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

OCE-0648655在河流对陆架生态系统的影响(RISE)项目期间，同时收集了悬浮颗粒浓度和尺寸数据以及哥伦比亚河羽流近场的湍流、速度和密度数据。羽流的这一高能区域的特点是快速混合、高初级生产力、从羽流中大量释放颗粒，以及根据本提案中所述的工作，从海底重新悬浮和夹带颗粒。在这个项目中，相应的泥沙和湍流数据集被用来确定在河流羽流中是否观察到了颗粒尺寸和小尺度湍流切变之间的预测关系。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中颗粒的保留和移除。拟议工作的第二个目标是调查沉积物重新悬浮的过程及其随后进入羽流的过程。在上升和以前巡航期间的观察表明，在羽状物提升点近海的层结区域，有相当数量的沉积物在能量退潮期间被重新悬浮。这样的过程可以解释观察到的烟羽近场中相对于海洋和河口的微量营养素水平的增加，并有助于解释烟羽系统的高生产力。将详细研究羽流锋面穿透到羽流底部以下的通道，以确定其在将沉积物重新悬浮和重新携带到羽流中的作用。这项工作是与RISE项目中包括的许多关于哥伦比亚羽流的其他物理、生物和地球化学研究同步进行的。除了解决与湍流过程对颗粒扩散的作用有关的问题外，拟议的工作还将受益于羽流系统的更大跨学科研究，并对其作出贡献。它将利用已经开展的工作，提供关于沉积物在系统中的作用的关键信息，这一点没有包括在最初的提案中。明智的优点：颗粒的传输在很大程度上取决于颗粒的大小和沉降速度。这项拟议的工作将测试生产性河流羽流中颗粒大小和湍流之间的关系，并将粒子场中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受河流影响的生态系统，对羽流中的沉积物过程进行建模的能力，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沉积物颗粒在湍流环境中的动力学，从而有助于解释污染、病原体或其他颗粒结合物质的传输。高产的哥伦比亚羽流也为濒危的鲑鱼提供了栖息地和食物。再悬浮颗粒通过提供微量营养素来提高初级生产力。浑浊可以减轻幼年鲑鱼捕食的压力。该项目将为土木与环境工程专业的研究生艾米丽·斯潘提供支持。除了培训，它还将为斯潘女士参加专业会议提供支持。该项目还将为本科生提供支持，从而向学生介绍物理海洋研究的不同方面。将努力在工程学院多样性和学生服务办公室的协助下，从代表性不足的群体中招收一名学生。最后，该项目将支持一名早期职业助理教授。

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.