Collaborative Research: Investigating Hyporheic Zone Reaction Enhancement by Bioclogging Across Scales

河床会向大气中排放一种强有力的温室气体--一氧化二氮，这种气体会阻挡向外辐射的太阳辐射，导致气候变暖。由于缺乏对有利于其生产的条件的了解，从河流中排放的一氧化二氮的数量很难估计。一氧化二氮是在没有氧气的大量但较小的区域产生的。然而，这些“微区”的大小使它们极难定位和测量。该项目将研究在模拟河流沉积物的受控条件下形成低氧微区的情况。实验和数值模拟将被用来确定在沉积物中生长的细菌如何调节这些微区的形成。了解细菌如何控制低氧微区的大小、位置和持续时间，将提供更确定地估计河流一氧化二氮排放所需的关键信息。这项研究不仅将揭示导致河床一氧化二氮排放的过程，并为减少温室气体排放的战略设计提供信息，而且还将增进对低氧微型区域如何调节地下水中污染物转化和养分循环的理解。研究团队将通过指导博士后、研究生和本科生等不同背景的学员来培养未来的环境工程师。此外，该小组将领导一些活动，以加强公众对浅层地下水如何影响河流水质的了解，包括地下水基础STEM暑期计划，以及在河流修复地点为K-12学生和公众进行的实地演示。该项目的目标是确定一氧化二氮的产生如何与河流沉积物中缺氧微区的形成动态相联系。项目组将进行沉淀柱实验，以量化宏观尺度上的一氧化二氮产量，进行微流体实验，以表征孔隙尺度上缺氧微区的空间和时间分布，并使用基于过程的数值模拟将两个尺度联系起来。通过这些努力，研究人员将检验这一新的假设，即流体流动和微生物生物膜生长之间的耦合决定了缺氧微区的时空动力学，以及微区内促进一氧化二氮产生的反应物的输送。研究成果将提供对微尺度过程和生物活动如何影响多孔介质中的大尺度行为的基本理解，以及对溶质传输、污染物命运和温室气体通量的影响。该奖项反映了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。

Riverbeds can emit a potent greenhouse gas, nitrous oxide, to the atmosphere, which traps outgoing solar radiation and leads to climate warming. The amount of nitrous oxide emitted from rivers is difficult to estimate due to a lack of knowledge of the conditions that favor its production. Nitrous oxide is produced in abundant but small zones where oxygen is not available. However, the size of these “microzones” makes them extremely difficult to locate and measure. This project will investigate the formation of low oxygen microzones in controlled conditions that mimic river sediments. Experiments and numerical simulations will be used to determine how bacteria growing in the sediments regulate the formation of these microzones. Knowledge of how bacteria control the size, location, and duration of low oxygen microzones will provide key information needed to estimate river nitrous oxide emissions with greater certainty. This research will not only reveal the processes responsible for nitrous oxide emissions from riverbeds and inform the design of strategies that can reduce greenhouse gas emissions, but it will also improve understanding of how low oxygen microzones regulate contaminant transformation and nutrient cycling in groundwater. The research team will train future environmental engineers by mentoring trainees from diverse backgrounds at the postdoctoral, graduate, and undergraduate levels. Further, the team will lead activities to enhance public understanding of how shallow groundwater influences water quality in rivers, including a Groundwater Basics STEM summer program and field demonstrations for K-12 students and the public at a river restoration site.The goal of this project is to determine how nitrous oxide production is linked to the dynamics of anoxic microzone formation in river sediments. The project team will perform sediment column experiments to quantify nitrous oxide production at the macroscale, perform microfluidic experiments to characterize the spatial and temporal occurrence of anoxic microzones at the pore scale, and use process-based numerical simulations to link the two scales. Through these efforts, the researchers will test the novel hypothesis that coupling between fluid flow and microbial biofilm growth determines the spatio-temporal dynamics of anoxic microzones, as well as the delivery of reactants that fuel the production of nitrous oxide within microzones. Research outcomes will provide a fundamental understanding of how microscale processes and biological activity influence macroscale behavior in porous media, with implications for solute transport, contaminant fate, and greenhouse gas fluxes.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.