Semester of Graduation
Summer 2026
Degree Type
Thesis
Degree Name
Masters in Integrative Biology
Department
Department of Ecology, Evolution, and Organismal Biology
Committee Chair/First Advisor
Dr. Troy Mutchler
Second Advisor
Dr. Mark McCarthy
Third Advisor
Dr. Christopher Ward
Abstract
The Maumee River watershed is the largest of any river feeding into the Laurentian Great Lakes and is primarily comprised of agricultural land uses. Most cultivated crops require fertilizer applications to sustain growth and productivity. Fertilizer runoff is a major source of nutrient loading to the river, and total nitrogen (N) and phosphorus (P) inputs contribute to eutrophication and cyanobacterial blooms in the western basin of Lake Erie. This study aimed to characterize Maumee River sediments as net N sinks or sources to the western basin and evaluate N removal efficiency (a valuable ecosystem service) to determine if river sediments alleviate or worsen eutrophication. Water samples and intact sediment cores were collected from four sites along the river and used in a continuous-flow incubation system. Inflow reservoirs were spiked with 15N-labelled ammonium or nitrate, and samples collected during incubations were used to determine net nutrient and dissolved gas (N2 and O2) fluxes. River sediments mostly acted as a net N sink, with higher rates of N removal (e.g., denitrification) than internal N loading (e.g., organic matter remineralization and subsequent bioavailable N release). River sediments were a consistent source of chemically reduced N forms, ammonium and urea, and occasional source of other bioavailable N forms and ortho-phosphate to the river water column. Microbial N removal via denitrification prevents some bioreactive N from reaching western Lake Erie, but consistent sediment ammonium release (accounting for ~59.6% of dissolved N efflux) counteracts this valuable ecosystem service.