Researchers To Study Salt Marshes As Carbon Exporters

by Alan Pollock
Salt marshes, like the massive one at Chatham’s Strong Island, are natural carbon sinks. FILE PHOTO Salt marshes, like the massive one at Chatham’s Strong Island, are natural carbon sinks. FILE PHOTO

CHATHAM – A group of academic researchers and government scientists has asked to install monitoring equipment in the marsh behind Harding’s Beach and near Cockle Cove to better understand how marshes export dissolved carbon to the coastal waters. Because this so-called “blue carbon” can be stored in the oceans for thousands of years, it plays a role in mitigating climate change.

Funded by a grant from the National Science Foundation, the two-year study is being conducted by Joseph Tamborski of Old Dominion University, the U.S. Geological Survey’s Woods Hole Coastal and Marine Science Center and Woods Hole Oceanographic Institution. Researchers will deploy equipment to take measurements in the marsh behind Harding’s Beach next summer and will move the equipment to Cockle Cove Creek in the summer of 2025.

On behalf of the researchers, Natural Resources Director Greg Berman asked the select board for permission for the installations late last month.

“Part of this is to request permission. The other part is to notify yourselves and the town that nobody’s constructing a cell phone tower, and a UFO hasn’t landed,” he said. Each site will host a tripod-mounted weather station that stands about six feet high, as well as aluminum collars mounted near the surface of the marsh to measure gas flux. Other equipment will be submerged in the tidal creeks. “All of the equipment is taken away at the end of the season,” Berman said.

It’s well known that the sediment in salt marshes stores atmospheric carbon, but the study aims to better understand what happens when that carbon is released over time. Essentially, the study will determine how much of the carbon is released to the atmosphere and how much is washed away into the ocean.

“The breakdown of marshes can lead to increased carbon dioxide in the atmosphere, which drives climate change, global warming, sea level rise,” Berman said. “These scientists would like to explore the potential for the carbon within the pore space of the soil of the marsh being taken offshore and into the ocean.” They hypothesize that marsh platforms with lower elevations export a greater portion to the ocean.

“Importantly, this ‘blue carbon’ can be stored in the oceans for thousands of years, making it a long-term sink of atmospheric CO₂,” Tamborski wrote in a letter to the town.

“Part of the reason why they’re looking in this area is because our salt marshes really capture more, and store more, carbon than our land-based forests,” Berman said. “So as they degrade, they want to get a better feel for how this region might impact the global carbon cycle.”

Around the world, salt marshes are being degraded by rising sea levels, which can cause changes in the natural vegetation and a release of stored carbon.

The equipment will measure the alkalinity and dissolved carbon in the marsh system’s “pore water.” While this water can tend to increase the acidity of ocean water — a major environmental concern — exporting carbon this way contributes less to climate change than atmospheric carbon does.

“Ocean acidification is a growing concern for a lot of people. I’ve seen some of the studies that we were part of with our fish weirs,” said select board member Shareen Davis, whose family fishes commercially. “I’m really happy to see this kind of work being done in the town.”

While the Chatham study is focused on two sites, the research is part of a larger study of marshes around New England.

“The study of looking at salt marsh pore water being a carbon export offshore, the blue carbon idea, is international,” Berman said.

“We have a wonderful natural environment here, and we’ve talked about inviting academic institutions into town to do this kind of study,” Davis said. “This is spot-on what we’d like to see. So I’m very supportive of this.”

“I think it’s exciting and I wish them well,” board member Jeffrey Dykens added. “We’re a perfect Petri dish for this kind of stuff.”

“We have planned to have them get in touch with the energy and climate action committee because there is a salt marsh study that’s getting very close to realization,” Berman noted. “I think there might be a nice symmetry between the two.”

The installation of equipment in the marsh at Harding’s Beach is expected to take place in April.