Salt marshes play a key role reducing the effects of urbanization and climate change. These marshes absorb carbon dioxide from the atmosphere, and the microbes in the marsh break the carbon down. That’s why researchers, like Northeastern University’s Jennifer Bowen, are working to find out how these vital ecosystems tick.

For over a decade, Bowen and her team have studied the microbes in the sediments of salt marshes in Plum Island Sound, Massachusetts to uncover how the marsh—and the microbes in the marsh—change over time when outside influences, such as nitrogen, are introduced to the system. “A lot of the ecological services that salt marshes provide are facilitated by microbes,” said Bowen. “They are involved in the carbon cycle and the nitrogen cycle, and they remove nutrient pollution through their metabolic process.”

Jennifer Bowen
Prof. Jennifer Bowen

In a new paper published in Nature Communications, Bowen, her graduate student Patrick Kearns, who is the first author on the paper, and researchers from The Marine Biological Laboratory and Woods Hole Oceanographic Institution, set out to discover what would happen to the microbes living in the salt marshes if specific nutrients were added to the environment—essentially emulating possible scenarios associated with urbanization and climate change.

What the team found was by adding nutrients, like nitrogen, there was no change in the types of bacteria present in the salt marsh, but over time, as the conditions changed, a very large proportion of the microbial groups became dormant. “It’s kind of like a bear going into hibernation,” said Bowen. “These dormant bacteria are in a low metabolic state, they just bide their time until environmental conditions return that are suitable for them.” Importantly, when these microbes are dormant they are not contributing to the critical ecosystem services that make salt marshes so important in protecting coastal waters.

“This study shows that human activities are affecting bacteria essential to salt marshes in ways we never suspected,” says Matt Kane, program director in the National Science Foundation (NSF)’s Division of Environmental Biology, which co-funded the research with NSF’s Division of Ocean Sciences.  “Coastal salt marshes provide many benefits – supporting diverse wildlife, helping to reduce pollution, and protecting us from flooding.”  What happens to salt marshes and their bacteria, says Kane, ripples into human lives.

These results help explain why there is so much microbial diversity in salt marshes: One set of microbes are specialized for a specific set of conditions, while another group of bacteria specialize for another set of conditions, and as the environment changes, different bacteria take advantage of conditions that are most suitable to them. Essentially, the salt marsh is in a constant balancing act. “It turns out that we see both an increase in the abundance of bacterial groups that are able to decompose the marsh, and we also see an increase in bacterial groups that can help fix carbon,” said Bowen.

This research, and other projects currently underway in Bowen’s lab, shed more light on how salt marshes are sustained and what could possibly be done to keep them intact. “If a marsh is failing, there is no real way to restore the microbes,” said Bowen. “But what can be created is the environment that will help these microbes thrive.”

Bowen is part of the Urban Coastal Sustainability Initiative in the College of Science at Northeastern University.