Date of Award:

5-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Janice Brahney

Committee

Janice Brahney

Committee

Kimberly Hageman

Committee

Erin Rivers

Committee

Kyle Moor

Abstract

Plastic products are produced and discarded at an alarming rate. Bottles, bags, toys, and clothing break down into tiny plastic pieces called microplastics, ranging in size from an eraser on the top of a pencil to smaller in size than a red blood cell. Microplastics are becoming so common in the environment that they travel in the atmosphere, rivers, and ocean currents in ways that are similar to other types of Earth Systems Cycles (i.e., the water cycle). In this study, we explored microplastic sources and sinks in a freshwater river system and how seasonal changes in discharge affect how plastics are transported. For one calendar year, we collected samples from sites influenced by various land uses in the watershed. Microplastics were transported through the system at an average rate of 13,514 ± 32,096 MP·s-1. Microplastic flux (MP · unit of time-1) and concentration (MP · L-1) vary throughout the landscape, highlighting potential sources and sinks. Patterns in microplastic sizes in various reaches of the river identify the potential for multiple sources and help us to infer the influence river features may have on plastic transport. Seasonal patterns in the watershed indicate microplastic flushing from the system during snowmelt season, which is ultimately confirmed by graphing concentration and discharge to explore hysteresis patterns. Microplastic morphology changes throughout the watershed, but harmful particles including fibers and tires are consistently present, posing risk to aquatic species. We discuss how existing sampling methods may be neglecting to capture microplastics in environmental studies. Finally, we observe microplastics in springs in the watershed.

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