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

摘要富营养化分层水体中的氧气耗竭是一个重要的全球性问题，它对饮用水处理和冷水渔业产生了负面影响。越来越多的缓解是通过气泡羽流的充氧实现的。虽然气泡羽流成功地增加了氧气，但增加的能量可能会引起大规模的混合，这改变了水库的热结构，增加了沉积物的需氧量，并改变了其他沉积物-水生物地球化学通量(磷、铁、锰、硫化氢和甲烷)。最近对亚磁需氧量的研究表明，氧气与充气湖泊中的气体流量有关，沉积物-水界面上的扩散因地震流产生的湍流事件而大大增强。然而，目前还没有模型来预测横流中气泡羽流引起的水流，或将沉积物-水界面的湍流扩散与海底边界层上方的整体流体速度联系起来。由于这两种工具都是开发充氧或充气水库中氧气动力学的综合模型所必需的，本项目的目的是阐明自然强迫(如流入和潮汐)和人为强迫(如气泡羽流)产生的水流影响湖泊和水库需氧量的物理机制。这一目标将通过三个不同水体的实验室实验和现场测量来实现。染料可视化和粒子图像测速仪将被用来绘制横流中气泡羽流的入侵动力学图。现场实验将使用电导率、温度和深度(CTD)探头和声学多普勒海流剖面仪(ADCP)的剖面记录入侵形成和水柱动力学；将使用声学多普勒测速仪(ADV)和温度和氧气微型传感器测量沉积物-水界面的微结构。PIS将与来自西班牙和瑞士的多国、跨学科的同事小组合作，并将追求三个主要目标：(1)以双羽流积分模型方法为基础，开发层化和横流中羽流混合的综合近场模型，(2)通过采用膜更新理论的模型，建立由于洋流和湍流混合而穿过亚磁界面的氧通量模型，以及(3)将羽流和需氧量模型与三维流体动力学模型相结合，并使用完整的实验室和野外规模的数据集进行验证。主要的学术价值将是开发出第一个科学上严格的可变横流中气泡羽流模型，其中包括气泡和水之间的氧气转移，以及根据周围水流和湍流建立沉积物-水界面氧通量的机制模型。作为研究的组成部分，现场实验将在三个不同地貌的湖泊中进行，提供丰富的数据档案，描述不同气泡羽流的入侵形成、海底的总体需氧量和海底混合。为这三个组成部分(近场羽流混合、温跃层混合和海底边界层氧通量)开发的模型填补了开发能够预测湖泊和水库地下水位氧气动力学的综合湖泊数值模型所需的空白。随着美国正在考虑安装几个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。拟议活动的主要更广泛影响将是完成的湖泊数值模型，该模型将能够模拟广泛的湖泊氧气动力学。该项目利用了一个跨国、跨学科的研究团队的专业知识和资源，这些研究人员是湖泊学、湖泊和水库管理方面的领导者。这项研究的结果将通过国际水协会湖泊和水库管理专家小组在一个国际论坛上传播给研究人员和管理人员，该专家组由国际水协会共同主持。作为拟议活动的组成部分，将制定一项创新计划，指导研究生发展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.