Master of Science (MS)
Renewable Natural Resources
The eastern oyster (Crassostrea virginica) and the reefs they create are highly valued for the ecosystem services they provide to coastal estuaries. Recently, their capacity to contribute to nutrient mitigation has spurred interest as researchers have identified 3 mechanisms directly or indirectly associated with oyster reef habitat. This study measured bioassimilation, long-term nutrient burial, and oyster-mediated denitrification in shallow-water (< 1 m water depth) and deep-water (> 1 m water depth) oyster reefs located in two southern Louisiana estuaries. Carbon and nitrogen assimilated into shell and tissue of small (< 75 mm) and large (> 75 mm) oysters was within the range of previous studies but was found to be less influenced by reef type, and more dependent on location specific factors and reproductive status. Post-spawning oysters were found to have higher percent nitrogen content in tissue compared to pre-spawning populations, likely a result of the loss of gametes and increase in feeding related activities during the post-spawn season. Carbon and nitrogen burial rates at oyster reefs ranged from 23.02-57.69 g m-2 yr-1 and 1.09-4.49 g m-2 yr-1 respectively and did not exceed that of other habitat types in Louisiana. However, they were considered to be an important source of nutrient mitigation in these estuaries. Shallow-water reefs buried significantly more nitrogen and carbon, which may be attributed to their proximity to the marsh edge and thus greater influx of detrital material. Closed-system ex-situ incubations revealed some of the highest ever recorded sediment denitrification rates at oyster reefs in the United States (> 1000 µmol m-2 hr-1). However, these values were within the range of those documented in Louisiana coastal systems, and similar to those recorded in nearby reference sediments. Variation in denitrification was found to correspond to site and season, rather than the influence of oyster reef habitat. Because the estuaries in this study are a matrix of reefs and soft bottom sediments, oysters may influence nutrient mitigation outside the boundaries of their active reefs. Thus, bioassimilation, burial, and denitrification may not be localized, but instead may resonate across larger areas as determined by historical reef acreage and hydrodynamics. These are among the first estimates for nutrient mitigation at oyster reefs in Louisiana, and indicate the potential of this ecosystem service in our region. Future research should consider site-specific conditions such as nutrient loading rates, oyster density, and active harvest to accurately quantify this ecosystem service across the coastal region of the state.
Document Availability at the Time of Submission
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Westbrook, Phillip Thomas, "Bioassimilation, Burial, and Sediment Denitrification at Shallow-water and Deep-water Oyster Reefs in Two Louisiana Estuaries" (2016). LSU Master's Theses. 4584.
La Peyre, Megan