Honors Theses and Capstones

Date of Award

Spring 2023

Project Type

Senior Honors Thesis

College or School



Earth Sciences

Program or Major

Earth Sciences, Women's and Gender Studies

Degree Name

Bachelor of Arts

First Advisor

Wilfred Wollheim


The importance of plastic pollution research has become apparent as plastic pollution has increased exponentially since its introduction in the 1950s. Plastics mechanically break down into minuscule particles called microplastics, which are plastic particles with a size range of 0.1 micrometers (μm) to 5 millimeters (mm). Most of the research on microplastic pollution has centered around marine ecosystems rather than freshwater ecosystems. More freshwater microplastic research to date is emerging but is still nascent and sparse. Furthermore, the idea that rivers are merely conduits of microplastics to the ocean is even more limited and ignores microplastic loading and retention in rivers. Recent research found that microplastics can be stored in riverine benthic sediments, and consequently, freshwater systems may be considered plastic sinks. Studies also show that high levels of urbanization could be a source of river microplastics. The magnitude of plastic pollution in riverine sediments in relation to the level of urbanization is not yet understood. This project asks the question, “How does plastic stored in stream sediments vary with the intensity of urbanization?” and hypothesizes that plastic storage in stream sediments increases with increasing levels of urbanization because of greater microplastic sources and higher surface runoff to streams. To test this hypothesis, the project measured microplastic storage in the sediments of headwater streams of the Ipswich River watershed in northeastern Massachusetts across a gradient of urban intensity. Urbanization is relatively high in certain reaches of the Ipswich River watershed due to the suburban proximity to Boston, but it also has abundant natural areas. The hypothesis was partially supported, but one forested headwater stream had unexpectedly high microplastic concentration. The study results inform the strength of influence urban inputs have on benthic plastic storage in headwaters.