Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

School of Geosciences

Major Professor

Hidetoshi Urakawa, Ph.D.

Co-Major Professor

Mark C. Rains, Ph.D.

Committee Member

Thomas L. Crisman, Ph.D.

Committee Member

Daniel E. Canfield Jr., Ph.D.

Keywords

cyanobacteria, harmful algal blooms, microbiome, water quality

Abstract

For this dissertation I studied the interactions of hydrogen peroxide and cyanobacterial harmful algal blooms (cHABs) dominated by Microcystis in the Caloosahatchee River, FL. Specifically, I examined how taxonomic and functional succession relates to both natural hydrogen peroxide dynamics and hydrogen peroxide added to the environment as a cHAB treatment. Chapter 2 investigated how taxonomic succession and gene expression patterns relate to blooms and associated elevated hydrogen peroxide concentrations. The results showed that gene expressions related to cyanobacterial growth were positively correlated with hydrogen peroxide. The genes identified included enzymes capable of hydrogen peroxide generation which were expressed by blooming Microcystis followed by succeeding cyanobacteria. These results suggest that cyanobacteria are likely responsible for elevated hydrogen peroxide in the aquatic environment. Chapter 3 examined the efficacy and non-target microbial impacts of a low concentration hydrogen peroxide cHAB treatment (490 µM; 16.7 mg/L) in a field application of the Caloosahatchee River. The results indicated this application inhibited the growth of blooming cyanobacteria and ended a bloom through a succession of less affected phytoplankton populations. Chapter 4 investigates the efficacy and non-target microbial impacts of a high-concentration hydrogen peroxide cHAB treatment (14,000 µM; 473 mg/L) in a mesocosm experiment. The results showed this treatment was effective to remove a Microcystis bloom within 24 hours, causing near-total mortality. This came at the cost of non-target impacts to eukaryotic algae and bacteria, the former experiencing similar mortality but the latter recovering by day 2 post-treatment although in a different composition, which retained beneficial microcystin degradation and nutrient cycling functionality. The combined results of this dissertation demonstrated that in the Caloosahatchee River, and likely other aquatic systems worldwide, hydrogen peroxide plays a significant role in both the natural life cycle and human-handed management of cHABs. A thorough understanding of the mechanisms by which cyanobacteria generate hydrogen peroxide and react to hydrogen peroxide added to their environment can enhance effective control of cHABs for more sustainable water management.

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