Bubble-mediated transport and aerosolization of microorganisms: implications for natural and manual aeration to adjacent communities

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Aeration (the introduction of air bubbles into water) either through mechanical systems or through wind/wave action represents a common way for oxygen to become dissolved into water bodies. Such processes are important to prevent the formation of “dead-zones”, areas where the oxygen concentration is too low to support animal life. Because bubbles are lighter than water, they naturally rise to the surface. Small particles like sediment, microbes, toxins, and organic matter, as well as gases can be swept along with the bubble as it travels to the surface. When the bubble bursts at the surface, bacteria and other particles and gases can disperse through the air, increasing the chances of human exposure. While we understand the power of bubbles to aerosolize particles into the air, the underlying causes are poorly understood. The goal of this project is to understand how environmental conditions such as bubble size, microbial cell size, and water chemistry affects microbial transport and aerosol generation. This goal will be achieved using both controlled laboratory experiments and field study at Rock Creek (Pasadena, MD, USA), a low oxygen water body that has a mechanical aeration system to prevent dead zone formation. This research is based on the hypothesis that changes in bubble and microbial cell size, as well as water chemistry parameters can be used to predict microbial aerosolization. The public will be engaged in this research through citizen science projects, increasing the scientific literacy of the Nation. Successful completion of this research has potential to protect human and ecological health through prevention and control of pathogens and toxin aerosolization. Microorganisms live in an environment filled with air-water interfaces, such as those found at the surface of a lake, around gas bubbles from aeration, or in water pockets trapped in soils. The behavior of microorganisms at these multiphase interfaces is largely understudied, in spite of their importance in controlling air-water-soil mass transfer. The goal of this research is to address these gaps in knowledge to understand how bubble size, microbial cell size, and water salinity affects bubble-mediated microbial transport and aerosolization. The research is guided by the hypothesis that changes in environmental variables (bubble size, microbe size, salinity) will result in differences in transport and aerosolization that can be predicted from equations and relationship previously derived for model colloids. These predictions will be tested across multiple scales using diverse microorganisms ranging in size from viruses to eukaryotic algae under controlled laboratory conditions to measure interfacial and small-scale transport. Field-scale transport will be measured during mechanical aeration of a low-oxygen aquatic environment (Rock Creek, Pasadena, MD). Interactions and bubble-mediated transport and aerosolization will be quantified with state-of-the-art particle tracking methods, flow cytometry, quantitative polymerase chain reaction, and microbial community characterization. A diverse group of high school, undergraduate, and graduate students will be trained in inter-disciplinary research topics and the public will be engaged in the research through a number of outreach activities. These experiments will result in quantifiable relationships that can be used to understand how bubble-generating processes will impact microbial dispersal within the water column and into aerosols, which can be applied to microbial ecology or microbial risk assessment for novel or worsening microbial threats.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.