Title: Anthropogenic Particle (Including Microplastic and Microfiber) Transport and Retention in Streams under Varied Environmental Conditions

Abstract

Microplastics (plastic particles <5 mm) and other anthropogenic particles (i.e., synthetic, semi-synthetic, and anthropogenically modified cellulose particles <5mm) are pollutants of concern in aquatic ecosystems worldwide. Anthropogenic particles enter food chains, adsorb harmful chemical pollutants, and are ubiquitous in aquatic ecosystems. Streams are key sites of anthropogenic particle input, retention, and transport, and empirical measurements of particle movement in lotic ecosystems are needed to inform global budgets of anthropogenic particles and microplastics. However, factors that influence anthropogenic particle retention in lotic ecosystems are poorly understood. This thesis demonstrates how environmental characteristics affect plastic transport and retention in streams in experimental and observational studies.

In our experimental study, we used particle spiraling metrics to directly measure microplastic retention in outdoor, experimental streams at Notre Dame’s Linked Experimental Ecosystem Facility (ND-LEEF). We tested the impact of stream discharge (i.e., high, low), benthic biofilms (i.e., well-established biofilms, reduced biofilms post-scouring), and benthic substrate type (i.e., cobble, pea gravel, sand, mixed substrate) on retention of microplastic fibers using pulsed releases and synchronized water sample collection at three sites downstream. We also collected benthic surface samples for biomass and microplastic density. Samples were filtered directly (water samples) or after peroxide digestion (benthic samples), and experimental microplastic fibers were enumerated visually using a dissecting microscope. Microplastic deposition rates were significantly higher with (1) higher discharge, (2) well established benthic biofilm (as opposed to bare substrate), and (3) larger and more homogeneous substrates.

The observational study examined anthropogenic particles (including microplastics and microfibers) in the Milwaukee River during storm events. Lotic ecosystems are highly variable (e.g., seasonal changes, storm events), and most research assessing anthropogenic particle pollution extrapolates stream particle loads based on measurements during only one point in time. This limits the accuracy of anthropogenic particle and microplastic dynamics models in rivers, where frequent changes in discharge drives retention and transport of fine particles. In this study, we used automated samplers to collect water from the Milwaukee River during four distinct storm events in the spring and summer of 2018. We quantified anthropogenic particle abundance using standard methods and used nearby USGS gauges to determine discharge. Anthropogenic particle concentrations varied significantly among the four sampling periods, highlighting the temporal variability of anthropogenic particle transport across dates. When data from the sampling periods were pooled, there was a decrease in anthropogenic particle concentration in the water column after storm events, indicating that floods may “flush” microplastics from the river. Unexpectedly, anthropogenic particle concentrations were not correlated with other water quality metrics, including concentrations of total suspended solids, fecal coliform, chloride, nitrate, and sulfate, indicating that these metrics cannot be used to estimate microplastic concentrations and likely have distinct driving factors.

These results provide novel insights into the environmental factors controlling anthropogenic particle and microplastic fate and are critical to understanding the role of lotic retention and transport in global plastic budgets.

Acknowledgements

I would like to thank everyone who has made this thesis possible, starting with my advisor, Dr. John Kelly. Dr. Kelly has never once shown any doubt in my abilities to complete this project or make a compelling research story. His support and encouragement made all the difference in bringing this thesis to life, and he has shown me an example of the mentor I hope to be. I would also like to thank Dr. Tim Hoellein, who has been like a second research advisor since the beginning of my time at Loyola. His willingness to help whenever needed and guidance through tough scientific concepts has been crucial to my completion of this thesis. The finished product would not be the same without him. I would also like to thank Dr. Marty Berg for having served on my committee with the kindness of family, despite our lack of a true familial relationship. Also, I would like to thank the collaborators that have helped conduct research for these projects including Dr. Shannon Speir, Dr. Martha Gerig, Deborah Dila, Dr. Ryan Newton, Dr. Sandra McLellan, Dr. Arial Shogren, Dr. Jennifer Tank, and Anna Vincent.

Thanks are also deserving to Loyola University Chicago Department of Biology (especially Audrey Berry, Virginia Lorenzo, and Dr. Terry Grande) for providing funds and support to complete this research. Two years of research assistant awards allowed me to focus deeply on my research. Additionally, thank you to Loyola University Chicago for awarding me travel and research grants, which allowed me to share my research, to meet new colleagues in the field, and to learn material that would further my personal growth as an ecologist. I would also like to thank the Society for Freshwater Science, the Society of Environmental Toxicology and Chemistry Midwestern Chapter, and the Illinois Lakes Management Association for awarding me research and travel grants that helped me complete the research and share results at conferences.

Throughout this process, my friends in the Biology Department, family, and loved ones have all been an extraordinarily helpful safety net and support system. They have provided a hand when sample boxes were too heavy, a walking buddy for writing breaks, and a gentle but firm shove when I felt this thesis was too daunting to start. They have kept my body and mind healthy throughout this experience, and without their help, I truly do not know where I would be. Thank you. 

Vita

Elizabeth “Bizzy” Berg grew up in New Orleans, Louisiana, where she initially developed an interest in science and the environment when volunteering to plant trees in the Jean Lafitte National Historical Park. She received a Bachelor of Science degree in Environmental Science and minored in Sustainability at the University of Notre Dame. During her time there, she worked in a stream biogeochemistry lab, studying agricultural streams and nutrient dynamics, and spent summers at the University of Notre Dame Environmental Research Centers (UNDERC) conducting independent research on the effects of novel stream pollutants, like pharmaceuticals, on stream ecosystem processes. In 2017, Berg joined Dr. John Kelly’s lab at Loyola University Chicago to research the transport of a different novel stream pollutant, microplastics. While at Loyola, Berg has mentored undergraduate and high school students, served as the president of the Biology Graduate Student Association, represented biology students on the Graduate Student Advisory Council, and taught introductory biology labs. Outside of Loyola, she has volunteered with Science Club, an after-school program for Chicago middle schoolers, worked part time for the Aquatic Invasive Species team at Illinois-Indiana Sea Grant, and served on the live auction committee and social media committee for the Society for Freshwater Science.

 

Committee Members:

Dr. John Kelly (advisor)

Dr. Timothy Hoellein

Dr. Martin Berg