Semester of Graduation

May 2024

Degree

Master of Oceanography and Coastal Sciences (SOCS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Marsh edge erosion caused by wave impact is a major mechanism of marsh loss in coastal Louisiana. Marsh edge erodibility, the rate of marsh edge retreat per unit wave power, is highly heterogeneous. To understand how marsh soil and vegetation properties relate to this variability, a basin-wide survey was conducted across different salinities in Barataria Basin. At all sites, marsh soils are strongest within the top 20 cm (the rhizosphere). Variability among marsh types is largest at the marsh edge, where saline marshes are stronger than brackish, intermediate, and fresh marshes. Marsh edge rhizosphere strength generally decreases with decreasing marsh surface elevation, despite a high degree of variability (scatter) observed within the dataset. Marsh edge erodibility is inversely correlated to rhizosphere shear strength, especially in saline marshes. Marsh edge erodibility is anomalously high within intermediate marshes adjacent to the Gulf Intracoastal Waterway (GIWW), a source of nutrients into the basin. This may indicate that nutrients could reduce marsh strength in intermediate marshes, increasing erodibility. Further, low rhizosphere strength in fresh marshes associated with vegetation mortality due to fire and a consequent recovery is detected. Blocks of marsh abducted during Hurricane Ida and subsequently redeposited displayed similar properties to the marsh type they are suspected to have originated from. Overall, this study indicates low-salinity, low-elevation marshes are particularly weak and vulnerable to wave-induced edge erosion. These findings provide an increased understanding of the relationship between marsh soil properties to erosion susceptibility and can be used to improve coastal morphodynamic models within Barataria Basin. Lastly, the adoption of marsh soil shear strength testing into existing vegetation, elevation, and soil monitoring programs may provide a more comprehensive understanding of marsh health through space and time.

Date

4-2-2024

Committee Chair

Mariotti, Giulio

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Available for download on Friday, April 02, 2027

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