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Efforts under way to save South Coast salt marsh from 'drowning in place'

A project is under way to save South Coast salt marshes from sea level rise through a relatively new technique called “runneling.”

Runnels are shallow channels dug throughout a marsh to drain pools of water that form as a result of sea level rise, explained Danielle Perry, coastal resilience program director with Mass Audubon, as she stood calf-deep in mud at Allens Pond Wildlife Sanctuary in Dartmouth earlier this spring.

Salt marsh ecosystems are designed to fluctuate between wet and dry. Standing water kills plants, allowing mosquito breeding areas to expand and destroying habitat for endangered birds.

It’s an urgent problem. All over the coast, marshes provide wildlife and fish habitat, filter pollution from entering the watershed, and protect nearby homes from flooding and storm surge.

Plus, salt marshes are able to store more carbon per unit area than forests.

“They're able to store so much carbon because they spend so much time being wet,” Perry said. “And when things are wet, they decompose a lot slower versus in the forest, which has a lot of oxygen. Oxygen is a big part of decomposition and there's so much less oxygen within salt marshes.”

But given the pace of sea level rise, she warned, the marshes are likely to become open water in 50 years if nothing is done.

“So it's really about buying the marsh more time because if we didn't do anything, it would basically be watching the marsh drown in place.”

That’s why scientists and experts with Bristol County Mosquito Control, Mass Audubon, and Save the Bay spent the spring navigating a muddy marsh with high boots and shovels to dig runnels throughout a 25-acre area. The runnels will allow the water to drain from pools in the middle of the marsh into the bay.

“[Runnels] can be up to 12 inches deep. It might be you're only having to dig down three or four inches. But we found that it's better to have them a little wider so they act more like a swale and they don't clog with all this organic material,” said Wenley Ferguson, director of restoration for Save the Bay.

The groups will have to maintain and monitor the runnels’ progress on the marsh in Dartmouth for the next five years before declaring success. The results will be measured by vegetation growth, elevation, and return of endangered birds.

“One of the [goals] of this restoration is trying to allow the high marsh plants to regrow to help preserve that habitat, especially for the salt marsh sparrow,” Perry said.

But so far so good. Some pools were completely drained a week after the team dug the first runnels.

“Runneling is low impact, but high results,” Perry concluded, “which is so nice because often we see all these different restoration initiatives and projects happening and they're so expensive. … All you need for runneling is a shovel and some eager volunteers.”

Mass Audubon’s overall goal is to restore 2,500 acres of coastal habitat by 2026.

Eve Zuckoff covers the environment and human impacts of climate change for CAI.