Sadie Baker

Date Approved


Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department or School


Committee Member

Kristin Judd, PhD

Committee Member

Steven Francoeur, PhD

Committee Member

Paul Price, PhD


Plastics are a global environmental threat due to mass production and the many unknowns regarding the long-term effects of plastic pollution in the environment. Microplastics (MPs) are plastic particles less than 5 mm in size, and they have become ubiquitous in aquatic ecosystems. MPs enter aquatic ecosystems through non-point sources such as urbanization, runoff, or atmospheric fallout or through point-sources such as wastewater treatment plants (WWTPs). To determine MP sources in the Huron River, we evaluated MP load (MPs/day) upstream and downstream from urban centers (Ann Arbor and Ypsilanti) and the Ann Arbor WWTP. The average MP load among sample sites was 7.77 x 106 MPs/day, ranging from 1.47 x 106 to 2.03x 107 MPs/day. Findings indicate that neither urban areas nor the WWTP are significant sources of MP pollution to this section of the Huron River. However, we did find a positive relationship between increased discharge and elevated MP load, suggesting that runoff and rain events might be of greater importance regarding MP pollution. To determine how plastics impact freshwater biofilms, we used EcoPlates to evaluate if plastic surfaces alter biofilm function. High-density polyethylene (HDPE) had the greatest negative impact on metabolic diversity of the biofilms, while polypropylene (PP) had the greatest negative impact on metabolic response. The results of this experiment suggest that plastic substratum have an adverse effect on biofilms overall, but that certain plastic types may have selective impacts on biofilm communities.