭绝的鲑鱼提供栖息地和食物。重悬浮颗粒通过提供微量营养素来提高初级生产力。浑浊为幼鲑提供了免于捕食的机会。该项目将为土木与环境工程专业的研究生艾米丽·斯潘（Emily Spahn）提供支持。除了培训之外，它还将为Spahn女士参加专业会议提供支持。该项目也将为本科生提供支持，从而向学生介绍物理海洋学研究的不同方面。在工程学院多样性和学生服务办公室的帮助下，将努力从代表性不足的群体中招收一名学生。最后，该项目将支持一位早期职业生涯的助理教授。

OCE-0648655During the River Influences on Shelf Ecosystems (RISE) project, suspended particle concentration and size data were collected simultaneously with turbulence, velocity and density data in the near field of the Columbia River plume. This energetic region of the plume is characterized by rapid mixing, high primary productivity, significant release of particles from the plume and, ac-cording to the work described in this proposal, re-suspension and entrainment of particles from the seafloor. In this project, the corresponding sediment and turbulence data sets are used to determine whether predicted relationships between particle size and small-scale turbulent shear are observed in river plumes. These results are then extended to determine how turbulence generated by frontal processes, bottom shear and internal waves modifies the retention and removal of particles in different regions of the plume. A second goal of the proposed work is to investigate the process of sediment re-suspension and its subsequent entrainment into the plume. Observations during RISE and previous cruises suggest that a significant amount of sediment is re-suspended during energetic ebbs in the stratified region offshore of the plume lift-off point. Such processes may explain observations of increased micronutrient levels in the plume near-field relative to the ocean and estuary, and help to explain the high productivity in the plume system. The passage of the plume front, which penetrates well below the base of the plume, will be examined in detail to determine its role in re-suspending and re-entraining sediment into the plume. This work is being done in parallel with many other physical, biological and geochemical studies of the Columbia Plume that are included in the RISE project. In addition to addressing questions relating to the role of turbulent processes on particle dispersal, the proposed work will benefit from and contribute to the larger interdisciplinary study of the plume system. It will leverage work already in place to provide key information about the role of sediment in the system, which was not included in the original proposal. Intellectual merit: Particle transport is determined in large part by particle size via settling velocity. The proposed work will test relationships between particle size and turbulence in a productive river plume and relate variability in the particle field to plume processes. It will also determine the relative contributions to the plume from vertical (turbulent) and horizontal (advective) particle fluxes. Knowledge of these processes will contribute to the understanding of river-influenced ecosystems, the ability to model sediment processes in plumes, and the capability to sense suspended sediment from space.Broader impacts: The proposed research will help explain the dynamics of sediment particles in turbulent environments and thus the transport of pollution, pathogens or other particle-bound matter. The highly productive Columbia Plume also provides habitat and food to endangered salmonids. Resuspended particles enhance primary productivity by supplying micronutrients. Turbidity provides relief from predation for juvenile salmonids. The project will provide support for Emily Spahn, a graduate student in Civil and Environmental Engineering. In addition to training, it will provide support for Ms. Spahn to attend professional conferences. The project will also provide support for an undergraduate student, thus introducing a student to different aspects of physical oceanographic research. Efforts will be made to recruit a student from an underrepresented group with the assistance of the College of Engineering's Diversity and Student Services (DASS) office. Finally, the project will support an early career assistant professor.