The Impact of Aquatic Deadzones on Microbial Activity – A Seminar with Dr. Sarah Preheim

—By Emily Myers, PhD of Water IGEP and Department of Human Nutrition, Food, & Exercise, Virginia Tech.

Virginia Tech Life Science Seminar, “Dynamic of Microbial Populations and Biogeochemical Processes in Aquatic Dead-Zones” By Sarah Preheim, Dept of Environmental Health and Engineering, Johns Hopkins University.


Dr. Sarah Preheim recently spoke at the Virginia Tech Life Science Seminar in Fralin Hall. Dr. Preheim comes from the department of Environmental Health and Engineering at Johns Hopkins University. Her seminar on the “Dynamic of Microbial Populations and Biogeochemical Processes in Aquatic Dead-Zones” discussed the biochemical factors that impact the energy that is available to organisms that live in bodies of water.

Oxygen depletion is a major issue impacting water quality in the US and it seems to be worsening with climate change. Microorganisms are a dominant form of biomass on the planet. They’re a significant part of the biosphere. For a frame of reference, Dr. Preheim shared that 1 microliter of sea water has100-1000 bacteria per microliter, so you can imagine the vast scale of bacteria that exist in bodies of water.

Dr. Preheim explained that poor water quality is often related to microbial activity, where too much bacteria in water can use up oxygen and make the water uninhabitable to organisms. These areas become known as aquatic dead zones. These dead zones affect the environment by changing the mobility of water contaminants, impacting nutrient cycling, and producing greenhouse gas emissions. The Chesapeake Bay in Virginia has areas of low oxygen that have experience a loss of habitat for organisms.


The purpose of Dr. Preheim’s research is to develop a mechanistic understanding of microbial community structure and function, predict changes in microbial community structure and function, and understand the role of interactions in microbial functions of interest. Looking at Upper Mystic Lake in Massachusetts, Dr. Preheim and her research team took incremental samples of water from 22 meters below up to surface. These water samples were analyzed for temperature, pH, oxygen, nitrate, iron, sulfate, and characterization of the microbial profile. They found that Upper Mystic Lake is a model system for studying microbial ecosystem with thermal stratification isolating the community from external influence. Using these samples, Dr. Preheim and her team modeled microbial processes, primarily redox reactions, that drive changes in the lake chemistry.

This seminar encouraged me to reflect on the importance of water quality within our ecosystem. Water alone is not enough to sustain life, but rather quality water with the right balance of nutrients is needed. The lack of oxygen in water sources has the potential to damage the life that lives within it. It was fascinating to learn about Dr. Preheim’s research and think about the opportunities for interdisciplinary collaboration with biologists, chemists, and engineers to solve these challenges.

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