Identifier

etd-04082010-094612

Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

A current method to restore Louisiana’s estuaries includes reintroducing freshwater and sediments to wetlands that are hydrologically isolated from the Mississippi River due to the construction of levees. In this dissertation, I examined effects of the second largest freshwater diversion in Louisiana, the Caernarvon Freshwater Diversion (CFD), on estuarine nekton in Breton Sound. Before focusing on Breton Sound, I examined the status of nekton communities in the northern Gulf of Mexico (GOM), and Louisiana wetlands in particular, using the mean trophic level index (MTLI). I demonstrated that commercial targeting caused the previously reported low and declining MTLI from the GOM. Evaluation of Breton Sound alone showed an increasing MTLI, which is possibly a positive effect of hydrological restoration. With a Before-After-Control-Impact study, I demonstrated that nekton species biomass distributions (SBD) changed significantly after the opening of the CFD in 1991. The biomass of selected economically or ecologically important species showed an increase relative to the control (Micropterus salmoides, Micropogonias undulatus, Brevoortia patronus, Farfantepenaeus aztecus and Litopenaeus setiferus), one was not affected (Cynoscion nebulosus). In addition, nekton species richness, abundance and the proportion of smaller individuals increased, indicating increased nursery function. I identified salinity as the main environmental variable separating SBDs among study sites due to freshwater inflow, although seasonal variation had the greatest effect on SBD. The CFD did not change dissolved oxygen or turbidity to the extent that it had an effect on nekton in the areas examined. Applying stable isotope techniques, I identified a positive effect of freshwater inflow on trophic diversity and niche breath of the consumer community, and on the relative contribution of particulate organic matter in the food web, resulting in energy density increases in nekton species. Finally, I created an ecosystem model of Breton Sound, which I used to simulate changes in SBD under different salinity scenarios. This model can be used to evaluate future restoration projects. These various analyses, including the model predictions, revealed only neutral or positive effects of the CFD as currently operated on nekton communities in Breton Sound.

Date

2010

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Cowan, James Howard Jr

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