Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

Excess phosphorus (P) loading is a key driver of eutrophication and harmful algal blooms (HABs) in aquatic systems worldwide. This relationship is of increasing concern in coastal Louisiana, where climate variability, altered hydrology, and land-use change converge, resulting in increased hydrologic and nutrient loading into coastal systems. This dissertation examines controls on P cycling in the Lake Pontchartrain Basin through a multi-scale framework linking estuarine processes, watershed loading, climate and weather patterns, and sediment dynamics. The dissertation begins with an overview of the study region, P dynamics, and changes in hydrology and nutrient loading patterns. Chapter 2 presents a spatial mapping of the distribution and abundance of sediment characteristics and P concentrations across the Lake Pontchartrain Estuary (LPE). Chapter 3 presented a novel approach to determining the equilibrium phosphorus concentration in the water column. This methodology was verified across a range of sediment types and ecosystems. Findings demonstrate that the equilibrium phosphorus concentration (EPCw) of Lake P is 0.025 mg P L-1, lower than previous estimates of 0.70 mg P L-1, further supporting the conclusion that spillway openings have a shorter impact on resulting water quality than initially thought. Chapter 4 investigates internal P loading through diffusion and advection in LPE. These findings demonstrate that advective fluxes increase the short-term availability of SRP and may serve as a mechanistic control on P, releasing buried P and reducing the impact of spillway-induced P loads. Chapter 5 compiles a 25-year record of tributary hydrologic and nutrient loading.  Additionally, this chapter identified the dominant soluble form of riverine P as SRP (~57% of TP), with variation across seasons and storm events. Chapter 6 evaluates the persistence of legacy P in tributary sediments through long-term incubations subjected to dredging and redox treatments. decrease in the SRP release rate under both aerobic and anaerobic water-column treatments. Chapter 7 integrates all this research and offers recommendations for future research to address uncertainties. Across scales, these studies demonstrate how river diversions, weather and climate patterns, watershed development, and sediment legacy nutrients interact to regulate P export to and cycling in Lake Pontchartrain Estuary. This research highlights the importance of comprehensive management strategies that address both external loading and internal sediment sources and account for variable climate conditions.

Date

3-9-2026

Committee Chair

John R White

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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Available for download on Wednesday, July 01, 2026

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