Wetland damage from Isaac evaluated

Hurricane Isaac and the storm surge it brought to the Louisiana coast tore up marsh grass, contributed to land loss and left behind large “wrack fields” made of torn-up vegetation.

Although post-hurricane damage is expected, Isaac also highlighted areas of the coast that already were under stress from various conditions, including oil spills and marsh die-off, state and federal officials said.

Personnel with the U.S. Geological Survey National Wetlands Research Center in Lafayette, who flew over the coastal areas Sept. 4, found that the hurricane’s effects were greatest in the areas of upper Breton Sound near St. Bernard and upper Plaquemines parishes.

Phil Turnipseed, director of the USGS National Wetlands Research Center, said the flights surveyed coastal areas from Wax Lake Outlet of the Atchafalaya River to Ship Island in Mississippi. The flights were carried out in conjunction with the U.S. Fish and Wildlife Service and the U.S. Department of Agriculture Natural Resources Conservation Service.

The flights found Isaac did substantial damage to coastal wetland areas, but the amount wasn’t unprecedented, compared with other hurricanes that have hit Louisiana.

In addition to the upper Breton Sound area, coastal wetland damage also was seen in areas along the north shore of Lake Pontchartrain near Slidell, around the Rigolets, and locations such as the mouth of the Pearl River and the Chandeleur Islands.

“Previous storms such as hurricanes Audrey, Hilda, Betsy, Andrew, Katrina, Rita, Gustav and Ike are known to have damaged coastal wetlands and contributed to wetland loss, and Isaac appears to have been yet another blow to Louisiana’s fragile but vital coastal wetlands,” according to a news release from the USGS.

“The damage was extensive with Isaac, but we live in hurricane alley,” Turnipseed added.

In some areas, the storm seems to have accelerated problems with “brown marsh” that have been occurring in coastal areas this year for unknown reasons, Turnipseed said. Brown marsh refers to the die-off of marsh grass in large swaths of the coast, a situation that may lead to land loss if the root system can no longer hold onto the soil.

The last major outbreak of brown marsh came in 2000 during a time of drought in the state. There was speculation that it was the drought that led to the escalation of brown marsh conditions. However, this year, there is no drought in the state, so Turnipseed said his and other agencies would be investigating what might be causing it this time.

“This year, we’re seeing a significant dieback before Hurricane Isaac,” Turnipseed said. “It is extensive in Terrebonne and Lafourche parishes.”

Another flight over these areas in Terrebonne and Lafourche parishes was under way Wednesday so experts could get a better estimate of what percentage of the marsh is undergoing this dieback.

“In some areas, it’s hard to tell what was previous brown marsh or what was Hurricane Isaac,” said Gabrielle Bodin, information specialist with the USGS National Wetlands Research Center.

With federal budgets tightening all the time, Turnipseed said, the agencies couldn’t justify doing a flight just to check on the brown marsh syndrome, but Hurricane Isaac provided the justification.

Jerome Zeringue, director of the state’s Coastal Protection and Restoration Authority, said although teams are working on quantifying and evaluating storm damage to coastal areas and ongoing coastal restoration projects, there’s no doubt there’s been damage.

Some investigation has been done, but detailed looks at what damage occurred had to wait until floodwater and storm surge receded from coastal areas. Now that the water has mostly drained away from coastal areas, those assessments are being done now, he said.

The surveys will also cover coastal areas that already were stressed, such as the shorelines that were heavily oiled during the 2010 Deepwater Horizon BP oil leak emergency, he said.

In addition, brown marsh has been seen this summer, some clearly visible on the drive down Lafourche Parish to areas such as Port Fourchon and Grand Isle. Although previous brown marsh incidents were linked with drought, it’s still unknown what is causing the current marsh die-off, he said. One possibility is that it involves the elevation of the marsh itself, but right now, no one really knows, Zeringue said.

“All these things compound the problem and lead to greater loss,” Zeringue said.

Turnipseed agreed.

“Louisiana’s coastal land loss is the greatest environmental, economic and cultural tragedy on the North American Continent, and marsh dieback exacerbates this ongoing disaster,” Turnipseed said.

Hurricane Isaac demonstrated not only how the coast has become more vulnerable to storms, but how that trend could continue without action.

“The problem, obviously, is the storm moved so slow,” Zeringue said.

North of Lake Pontchartrain, not only was storm surge flowing into the lake, but rivers at the same time were flowing south into the lake, carrying large amounts of rainfall from Hurricane Isaac, he said.

“These effects are being felt sooner and farther inland than it used to because we’ve lost that buffer,” he said. As the state continues to lose coastal wetlands, the buffer that could slow down this water is disappearing, he said.

“The more we lose,” Zeringue said, “the more vulnerable we become.”