Asch, RebeccaChan, Christine2025-07-252025-07-252025-052025-05-01May 2025http://hdl.handle.net/10342/14237Microplastics are found in almost all ecosystems on Earth. They pose a threat to organisms through accidental ingestion, bioaccumulation, or by concentrating toxins, such as endocrine disrupters, in the water. While it is understood that rivers transport a great amount of microplastic to the ocean, microplastic movement and settlement in estuaries are not well understood. Increased salinity can increase the benthic accumulation of microplastics due to flocculation, where the ionic activity in the water causes microplastics and suspended material to form dense clumps that settle to the bottom of the water column. We collected surface and benthic samples across a salinity gradient (2-7) during two research cruises at the juncture of the Tar-Pamlico River and Pamlico Sound in April 2024. Our goal was to determine if increased surface salinity led to increased benthic microplastic concentration due to settlement. Microplastics were isolated and counted through a standard operating protocol that included wet peroxide oxidation, density separation, Nile Red dying, fluorescence microscopy, and ImageJ analysis with the MP-VAT2.0 macro. Sampling date and environmental conditions had a greater impact on microplastic concentration compared to salinity. I hypothesize that other factors, such as rainfall, speed of water flow, and proximity to developed areas, may have a greater impact on microplastic presence in the water column vs. the sediment in the Tar-Pamlico River. I found that there is higher plastic in the sediment of the Tar-Pamlico River compared to at the surface of the water column, aligning with other studies of microplastic in estuarine systems. These findings may guide future efforts to better understand microplastic dynamics in the Tar-Pamlico River and Pamlico Sound.application/pdfMicroplasticbenthicsurfaceHonors Thesis2025-06-12