Graduation Year

2026

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Mauricio E. Arias, Ph.D.

Committee Member

Katherine Alfredo, Ph.D.

Committee Member

Jeffrey Cunningham, Ph.D.

Committee Member

John Kuhn, Ph.D.

Committee Member

Amy Siuda, Ph.D.

Keywords

Biofouling, Constructed Wetlands, Environmental Models, Plastic Weathering, Raman

Abstract

Microplastics are pervasive in urban aquatic systems, which serve as both conduits of particle flow and incubators of microplastics. These aquatic systems transport microplastic particles while simultaneously altering their physical, chemical, and biological properties. Despite their growing environmental relevance, constructed wetlands and riverine systems remain underrepresented in studies of microplastic fate and transport. This dissertation aims to assess the patterns influencing microplastic transport and aging across urban aquatic environments through a combination of field experiments and mechanistic modeling.

Four interconnected studies were conducted to address this objective. The first investigated the horizontal and vertical transport of microplastics within the Se7en Wetlands, a large surface-flow constructed wetland, revealing that over 93% of microplastics were retained within the first treatment cell due to vegetation entrapment, biofouling, and sedimentation. The second study examined in-situ aging dynamics of microplastics within the wetland, showing substantial microbial colonization but minimal physical or chemical degradation over 18 months, emphasizing microplastic persistence under tertiary treatment conditions. The third study extended this work to a natural riverine system, assessing 24-month aging patterns across five vertical layers of the Hillsborough River. Results demonstrated that polymer chemistry and environmental layer jointly govern early aging: air-exposed particles experienced the highest weathering indices of particle chemical structure, while surface and middle water particles supported extensive microbial colonization. Finally, a multilevel sensitivity analysis of a comprehensive microplastic fate-and-transport model (the “Full Multi” model) identified river depth (totalDepth), particle size (sizeBin), particle shape (shape) and particle density (density) as the dominant parameters controlling vertical transport while reducing model complexity to support management and policy decision-making.

Collectively, these findings reveal that hydromorphological and particle-specific characteristics jointly determine microplastic fate, and that natural and constructed aquatic systems act as both sinks and transformation zones. The work advances the integration of in-situ field data with sensitivity-based modeling approaches, establishing a scalable and decision-relevant framework for microplastic management. This research provides critical insights into the persistence, vertical distribution, and transformation of microplastics in urban waters, supporting improved model design, infrastructure planning, and policy development aimed at mitigating plastic pollution from source to system scale.

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