Drought attacking marsh grass

June 25, 2007

By AMY H. CARTER| The Brunswick News

To see just how ordinary the Golden Isles might look without its "marvelous Marshes of Glynn,"
simply glance to your right the next time you mount the F.J. Torras Causeway bound for St. Simons Island.

Patches of marsh grass on the south side of the causeway are dying, leaving brown sticks and black mud where verdant plains of Spartina alterniflora once swayed.

"I have noticed those myself, and we have gotten just a few reports coast-wide of some new locations of marsh die-back," said Jan Mackinnon, a biologist with the Coastal Resources Division of the Georgia Department of Natural Resources.

Mackinnon is part of a state-wide scientific effort to diagnose the cause of Georgia's marsh loss.
Research led by the Georgia Coastal Research Council has narrowed the cause to lingering drought conditions in Georgia, which were particularly bad during the four years prior to the discovery of the condition in 2001.

The good news is, many of those patches are growing back.

The Jerico site, said to the be the worst of all, "looks fabulous" today, Mackinnon said.

The bad news is, isolated die-offs have continued up and down the coast.

The DNR has received recent reports of dead zones on the Turtle River, off Dover Bluff Creek in Camden County, and in Chatham County.

As part of its ongoing search for a cause, the coastal research council is monitoring the soil chemistry of several sites up and down the coast, looking primarily for levels of naturally occurring metals.

While drought is the leading theory among the various agencies studying the die-back phenomenon, Skidaway's Alexander said human impacts can't be ruled out as culprits.

The die-back "could indicate the level of stress that the system is under already," Alexander said.
"You might be more sensitive to drought stress if you're already under stress from others kinds of conditions."

Altamaha Riverkeeper James Holland, who recently raised questions about a dead zone along the Turtle River near Andrews Island, doesn't buy the drought explanation.

Because of that site's proximity to heavy industry and to recent dredging and spoil disposal work related to deepening the Brunswick Harbor, Holland thinks researchers need to focus more on human impacts.

"This section of marsh appears to be much lower than the rest ... and it's not a small stretch," Holland said.

"I classify it as suspect and it deserves a better look than just a drought. We don't know it's the drought."

Although portions of Georgia's salt marshes have died back and regenerated in the past, Mackinnon said it "certainly hasn't been on the scale that we've seen it (over the last six years)."

That may be due in part to coastal development, she said, which has made the marsh more visible from roadways and subdivisions.

Bad weather impacts marsh
Coastal residents may see even more patches of dead marsh in coming weeks and months as a result of northeasterly winds and storm-driven tides that coincided with the start of the Atlantic Hurricane season June 1.

An unusually thick blanket of marsh wrack, or dead marsh grass, is covering portions of the live marsh, particularly where it meets built-up areas of the coastal plain such as road beds, bulkheads and docks.

"That's a naturally occurring phenomenon," said Jan Mackinnon, a biologist with the Georgia Department of Natural Resources.

Another storm event could remove that wrack quickly, or more slowly if winds and tides don't match the magnitude of recent weeks.

"These dead marsh stems that float up during the spring ... can sit there for months, maybe even years," said Clark Alexander, a professor at the Skidaway Institute of Oceanography near Savannah. "That can kill off the marsh underneath it."

If the wrack is thick enough and remains in place long enough, it suffocates live grasses underneath, resulting in a temporary die-back.

"Because of the importance of wrack to the ecosystem, we certainly don't recommend that people remove it because it's important to the food chain, to life in the marsh," Mackinnon said.

It's been estimated that dead marsh grass is more valuable than live marsh grass to a wider range of species, although Mackinnon said she has not been able to verify that claim.

Marsh wrack is also valuable to the beach ecosystem by helping to build up sand dunes.