Date of this Version
Hansen, S. P. (2019). Predictive Modeling of Fate and Transport of Three Prevalent Contaminants in Midwest Agroecosystem Surface Waters: Nitrate-N, Atrazine, and Escherichia coli (master's thesis). University of Nebraska - Lincoln, Lincoln, United States
The majority of streams and rivers in the United States (U.S.) are ecologically impaired, or threatened by anthropogenic stressors. Recent reports have found atrazine in drinking water to be associated with increased birth defects and incidences of Non-Hodgkin’s Lymphoma, with higher levels of significance from exposure to both atrazine and nitrate-N. In contrast, recent illnesses from E. coli contaminating vegetables that originated from irrigation water has increased awareness of identifying sources of E. coli entering irrigation reservoirs.
Methods to accurately predict atrazine and E. coli occurrence and potential sources in waterways continue to limit the identifying appropriate and effective prevention and treatment practices. Therefore, the primary objectives of this study were to: 1) Identify watersheds across Nebraska that were at risk for exceeding nitrate-N and atrazine maximum contaminant limits (MCLs) in surface water, 2) Determine the specific times of greatest risk for exposure to atrazine throughout the year, 3) Determine the load of E. coli during storm events in a hydrologic controlled stream situated adjacent to a livestock grazing operations and centered in the fly zone for avian migration in the Midwest, and 4) Identify trends between E. coli concentrations, grazing rotations, and avian migrations patterns.
Findings from objectives 1 and 2 of this project identified impairments for both nitrate-N and atrazine in the surface water during the early growing season in the southeastern region of Nebraska. Objectives 3 and 4 required a complex combination of bovine density and waterfowl migration patterns to evaluate the impact of E. coli concentrations in stream water, with the downstream reservoir had exceedance probabilities above the EPA freshwater criteria >85% of the growing season following rainfall events. Further, methodology developed in this project has the potential for application in regions with higher dependency on surface water to determine agrochemical and E. coli load influxes from upstream regions, evaluate other surface water contaminants in surface and/or groundwater, and implement best management practices.
Advisor: Tiffany L. Messer