Graduation Year

2026

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Dreux P. Chappell, Ph.D.

Committee Member

Mya Breitbart, Ph.D.

Committee Member

Margaret Brisbin, Ph.D.

Keywords

Tampa Bay, Bioinformatics, Eutrophication, Bacterioplankton, Phytoplankton, Anthropogenic Effects

Abstract

Due to a leak in the lining of a phosphogypsum pond at the former Piney Point phosphate-processing facility in Tampa Bay (Florida, U.S.A.), experienced a large influx of nutrient-dense waters in the early summer of 2021. As an emergency response effort, water samples were collected by researchers at the University of South Florida, College of Marine Science (USF CMS), covering the lower and middle regions of Tampa Bay (TB), over the span of three months (April – June). Illumina amplicon sequencing was performed on DNA from water samples, targeting bacterial and eukaryotic ribosomal rRNA genes, and processed into Amplicon Sequence Variants (ASVs) to investigate the impacts of this discharge on the Bay's microbial plankton community composition. I used statistical methods designed to compensate for the compositional nature of high-throughput amplicon sequencing data to calculate alpha (Shannon, richness, and evenness) and beta (Aitchison distance) diversity metrics. To investigate whether changes in diversity correlate with factors associated with the Piney Point discharges, samples were grouped based on different categorical metadata features, including date and location. Multivariate methods were applied across both categorical and numerical data, including nutrient concentration measurements, to evaluate if there were significant correlations between environmental variables and community composition. The main objective was to investigate the impact nutrient-dense Piney Point discharge waters had on the alpha and beta diversity of the microbial plankton community in adjacent Tampa Bay waters during and over the three months after the discharge event. In turn, this would test the hypothesis that the microbial plankton community composition and diversity of Tampa Bay changed in close spatial and temporal proximity to the discharge site and dissipated with distance and time. Relative abundance data, beta-diversity-based ordinations, and multivariate statistical tests showed that changes in microbial communities were correlated with both changes in nutrient concentration and proximity to Piney Point. These results strongly suggest that the Piney Point discharge influenced the microbial plankton communities in Tampa Bay. Notable results included a higher relative abundance of taxa that can take advantage of large nutrient influxes at stations near the outflow in the period after discharge ended. A caveat of this research is that instrument failures prevented the statistical assessment of temperature and salinity impacts, two other likely drivers of microbial community composition that varied during the time series. Despite this limitation, this research aligns with other studies that have indicated a correlation between the Piney Point discharges and the environmental and economic disruptions experienced around Tampa Bay in 2021.

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