Semester of Graduation

Spring 2023

Degree

Master of Oceanography and Coastal Sciences (SOCS)

Department

Department of Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Estuaries within the Gulf of Mexico are exhibiting profound alterations due to climatic changes and the implementation of coastal restoration activities. These changes are attributed to the increasing frequency of harmful cyanobacteria blooms (cyanoHABs) within Lake Pontchartrain, an estuary located in southeastern Louisiana, USA. There is a better understanding into how the opening of the Bonnet Carré Spillway (BCS) impacts cyanoHAB formations compared to the effect of other physical drivers when the spillway doesn’t dominate the system. The goal of this study is to provide a greater understanding of the baseline conditions when the BCS is closed and determine what other physical drivers may promote or demote the formation of cyanoHABs in Lake Pontchartrain Estuary. Field samples were collected during 2021 when the spillway remained closed, and results revealed that there is strong seasonal variation in cyanoHAB formation and that leakage from the spillway and tributary discharge are sufficient to support the development of cyanoHABs in summer. Tides, on the other hand, can serve as a control on cyanobacteria biomass and toxin production. Winds from large scale disturbances like cold fronts and hurricanes resuspend sedimented phosphorus that can support blooms of nitrogen-fixing cyanobacteria, such as Dolichospermum and Cylindrospermum. It is unknown what species of nitrogen-fixing cyanobacteria species, Dolichospermum or Cylindrospermum, can dominate following a physical disturbance. To provide a greater understanding into their cellular response, toxin production, and species selectivity of Dolichospermum and Cylindrospermum, mesocosms were used to model varying levels of shear stress. Results revealed that shear stress, regardless of the levels of 0.1 and 0.4 Pa, limits growth of both species. On the other hand, Cylindrospermum has less of sensitivity to shear stress and is more likely to outcompete Dolichospermum during prolonged physical disturbances. These studies provide a better understanding of the impacts of more natural physical drivers on cyanoHABs formations, species dominance, and toxin production within Lake Pontchartrain Estuary that would ultimately help managers to better plan long-term monitoring of harmful algal blooms.

Date

1-21-2023

Committee Chair

Sibel Bargu

DOI

10.31390/gradschool_theses.5700

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