Temporal and Hydrologic Factors Influencing Riverine Microplastic Concentrations

Abstract

Microplastic pollution is increasingly studied in freshwater systems due to concerns over the ubiquity of the small plastic particles and their potential effects on aquatic organisms. Still unknown is how in-stream characteristics and temporal variabilities may affect observed riverine microplastic concentrations. In this thesis I investigate dams’ influence on the spatial heterogeneity of microplastics, the affect that time of sampling (time of day and seasonal flow condition) has on the microplastic concentration measured, and whether upstream wastewater management strategies affect the patterns observed. I find that that dams act as a sink for microplastics, capturing significantly higher concentrations of microplastics in the reservoir behind them than is found in areas of settling upstream or downstream of them. My analysis also demonstrates that flow condition is a significant predictor of microplastic concentration at a given location while other measured parameters, including upstream wastewater management strategies, are not. By indicating that flow condition is an important control on measured concentration, this research improves future studies’ ability to interpret and properly apply the findings of existing riverine microplastic surveys. Additionally, by improving our understanding of how hydrologic conditions and the presence of in-stream barriers affect the transport of microplastics in rivers, this research helps to reduce uncertainty in models that attempt to quantify the magnitude of global microplastic pollution and the rate at which it grows.