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Restoration - Restoration of the Lake Pontchartrain Basin Contributors: Penland, Maygarden, Lake Pontchartrain Basin Foundation This Mississippi River diversion was constructed at Caernarvon in 1991 in order to divert fresh water into the Plaquemines Parish marshes and freshen the water of Breton Sound. It was the first project of its kind and has provided restoration specialists with useful long-term data on its effects on the receiving basin. LDNR is responsible for monitoring the project while the Caernarvon Interagency Advisory Group, consisting of representatives from federal and state agencies, the fishing industry and landowners, provides operational oversight. The outfall management at Caernarvon is a CWPPRA project, but the construction pre-dated implementation of CWPPRA projects.
The project aims to enhance emergent marsh vegetation, reduce marsh loss and increase significant commercial and recreational fisheries and wildlife productivity in the Breton Sound estuary. Benefits include restoration of former ecological conditions by reversing saltwater intrusion and supplementing nutrients and sediment. Prior to the diversion, the area was losing about 1,000 acres annually, but eventually more than 17,000 acres of marshland will be preserved and a further 77,000 acres of marshes and bays will be benefitted by the project.
Rigorous monitoring of the project by the LDNR's Coastal Restoration Division since 1988 has shown that freshwater marsh plants have increased more than seven-fold and brackish marsh plants have increased by almost 50%, while the amount of salt marsh vegetation decreased by more than 50%. Results also show a 17% net increase in marsh acreage within the sampled area. In addition, monitoring shows that oyster production in the public seed grounds in Breton Sound has increased by three orders of magnitude, and the average number of largemouth bass caught has almost doubled. The number of waterfowl using the marsh has increased dramatically since Caernarvon operations began. Similar increases are also noted in the number of alligator and muskrat nests.
This large freshwater diversion project has drawn concern and criticism from several user groups including the shrimp and oyster industry. These users fear the changes on the distribution of their harvest species brought by the diversion. While the white shrimp catch did not significantly change in the post-construction period, the brown shrimp catch in seine and trawls decreased in the post-construction period. Brown shrimp migrate into the estuary in spring, coinciding with diversion operation. The population may be affected by low temperature, turbidity and fresh water. The operation of the diversion has been modified to reduce this negative impact (LDWF). Concerns about the pollution load of Mississippi River water have also generated criticism of Caernarvon. Analysis of monitoring data by Louisiana State University (LSU) scientists has indicated that excess nutrients, especially nitrogen, are removed by the marsh prior to reaching the Gulf of Mexico.
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