Collaborative Research: Managing oxygen demand in lakes and reservoirs - a competition between natural and artificial forcing

富营养化分层水体的缺氧是一个全球性的问题，对饮用水处理和冷水渔业产生了负面影响。通过气泡羽流的氧化作用，缓解效果越来越好。虽然气泡羽流可以成功地添加氧气，但添加的能量可能会引起大规模的混合，从而改变储层的热结构，增加沉积物的需氧量，并改变其他沉积物-水的生物地球化学通量（磷、铁、锰、硫化氢和甲烷）。最近对低代谢需氧量的研究表明，氧与曝气湖泊中的气体流速有关，并且由涌流产生的湍流大大增强了沉积物-水界面上的扩散。然而，目前还没有模型可以预测气泡羽流在横流中引起的水流，也没有模型可以将沉积物-水界面的湍流扩散与底栖边界层上方的整体流体速度联系起来。由于需要这两种工具来开发含氧或曝气水库中氧气动力学的综合模型，因此本项目的目的是阐明由自然强迫（例如，流入和沉降）和人工强迫（例如，气泡羽流）产生的流影响湖泊和水库中氧气需求的物理机制。这一目标将通过实验室实验和三个不同水体的实地测量来实现。染料可视化和粒子图像测速技术将用于绘制气泡柱在横流中的侵入动力学。现场实验将使用电导率、温度和深度（CTD）探头和声学多普勒电流剖面仪（ADCP）记录入侵地层和水柱动态；利用声波多普勒测速仪（ADV）和温度和氧气微传感器测量沉积物-水界面的微观结构。pi将与来自西班牙和瑞士的多国跨学科团队合作，并将实现三个主要目标：(1)基于双羽流积分模型方法建立了分层和横流中羽流混合的综合近场模型；(2)采用膜更新理论模型建立了由于水流和湍流混合而通过低流体界面的氧通量模型；(3)将羽流和需氧量模型与三维水动力模型相结合，并使用完整的实验室和现场尺度数据集进行验证。主要的智力价值将是开发第一个科学严谨的变横流气泡羽流模型，包括气泡和水之间的氧气传递，以及基于环境电流和湍流的沉积物-水界面氧气通量的机制模型。作为研究的一个组成部分，野外实验将在三个形态不同的湖泊中进行，提供丰富的数据档案，描述不同气泡羽流的入侵形成、低磷离子的总体需氧量和底栖生物混合。为这三个分量（近场羽流混合、温跃层混合和底栖边界层氧通量）开发的模型弥补了开发一个能够预测湖泊和水库低浓度离子中氧动力学的综合数值湖泊模型所必需的空白。由于美国正在考虑安装价值数百万美元的气泡-羽流扩散器，耦合3D湖泊模型的可用性在设计过程中将是有价值的。拟议活动的主要广泛影响将是完成湖泊数值模型，该模型将能够模拟大范围的湖泊氧气动态。该项目利用了一个跨国、跨学科研究团队的专业知识和资源，这些研究团队在湖泊学、湖泊和水库管理方面处于领先地位。这项研究的结果将通过由联合项目负责人主持的国际水协会湖泊和水库管理专家组，在一个国际论坛上向研究人员和管理人员散发。作为拟议活动的一个组成部分，将制定一项创新计划，指导研究生培养管理大型项目和监督本科生的技能。

AbstractDepletion of oxygen in eutrophic, stratified waterbodies is a significant global problem, which negatively affects drinking-water treatment and cold-water fisheries. Mitigation is increasingly accomplished using oxygenation with bubble plumes. While bubble plumes are successful at adding oxygen, the added energy may induce large-scale mixing, which alters the thermal structure of the reservoir, increases sediment oxygen demand, and changes other sediment-water biogeochemical fluxes (phosphorus, iron, manganese, hydrogen sulfide, and methane). Recent studies of hypolimnetic oxygen demand have shown that oxygen is correlated with the gas flow rate in aerated lakes and that diffusion across the sediment-water interface is greatly enhanced by turbulent episodes generated by seiche currents. Yet, no models exist to predict the currents induced by bubble plumes in crossflow or to relate the turbulent diffusion at the sediment-water interface to the bulk fluid velocity above the benthic boundary layer. Because both of these tools are needed to develop comprehensive models of oxygen dynamics in oxygenated or aerated reservoirs, the purpose of this project is to elucidate the physical mechanisms by which currents resulting from both natural forcing (e.g., inflows and seiches) and artificial forcing (e.g., bubble plumes) affect oxygen demand in lakes and reservoirs. This goal will be realized through laboratory experiments and field measurements in three different waterbodies. Dye visualization and particle image velocimetry will be used to map the intrusion dynamics for bubble plumes in crossflow. Field experiments will document the intrusion formation and water column dynamics using profiles from conductivity, temperature, and depth (CTD) probes and acoustic Doppler current profilers (ADCP); microstructure at the sediment-water interface will be measured using acoustic Doppler velocimetry (ADV) and temperature and oxygen microsensors. The PIs will collaborate with a multinational, interdisciplinary team of colleagues from Spain and Switzerland and will pursue three primary objectives: (1) to develop a comprehensive near-field model for plume mixing in stratification and crossflow based on the double-plume integral model approach, (2) to formulate models for oxygen flux across hypolimnetic interfaces due to currents and turbulent mixing by adapting models from film renewal theory, and (3) to integrate the plume and oxygen demand models with a 3D hydrodynamic model, validated using the complete laboratory and field-scale data sets. The primary intellectual merit will be development of the first scientifically rigorous model for bubble plumes in variable crossflow that includes oxygen transfer between bubbles and water and the formulation of mechanistic models for the flux of oxygen at the sediment-water interface based on ambient currents and turbulence. As an integral part of the research, field experiments will be conducted in three morphologically different lakes, providing a rich archive of data characterizing the intrusion formation from different bubble plumes, the bulk oxygen demand in the hypolimnion, and the benthic mixing. Models developed for these three components (near-field plume mixing, thermocline mixing, and benthic boundary layer oxygen flux) close the gap necessary to develop a comprehensive numerical lake model capable of predicting oxygen dynamics in the hypolimnion of lakes and reservoirs. With several multi-million dollar bubble-plume diffuser installations being considered in the United States, the availability of the coupled 3D lake model will be valuable during design. The primary broader impact of the proposed activities will be the completed numerical lake model, which will be capable of simulating a wide range of lake oxygen dynamics. The project leverages the expertise and resources of a multinational, interdisciplinary team of researchers who are leaders in limnology and lake and reservoir management. The results of this research will be disseminated to researchers and managers in an international forum through the International Water Association Specialist Group on Lake and Reservoir Management chaired by the co-PI. As an integral part of the proposed activities, an innovative program will be developed to mentor graduate students as they develop skills to manage large projects and supervise undergraduates.