The Complicated Effect of Phragmites in the Chesapeake Bay

Oct 9, 2019

The phragmites invasion began when it hitched a ride here with European colonists.  Today, the tall reed lines Virginia's waterways, and wetlands, taking over native habitats and clogging waterways throughout the Chesapeake Bay.

But with climate change, the pesky plant is being considered in a different way.

On a visit to the Town of Saxis at the northern tip of the Eastern Shore on the Chesapeake Bay, the first thing to greet you are fields of bobbing, feathery heads of 10-foot phragmites. Underground, roots are spreading throughout the marshes here, taking over wetlands and making the plant hard to eradicate.

M. K. Miles amid phragmites along the edge of the Chesapeake Bay.
Credit Pamela D'Angelo

M. K. Miles grew up on the island before it looked like this. He took me to a friend's yard on the edge of Pocomoke Sound.  "You see this in here. That's their phragmites field," Miles explains. "All they have is this little hole right here that's mowed. The rest of it's all phragmites. So, they're down here for a sea view and they got none. She said 'M.K. what can we do?' I said 'Just cut it.' She said  'You can't just cut marsh grass.'  I said 'it's not marsh grass, it's phragmites.'"

The blocked sea view may be annoying for homeowners, but studies show phragmites can take carbon dioxide out of the air and help stave off sea-level rise by way of those ever-growing roots.

At the Smithsonian's Global Change Research Wetland senior scientist Patrick Megonigal stands next to an ongoing experiment that looks at how excess carbon dioxide affects phragmites.  "The data are telling us that phragmites actually helps the marsh gain elevation faster because of all the root productivity. In that way it might help a marsh faced with very high rates of sea-level rise build upward and remain a marsh instead of becoming open water," Megonigal says.

But for biologists, like Blackwater Wildlife Refuge's Matt Whitbeck, phragmites are a double-edged sword.  "As far as just hanging on to wetland environments, phragmites may not be that bad," Whitbeck admits. "But from a habitat standpoint it's horrible. So, if you're a seaside sparrow, if you're a saltmarsh sparrow, if you're a black rail there's no habitat in a phragmites monoculture for you and that's the issue."

Patrick Megonigal with a phragmites experiment.
Credit Pamela D'Angelo

At the research marsh it's hot and humid. Gary Peresta, an environmental engineer, and Megonigal take me to phragmites experiments where plants are housed in tall PVC pipe frames wrapped in plastic and fed pure carbon dioxide. By the way, Peresta says, there are native phragmites.  "We know from genetics, there's local phragmites that doesn't grow as big," Peresta says. "Same species, it's not even a different species, it's just a different genetic strain. So, we wouldn't even know this before genetics came on."

Peresta also says phragmites are better at building marshes than native species, making it a potential hero as rising seas drown native grasses. That spurs a marsh moment as the two discuss their role in a changing climate. "I think there is a question that the science and management community need to wrestle with which is how much effort do you spend trying to remove it," Patrick Megonigal says. "And this is always a complicated conversation about what the goals are for managing any kind of natural ecosystem like a marsh. Are you trying to manage it for bird habitat, to survive accelerated sea level or for removing nitrogen from the bay? The decisions you make about phragmites, for example, often depend on those goals."

Gary Peresta admits "it's hard for us. We have to be careful as we talk about this stuff because you can't just generalize and say, 'it's all bad,' because it may be better for some species and worse for others. It's just going to change things. That much we can say. Arguably, we are called upon more to be more vocal about what's going on because it is a complicated picture and we need to be honest about the complications but the overall picture is not really in question."

This report, provided by Virginia Public Radio, was made possible with support from the Virginia Education Association.