• The Mississippi: A Visual Biography by Quinta Scott

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Breton Sound and the Oil Slick

Extent of Oil Slick in the Gulf of Mexico, April 29, 2010On April 29. The MODIS image on the Terra satellite captured a wide-view natural-color image of the oil slick (outlined in white) just off the Louisiana coast. The oil slick appears as dull gray interlocking comma shapes, one opaque and the other nearly transparent. Sunglint -- the mirror-like reflection of the sun off the water -- enhances the oil slick’s visibility. The northwestern tip of the oil slick almost touches the Mississippi Delta. Credit: NASA/Earth Observatory/Jesse Allen, using data provided courtesy of the University of Wisconsin’s Space Science and Engineering Center MODIS Direct Broadcast system.

Tentacles of the the Oil Slick reach towards Pass a Loutre WMA at the End of the Bird Foot Delta of the Mississippi River, April 29, 2010. On April 29, the MODIS image on the Terra satellite captured a wide-view natural-color image of the oil slick (outlined in white) just off the Louisiana coast. The oil slick appears as dull gray interlocking comma shapes, one opaque and the other nearly transparent. Sunglint -- the mirror-like reflection of the sun off the water -- enhances the oil slick’s visibility. The northwestern tip of the oil slick almost touches the Mississippi Delta. Credit: NASA/Earth Observatory/Jesse Allen, using data provided courtesy of the University of Wisconsin’s Space Science and Engineering Center MODIS Direct Broadcast system.

The images from NASA show the extent of the Oil Slick as of April 29. The graphic from NOAA show the extent of the Oil Slick between April 25 and April 29, and projects its extent on April 20, when it is expected to creep into the Pass a Loutre WMA, then into Breton Sound, and finally engulf the the Chandeleur Island and the Breton NWR. If it invades Breton Sound, my guess it will also reach into the Delta NWR, which lies between the Mississippi and the Sound.

Graphic from the National Oceanic and Atmospheric Administration, showing the Extent of the Oil Slick between April 25 and April 30, 2010

Beginning in the fall of 2006 and continuing through the fall of 20o7 (really a small amount of time considering the enormity of the issues facing the coastal wetlands) I made five trips to the Louisiana coast, delving deeper and deeper into the deterioration of its wetlands and our attempts to restore them.

At the beginning of last year, when I decided to devote this blog to all things Mississippi River, I decided I would respond to news with history. That is what my book, The Mississippi: A Visual Biography is about, the history of the Mississippi River and the wetlands it created, how they were formed, what we have done to change them, and how we are trying to manage the river and wetlands we have created.

I came away from the experience of photographing, researching, and writing the book as a generalist on the Mississippi and its wetlands, not as an expert on any one portion of the river, but as the rare person who has looked at the river as a whole. The oil leak, such an inadequate description of the rupture of this mile-deep oil well, in the Gulf of Mexico brings home to me the limits of my expertise on the river.

Nevertheless, I shall do what I said I would do: Respond to news with history, this about Breton Sound and oysters:

Breton Sound at the Bohemia State Wildlife Management Area just off Pointe a la Hache

The Mississippi and the Gulf of Mexico performed their annual two-step year after year, exchanging freshwater for salt in the Breton Sound estuary: Saltwater streamed into the basin on gulf tides in the late fall and early winter; during its spring rise the Mississippi flooded the basin with freshwater and sediment and flushed out saltwater. In the 1930s the Corps of Engineers ran their flood protection levees down the west bank of the Mississippi to Bohemia. From then until 1991, when the Louisiana Department on Natural Resources opened the Caernarvon Freshwater Diversion Structure, Breton Sound depended on rainfall for freshwater.

Beginning in 1812 brackish marshes in Breton Sound moved inland, just a little bit between 1812 and 1960. After 1960 the pace of movement sped up. Oil and gas  companies dredged numerous canals that crisscrossed the region, gobbled up 8,256 acres of marsh, extended to the gulf, changed the water flowed through the marshes, and allowed saltwater into fresh and intermediate marshes. Erosion increased to 270 acres a year.

In 1965 Hurricane Betsy washed in saltwater and destroyed the forested wetlands in the backswamp of the Mississippi natural levee close to the head of the sound, turning the area to open water. By 1986 brackish marshes with a salinity of five parts per thousand reached clear north to the Big Mar, an impoundment just off the Mississippi at Caernarvon.

Oysters moved inland with the marshes. By the late 1980s the rising levels of salinity and disease in Breton Sound were killing the oysters. Black drum and conch, saltwater predators, feasted on them. By 1990 saltwater had destroyed 50,000 acres of private oyster beds, which ringed the southern rim of the marshes and followed marshes off the east bank of the Mississippi. Oysters and levels of salinity have been an issue in Breton Sound ever since Slavonian immigrants found an abundance of oysters east of the Mississippi in the 1840s.

Louisianans began discussing the need for freshwater diversions through their levees as early as 1900. They first considered diverting Mississippi water into Breton Sound in 1914 to restore oyster beds. Each flood brought levee breaks that killed the oysters in the first year, but boosted production in the following years. Beginning in 1926 the State tapped the Mississippi with small siphons designed to increase oyster production. In 1955 oysters farmers in Breton Sound requested a freshwater diversion. Four years later the U.S. Fish and Wildlife Service informed the Corps of Engineers that diversions would be advisable. Congress authorized diversions in 1965 and held public hearings in 1968 and 1969, when a diversion at Caernarvon was proposed. For a dozen years the State, the Corps, Fish and Wildlife, and oyster farmers discussed the pros and cons of a diversion. In 1982 the State signed on.

Caernarvon Marshes, Dominated by invasive water hyacinth.

In 1986 Congress authorized a freshwater diversion structure to be built at the Caernarvon crevasse, located just short of the English Turn on the Mississippi fifteen miles south of New Orleans. It was at Caernarvon that the City of New Orleans blasted a crevasse on May 9, 1927 in the levee that released floodwaters from the flooded Mississippi to take pressure off its levees, and save the city from a levee break. The purpose of the new diversion was to reduce salinity in Breton Sound and to increase habitat for fish and wildlife, including nutria and muskrat for the fur trade. Over the years Louisianans put more and more demands on Caernarvon as they learned how to use this new reconstruction tool and recognized its possibilities.

In February 1991 the Corps of Engineers and the Louisiana Department of Natural Resources opened gates in the five fifteen-foot square culverts of the Caernarvon Freshwater Diversion Structure for the first time and released freshwater, sediment, and nutrients into an outfall channel. The Corps designed the structure to flow at the rate of 8,000 cubic feet per second. The intent of the project was to control salinity in Breton Sound, preserve 16,000 acres of marsh, and benefit an additional 77,000 acres of marshes and bays. It must be noted that Congress did not authorize Caernarvon for marsh creation, but rather for salinity reduction. Marsh creation, it seems, was a by-product.

Over the years the DNR changed the operations plan of the diversion structure. At first the agency operated the structure to maintain the salinity of the state oyster seed grounds. For three years in 1994, 1995, and 1996 the DNR kept the gates in the structure wide open during the winter to maximize the amount of sediment pouring into the outfall region and to nourish marsh vegetation. Its third plan provided more consistent patterns of salinity at the five parts per thousand line, which had been pushed south to the northern edge of 1986 oyster leases. The fourth sent high and low pulses of water into the marshes during the spring to mimic actual flooding, to hasten the marshes’ recovery after Katrina and to manage the five parts per thousand salinity line.

By 1998 freshwater marsh plants increased seven-fold in the first seven years. New marshes increased by 406 acres and fresh marsh appeared in the vicinity of Big Mar and around Lake Lery to the east. Salt marsh plants decreased by fifty percent. The basin’s rate of sedimentation kept pace with sea level rise.

As salinity levels dropped, anglers caught twice the largemouth bass. Upward of 25,000 ducks descended on the marsh to winter. Muskrats and alligators built nests, muskrats by the thousands, alligators by the tens. When a red tide threatened Breton Sound in 1996, the Corps of Engineers suspected it was the freshwater diversion that held it back. The new marsh removed nitrogen from the water before it reached the Gulf of Mexico. So did the exploding population of new oysters, which increased from close to zip to thousands. White shrimp increased, but brown shrimp declined, so did the number of blue crabs and red fish. Speckled trout remained about even. All this occurred with no fish kills, no algal blooms, and no decrease in water quality.

When Katrina made landfall at Buras, Louisiana and crossed the Mississippi into Breton Sound, the sound took a big hit.

Katrina’s winds and surging waters ripped across the fresh marshes to the southwest of Caernarvon, sheared them down to the root mat, pushed them up into accordion pleats, and then skidded them across the basin until they hit the elevated ridges–levees, natural levees, and spoil banks–and deposited them there. The winds rolled the marshes into balls, and tossed them into trees or scattered them across shallow ponds–newly created areas of open water.

When Katrina departed Breton Sound, the hurricane left behind forty-one square miles open water, ninety percent of it in fresh and intermediate marshes created by freshwater diversion in the northwestern part of the basin. In some places the water was more than three feet deep. But, for the most part, water skimmed mud flats. It was hoped that the marsh balls, made up of buoyant organic soils, would anchor in the mud flats and reestablish the marsh. Once the Louisiana Department of Natural Resources repaired the diversion structure, the agency opened the gates wide to deliver freshwater and sediment of the most heavily damaged areas.

Mississippi River Ridge at Cane Ridge Slough

In the Spring of 2006 U.S. Geological Survey Landsat maps displayed the areas of open water and new growth in the northwestern portion of Breton Sound. Trees along the Mississippi natural levee were leafing out. So were trees along the Cane Bayou Ridge and the River aux Chenes ridge to the south. Some marshes were recovering between the Caernarvon outfall canal and the north shore of Lake Lery. But the site of the changes in outfall management, the region southwest of Big Mar, looked dead. That all changed by September. The marshes, closest to the outfall management area, those along the Mississippi ridge and those surrounding Lake Lery, were thriving, even though the river was running so low that little water and sediment got to the wetlands. To the south along River aux Chenes and directly west of Bayou Terre aux Boeufs, there was little recovery.Marshes at Delacroix along the Bayou Terre aux Boeufs Ridge

Congress looked at the land loss projections in light of Katrina’s damage to the Caernarvon wetlands and voted to spend $10.1 million dollars to modify the way the Caernarvon project works. Most of the sediment pouring through the gates ended up in Big Mar, not in the wetlands downstream. To deliver more sediment to the marshes, the Corps of Engineers would dredge sediment from the river and run it through a pipeline threaded through the diversion structure to the wetlands. This would add sediment to the region even in years like 2006 when the river ran low. Excavators would deliver dredge through the structure to areas in the wetlands where sediment was most needed. Scientists suggested doing just that at a plan formulation workshop in June 2006. And, they added that the Caernarvon structure could be used to divert freshwater through Bayou la Loutre.[i]

Pelicans await fish diverted from the Mississippi along with freshwater in the Caernarvon Outfall Canal at the head of Breton Sound

Here we are five years later, and it looks like Breton Sound and its oyster beds and fisheries will take another great hit. LaCoastPost has links to articles, which state that Louisiana officials have open the Caernarvon diversion structure and its twin the Davis Pond diversion structure, which diverts freshwater to the Barataria Basin on the west side of the Mississippi, in order to flush freshwater through Breton Sound and the Barataria Basin to counter in influx of oil-laden saltwater into the wetlands.

Update: LaCoastPost has in its May 1st update on the oil slick a map from the New York Times, indicating that the oyster beds in Breton Sound have been closed to harvesting in anticipation that the BP oil slick will foul the beds.

Update: There is a web site refugewatch.org that covers how the U.S. Fish and Wildlife Service is handling the oil that is or may wash into any one of the twenty-five refuges in the five state that line the American shoreline of the Gulf of Mexico. As of May 21, the service is restricting air flights over Breton Island in Breton Sound in order to leave nesting birds in peace.


[i] Day, John W., Jr., et al, “Restoration of the Mississippi Delta: Lessons from Hurricanes Katrina and Rita,” Science,  Vol. 315, March 23, 2007,  1680, http://www.clear.lsu.edu/clear/web-content/Web_items/Science%20Paper.pdf; Barres, John, and James B. Johnston, USGS Reports Latest Land-Water Changes for Southeastn Louisiana,” U.S. Geological Survey, no date, http://www.lca.gov/images/Land%20Water%20Changes%20for%20SE%20LA.pdf; U.S. Geological Survey, “Landsat Thematic Mapper 5 and 7 Satellite After Katrina Images, Caernarvon Area, September 26, 2005, http://www.nwrc.usgs.gov/hurricane/images/katrina/post-katrina-caernarvon-l.jpg; Barras, John, “Caernarvon Diversion Post-Katrina, Illustrating Some Recovery after Spring Flows from the Caernarvon Diversion,” in Lopez, John, “Hurricane Protection: Where Do We Stand?,” Powerpoint to the Tulane Engineering Forum, May 11, 2007, 11, http://tef.tulane.edu/presentations/lopez_john.pdf; Scheifstein, Mark, “Land Lost: Hurricanes Katrina and Rita turned 217 square miles of coastal land and wetlands into water,” New Orleans Time-Picayune, October 11, 2006, http://www.nola.com/recovery/t-p/index.ssf?/recovery/articles/land_lost.html ; U.S. Army Corps of Engineers, New Orleans District, “Louisiana Coastal Protection and Restoration, Enclosure G, Plan Formulation Workshop Report,” June 2006, Prepared by Brett Boston and Vern Herr, Groups Solutions, Inc., G-36, http://lacpr.usace.army.mil/PreliminaryReport%5CEnclosure%20G.pdf.

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3 Responses

  1. Thats a sweet write-up! I am so delighted you chose to publish it.

  2. […] an April 30 post focused on Breton Sound and the Oil Slick she […]

  3. I’m looking forward to getting more information about this topic, don’t worry about negative opinions.

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