Semester of Graduation

Summer 2023

Degree

Master of Science (MS)

Department

The Department of Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Wetlands provide essential ecosystem services and functions, including improving surface water quality through nutrient removal. Louisiana experienced ~4,800 km2 of coastal wetland loss between 1932 and 2016 due to high relative sea level rise and reduced sediment input from the Mississippi River (MR). The 2023 Louisiana Coastal Master Plan aims to restore Louisiana's degraded coastline through restoration projects, including sediment diversions. The Mid-Barataria Sediment Diversion project will reconnect MR sediment-laden water with Barataria Basin degrading marshes. The diversion will also deliver nitrate (NO3-) and soluble reactive phosphorus (SRP) to this basin, potentially negatively impacting water quality.

In Chapter 2, I quantified intact core potential denitrification rates for marsh and submerged sediments from Barataria Basin receiving 0.5 and 2.0 mg NO3-N L−1. In addition, 2 cm of river sediment from an MR crevasse splay was placed over the organic marsh soil to replicate mineral sediment deposition once the MR is reconnected. The post-diversion marsh denitrification rate decreased by ~60% compared to the vegetated marsh rate. However, the estuarine mud and the eroded marsh are always flooded, while the organic marsh is only flooded ~38.5% of the time. Therefore, after diversion, the submerged substrates will perform 3.06x more denitrification than the intertidal organic marsh on the gained land area. These findings can improve the parameterization of water quality models used to predict nutrient loading more accurately across the basin with diversion operation.

In Chapter 3, I examined the temporal P dynamics of the basin, including SRP flux rates and the equilibrium phosphorus concentration (EPC) for four substrates in intact cores receiving one of the four [PO4]3- concentration treatments. Results indicated that all marsh EPCs were below the average MR SRP concentration and were not significantly different, indicating that marsh substrates will absorb SRP during the diversion operation. The estuarine mud EPC was above the MR SRP concentration, indicating that this substrate will release SRP into the water with or without the diversion operation. These findings can inform effective nutrient management strategies for Barataria Basin and other wetland-dominated shorelines.

Date

6-30-2023

Committee Chair

John R. White

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