The Opening of the Bonnet Carrẻ In light of record flooding of the Ohio and other tributaries of the Mississippi River, the Army Corps has announced it’s considering opening the Bonnet Carre Spillway to 100,000 cubic feet per second (cfs) or more, around May 9. The River is rising, and so a release now will carry a higher proportion of sediment in the water–if the spillway were a diversion, this would be the time to open it in order to maximize its land-building possibilites. The fresh water and sediment will be a boon to the fresh water wetlands within the spillway over the long term. That much is apparent from the view of the different cypress forests –one starved, and one fed– atop the guide levee. But because we need this fresh water and sediment input, it’s imperative we clean up the river. Flood protection for New Orleans is the priority for opening the Bonnet Carre’, and beneficial use of the spillway is possible, we at GRN are watching to see what effects the degraded waters of the Mississippi will have on Lake Pontchartrain. Spring is when massive amounts of nitrogen and phosphorous pollution flow down the Mississippi to form the Dead Zone offshore. While diverting some of the flow might reduce these pollutants in the Gulf, they could wreak havoc in Lake Pontchartrain by causing harmful algae blooms and a dead zone in the Lake. If the flow ends up at 100,000 cfs, it will be lower than the previous opening in 2008. In that year, the muddy waters of the river moved along the lake’s south shore, and while there were algal blooms, they were not as catastrophic as the blooms from the 1997 release, which caused public health concerns and shaded out Ruppia maritima, one of the Lake’s primary submersed aquatic vegetation (SAV) species. Cladophera growing atop a bed of Ruppia, Goose Point, Lake Pontchartrain, summer 2008 But among the many toxins in the Mississippi is Atrazine, a plant killer which the USGS has begun mapping. And then there are invasive species,, In 2008, the spillway opening released invasive carp into the Bonnet Carre’, and perhaps into a freshened Lake Pontchartrain beyond. Left, a screencap of Hypophthalmichthys molitrix, Silver Carp,in the spillway near the river opening.During this opening of the spillway, could the carp bridge the salt gap of Lake Pontchartrain, and find our Scenic Rivers on the northshore? And if this weren’t enough, there have now been reports of radioactive tritium in the Mississippi, apparently emanating from the Grand Gulf Nuclear Plant in Port Gibson, MS. While we obviously need to do what is necessary to keep folks along the Mississippi safe, we must monitor the potential impacts, and then use this information to help us better live with the river working with upriver states to clean up pollution, and regularly reintroducing the Mississippi into its flood plain and the disappearing wetlands of Louisiana. Scott Eustis is the Coastal Wetland Specialist for GRN.
