Covering Louisiana

Jan 12, 2014 12:58 PM by katc

Dying marsh on central Louisiana coast draws scrutiny

It was the mystery of 2000 for coastal researchers. Why were large swaths of coastal marsh turning brown and dying?

It was the talk of coastal meetings, the subject of a number of studies and an additional concern for a coastal landscape that every year experiences large amounts of coastal erosion. The "brown marsh," as it was called, meant that much more acreage was vulnerable to erosion as the plant material that holds the soil together faded away.

Now, researchers are looking toward the causes of another "brown marsh" area, this one primarily in the central coast of Louisiana.

Camille Stagg, ecologist with the U.S. Geological Survey National Wetlands Research Center in Lafayette, said the first major dieback was seen in 2000 during a drought. A smaller dieback was observed in 2009. In September 2012, researchers noticed areas of dieback that upon closer examination look to have occurred in 2011, when there was no drought.

"They seemed to be caused by two different situations," Stagg said about the 2000 and the 2011 marsh diebacks.

Currently, Stagg said, they are examining sites that experienced dieback in 2000 to compare conditions like soil moisture with conditions that existed in 2011, when the latest dieback occurred.

A 2006 report, "The Case of the Dying Marsh Grass," published in response to concern over the scope of the loss and a 2000 executive proclamation from Gov. Mike Foster, found salt marshes in Terrebonne and Lafourche parishes were most impacted, of which 27 percent was severely impacted and 38 percent moderately impacted. The Barataria-Terrebonne National Estuary Program organized the research that became the Brown Marsh Project Team.

According to the report, marsh diebacks aren't uncommon but are usually caused by too much water in an area. That water changes the soil chemistry, causing a die off. The Louisiana brown marsh episode in 2000 was different because the state was in a drought. In addition, previous diebacks of marsh were usually small areas, but again, the episode in 2000 was different.

"In fact, Louisiana's salt marsh dieback in 2000 and 2001 was the largest ever reported in the U.S. Dieback areas averaged about 32 acres and ranged from ¼ acre to about 1,100 acres," the report says.

Researchers concluded the widespread brown marsh episode of 2000 was due to a combination of factors that started with the drought that led to low soil moisture and changes in soil chemistry, among other things.

The dieback wasn't permanent for most of the area, and by 2003, according to the report, only 7 percent of the brown marsh areas showed little or no recovery.

There has been less outcry over the latest brown marsh situation, and estimates have it at about half the size of the 2000 dieback and much more concentrated, primarily in Terrebonne Parish rather than across the coast.

However, the search for answers continues, and Stagg said she hopes to have preliminary findings in time for the State of the Coast conference in March.

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