Survey reveals problems in local estuaries
Published: Tuesday, September 11, 2012 at 7:29 p.m.
Last Modified: Tuesday, September 11, 2012 at 7:29 p.m.
An aerial survey of the coast after Hurricane Isaac found significant erosion of coastal marshes. But it may have also unveiled another ongoing problem in Terrebonne and Lafourche parishes that dates back further.
Scientists observed significant areas of what's known as “brown marsh” in the Terrebonne and Barataria basins, according to a news release from the U.S. Geological Survey National Wetlands Research Center in Lafayette. Brown marsh is widespread areas of dying marsh, named for the color the grass turns.
The flight last week surveyed areas from the Wax Lake Delta in the Atchaflaya Basin, just west of Terrebonne Parish, to Ship Island, Miss.
“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,” said Phil Turnipseed, National Wetlands Research Center director. “The National Wetlands Research Center is dedicated to continuing to investigate the causes of land loss in order to provide decision makers with information that can help reduce land loss in the future.”
There were previous reports of sudden marsh dieback in the spring and summer of 2012, before Isaac, according to the Geological Survey. That means areas of dieback have been increasing over time and were likely not the result of the storm.
Brown marsh can increase erosion along the coast because if the dieback is extensive enough, wetland plants will lose the root systems that hold land together. As the plants die, the elevation of the marsh sinks when the roots deteriorate, turning marsh to shallow open water.
The first major episode of marsh browning occurred around 2000 when nearly 25,000 acres of Louisiana marsh were affected. Turnipseed said the dieback that year coincided with extreme drought and one of the lowest river levels ever recorded.
Marsh browning began popping up again this summer, and Turnipseed said what's occurring this year is worse than anything seen since 2000. But what's mystifying scientists is that though river levels have been low, this has been a very rainy year in Louisiana.
Scientists want to do more aerial surveys along the coast to continue studying this year's dieback to get to the cause of the phenomenon, he said.
The cause of sudden dieback is still under debate but may be cyclical depending on climate conditions, sea level changes and other environmental factors.
“We've got to get a handle on this because it really exacerbates land loss,” Turnipseed said.
Every acre of marsh counts in Louisiana. Coastal Louisiana has already lost a wetland area the size of Delaware over the last 78 years, a total of about 1,883 square miles, according to a 2011 USGS National Wetlands Research Center study.
Isaac's salty storm surge also appeared to have caused browning and destruction in the marshes east of the Mississippi River.
Damage to wetlands from Isaac's surge was substantial but not unprecedented, the aerial survey found. Damage was recorded across southeast Louisiana but was worst in areas of upper Breton Sound near the hard-hit community of Braithwaite, which experienced extensive flooding. Wetlands in the area had just recently begun to recover from damage incurred during hurricanes Katrina and Gustav, and the storm aggravated those areas.
Significant wetland damage from the storm was also observed on the north shore of Lake Pontchartrain near Slidell, around the Rigolets and the mouth of the Pearl River and on the Chandeleur Islands.
Fewer trees were knocked down by Isaac than past storms. Heavy layers of accumulated organic debris and trash left behind by the surge, known as “wrack fields,” were also seen covering marsh, canals and railroads. In the short term, too much debris can kill wetlands. But eventually debris decomposes and wetlands can come back.
“The before and after images from coastal flyovers reveal some of the Gulf's most biologically and economically significant landscape disappearing before our very eyes, on human time scales,” said U.S. Geological Survey Director Marcia McNutt. “There are many compounding factors that lead to enhanced coastal vulnerability, with hurricanes sweeping in to deliver the coup de grace.”
For more information about Hurricane Isaac's impacts, visit the USGS National Wetlands Research Center's Isaac page at www.nwrc.usgs.gov/hurricane/isaac.
Nikki Buskey can be reached at 857-2205 or email@example.com.
All rights reserved. This copyrighted material may not be re-published without permission. Links are encouraged.