What can save Gulf's fragile coastal wetlands? Salt water, perhaps.
Saltwater marshes on the Gulf Coast are far more resilient than freshwater marshes, new research finds. The results could reframe how scientists work to stop the chronic erosion of coastal wetlands in the Gulf.
Now comes a fresh ingredient for buttressing some of the region's fragile coastal wetlands: Salt water.
That's the bumper-sticker implication of new research looking at the effects of 2005's hurricanes Katrina and Rita on the region's coastal marshes.
The results suggest that salt marshes are far more resilient to the scouring action of storms' waves than their fresh-water counterparts. And they imply that projects to divert Mississippi River water and sediment to rebuild fresh-water marshlands in the delta may be doing more long-term harm than good.
"The introduction of fresh water to marshes as part of restoration efforts may ... weaken existing wetlands, rendering them vulnerable to hurricanes," concludes the team reporting the results in the most recent issue of Proceedings of the National Academy of Sciences.
To counteract that, it may be necessary to allow newly created or augmented freshwater marshes to morph into a saltwater marsh, according to Duncan FitzGerald, a marine geologist at Boston University who has studied the delta region extensively.
"What we want to consider is whether we want those regions that are eventually built to be saltwater communities or freshwater communities," he says.
Dr. FitzGerald and two Boston University colleagues, as well as scientists from the University of New Orleans's Ponchartrain Institute for Environmental Sciences, as well as researchers with the US Army Corps of Engineers comprise the research.
The work touches on an vital issue in the delta region: how best to preserve and enhance wetlands that often are called the region's first line of defense against hurricane storm surges. Specialists trace the gradual disappearance of the Mississippi Delta and its wetlands in no small part to a century of levee-building along the Mississippi to control floods.
Those floods once delivered silt deep into the delta to replace sediment lost to erosion and subsidence. Today, that sediment heads straight into the Gulf of Mexico.
To counteract that, conservation managers have established several diversion projects -- controlled releases of Mississippi River water at strategic points along its route through the delta.
This latest study was triggered by post-Katrina pontoon-plane trips FitzGerald and a colleague took to gather insights on the storm's effect on wetlands.
Flying over a broad expanse of marsh that emptied into Louisiana's Breton Sound, east of the Mississippi's "birds foot" delta, they noticed some striking features.