Caernarvon Freshwater Diversion Project

Sunday, March 28, 2004
CC's Journal 13

John Day's white beard glistened in the morning sun, but not as much as the sparkle in his eye when he pulled a core sample out of the Big Mar just below the Caernarvon Freshwater Diversion structure. With a McCauley core tool he had leaned over the edge of a 19-foot Boston whaler and plunged it into the soft bottom of this large square shaped lake. When he pulled it up and opened the metal door of the tool I could see a three-foot long cylinder of mud, or at least that's what I have always called that gooey brown substance. John corrected me. Taking a piece out of the bottom section he rubbed it between his fingers. It was dark brown and black and crumbly like used coffee grounds. "This is peat; dead plant material compacted and aged. In another million years with some more sediment on top this could be oil."

The core sample had four distinct layers. Just above the peat was the exciting part that was twelve inches of grayish clay fine enough to make pottery. This segment John said came from the great flood of 1927 when the Mississippi River levee was dynamited to drain water and save New Orleans. You can read about this event in Rising Tide by John Barry. It took only three months of silt laden Mississippi flood waters to deposit this thick layer. The next and more recent stratum was a gnarl of roots of marsh plants that grew and died from 1928 to 1992, when the Caernarvon diversion structure opened. The top layer was about four inches of new clay sediment combined with roots. This obviously from sediment filled Mississippi River water from the projects flow.

John, a coastal research scientist at LSU, discovered this by accident while working on a 'pulse' study here. He, along with Robert Twilley of University of Louisiana Lafayette, Sea Grant, DNR, Delacroix Corporation and other agencies, is doing research on freshwater flow, sediments and nutrients when the gates are opened to let much needed Mississippi river water into the marshes off the east bank of the Mississippi River near the St. Bernard, Plaquemines Parish line. The pulse means that they use the structure to put a near maximum flow out for a two week period then shut it off for a like period to compare tests.

The Department of Natural Resources describes Caernarvon this way: "The project diverts fresh water and its accompanying nutrients and sediments from the Mississippi River to coastal bays and marshes in Breton Sound for fish and wildlife enhancement. Benefits include restoration of former ecological conditions by controlling salinity and supplementing nutrients and sediments. The bays are important to oyster production and as breeding areas for shrimp and food fishes, while the marsh areas produce food for fur-bearing animals, alligators, and migratory waterfowl. A total of 16,000 acres of marshland will be preserved and 77,000 acres of marshes and bays will be benefited by the project."

Part of John's group endeavor is to study what happens to the nutrients as they leave the Mississippi River and flow over the marshes. Nitrate is one of them and has been in the news each summer for the last ten years; this nutrient is what is thought to be responsible for the dead zone in the coastal Gulf of Mexico each summer. Ammonium and urea that is put on agricultural fields in the Midwest interact with the soil's bacteria that convert those substances into chemical nitrates. Rain runoff makes them flow off the fields and into streams that eventually connect with the Mississippi, which brings them to Louisiana. John tells me that nitrates are chemical ions of NO3 . Bacteria in the marsh take the three oxygen atoms out, and that leaves nitrogen gas, which diffuses into the atmosphere. This chemical reaction takes place as these nitrate-laden waters pass over a radius of about 20 miles of marsh. Studies like this hope to prove the value of getting fresh water, nutrients, and sediment into the marsh. Before its high artificial levee, the Mississippi used to do it naturally and often.

I learned of these ecological processes while I was with John, Robert Twilley, and nine other scientists and grad students in the marsh below Caernarvon. We used bateaus, whalers and airboats to visit their research sites. It is primarily wiregrass marsh here and the fresh green shoots where beautiful against the puffy white clouds coming off the gulf with strong sea breezes. Some areas we traversed had been eaten out by the nutria, which were numerous. I missed a great picture as we were traveling fast in the airboat when startled nutria leaped off his daybed of marsh grass and its first step was on the top of a four-foot alligators head. I think the alligator must have not been hungry for the lucky nutria swam away.

I am beginning to see the differences in the terrain; this looks much different than the marshes of Terrebonne that are dying; and like most of South Louisiana wetlands it is full of life, crabs, snowy egrets, osprey and more. All beautiful to me and my Nikon; necessary to Louisiana's health, recreation and economy.