Date of Award

Winter 2023

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Wilfred Wollheim

Second Advisor

Wilfred Wollheim

Third Advisor

Shan Zuidema

Abstract

Plastic pollution in marine and freshwater ecosystems is a pervasive issue on regional, national, and global scales. A portion of land-based plastics ends up in the world’s oceans through river transport; some land-based plastics are retained within the surface freshwater network. Little is known about how much plastic pollution entering the surface water network is stored vs. exported to oceans. We studied macro- and microplastic in a suburban coastal watershed, the Ipswich River Watershed of Massachusetts, USA in 2022 to gain a better understanding of plastic accumulation in sediments versus downstream flux during baseflow versus storms in streams of different size. We found that macroplastics were higher in the more urbanized headwaters than in the less urbanized river mainstem, with changes along the continuum of river size implying both dilution and the likely retention of macroplastic particles along the stream continuum. Microplastic concentrations stored in sediment were lower in the headwaters than in the river mainstems, implying downstream flux of fine particles. Microplastic fluxes are higher in the mainstem than in the headwaters during typical baseflow conditions, yet are higher in the headwaters during storm events, likely due to stream ‘flashiness’. These findings align with the River Continuum Concept, where coarse materials are retained within river uplands and fine particles are transported downstream. We suggest that the RCC may be a useful paradigm for future plastics research in watersheds where widespread suburban land use dominates.

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