Date of Award:

12-2026

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Committee Chair(s)

Janice Brahney

Committee

Janice Brahney

Committee

Dennis Newell

Committee

Yong Zhou

Abstract

Soils store more carbon than the atmosphere and all plant life combined, so even small changes in how soils cycle carbon can affect the climate. A new pollutant is accumulating in soils around the world: microplastics, tiny fragments of plastic that arrive through farming practices, litter, wastewater, tire wear, and the air. Adding microplastics to soil often increases the carbon dioxide that soil microbes release, so plastic pollution could reduce the carbon that soils store. While this trend is concerning, its cause remains unclear. Microbes may be consuming the plastic itself, or the plastic may prompt them to break down more of the carbon already stored in the soil. In this study, we tested which of these processes is responsible. We mixed new and ultraviolet-aged fragments of high-density polyethylene, a common plastic, into a carbon-rich farm soil from Utah and a carbon-poor savanna soil from South Africa and measured the gas released over 90 days. Because plastic and soil carbon carry different natural chemical signatures, we could tell how much carbon dioxide came from each source. Our results show that microbes do consume the plastic, but extremely slowly: less than one hundredth of one percent was broken down in 90 days, and breakdown slowed sharply after the first weeks. New plastic broke down up to eight times faster than aged plastic, and breakdown was about six times greater in the carbon-poor soil. However, our results also show that plastic can affect the soil’s own carbon. In the carbon-poor soil, a small amount of new plastic nearly doubled the release of carbon already stored there. In total, these results suggest that this plastic will persist in soil for a very long time and that its effect on soil carbon depends on both the soil and how weathered the plastic is. Because most plastic in the environment is weathered, experiments that use new plastic may overestimate how quickly it breaks down and how much carbon dioxide it adds. These findings may be helpful for predicting how accumulating plastic pollution will affect the carbon stored in soils.

Download

Share

COinS

Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .