Date of Award

Spring 5-3-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Onur Apul

Second Committee Member

Lauren Ross

Third Committee Member

Sean Smith

Abstract

Global plastic production has been increasing over the past 50 years and is causing an increase in plastic waste entering the oceans. Plastic in the ocean is broken down into microplastics by a variety of physical, chemical, and biological processes. This study investigates the extent and potential sources of microplastic fiber pollution in Frenchman Bay, Maine, a coastal bay with complex geomorphology, numerous estuaries and many small tributaries that bring freshwater into it. Frenchman Bay is an important factor in Maine’s economy through its impact on tourism and commercial fishing. It is also a semi-sheltered coastal bay with some freshwater input, which makes it an ideal location to study the land-sea connection of microplastic pollution. Two sampling campaigns were designed for this study and during the first one, 323 fibers were identified from water samples collected on a weekly basis in the Bay from July through October of 2022. The chemical compositions of a subset of these samples were determined by micro-Raman analysis confirming the abundance of microplastic fibers in the Bay. An average of 1.8 fibers/L were found at all sampling locations, suggesting there are an estimated 400 billion microplastic fibers in the top 1 meter of the water column in Frenchman Bay. A complementary sampling campaign was organized to investigate potential land-based sources of microplastic fiber pollution. Grab samples were collected during six sampling events at a variety of rural and urban locations surrounding the Bay. The highest microplastic concentration was from a culvert during a storm event, releasing an average of 15.3 fibers/L directly into Frenchman Bay. Our findings are the first systematic sampling campaign of microplastics in the Bay and can set an example for similar studies in estuary systems that are investigating the land-sea connection of microplastic pollution.

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