Caernarvon diversion

A series of diversion projects have been implemented to reintroduce freshwater and sediment from the Mississippi River into Louisiana coastal wetlands (Figure 18.9). A recent study examined the impact of Mississippi River freshwater diversion on enhancing vertical marsh accretion (mineral and organic matter accumulation) in Breton Sound estuary, a coastal wetland experiencing marsh deterioration as a result of subsidence and saltwater intrusion (DeLaune et al., 2003). The Caernarvon diversion has positively impacted marsh accretion in Brenton Sound estuary helping to slow or reverse wetland loss. Several hundred hectares of new marsh have been created by the introduction of Mississippi River water into the system (Villarrubia, 1998). 

FIGURE 18.9 Location of Caernarvon Diversion and other freshwater sites. 

Sedimentation and vertical marsh accretion, soil mineral and organic matter accumulation, nutrient status, and plant biomass were measured at 20 marsh sites with distance (15-20 km) into estuary at the Caernarvon freshwater diversion (DeLaune et al., 2003). Vertical accretion and... 

This case study demonstrated that freshwater diversion projects such as Caernarvon serve an important role in the reintroduction of freshwater and limited amount of mineral sediment necessary for promoting growth of marsh vegetation (the source of organic matter in marsh soil) in subsiding delta environments. In addition to sediment input, an important influence of the diversion on enhancing marsh stability is associated with the lowering of salinity, which reduces the sediment requirement for marsh maintenance (freshwater marshes have lower mineral sediment requirement than saline marshes). 

Villarrubia, C. R. 1998. Ecosystem response to a freshwater diversion the Caernarvon experience. Abstract. Symposium on recent research in Coastal Louisiana Natural System Function and Response to Human Influences. February 3-5, Lafayette, Louisiana. 

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