Fate and Transport of Trace Organics and Antibiotic Resistance Genes in Agricultural Systems in Nebraska

Nebraska belongs to the US Corn Belt where grasslands are being increasingly converted to corn and soybean production. The amount of concentrated animal feeding operations (CAFOs) in Nebraska increased by 32% in 2017. This increased agricultural intensification has coincided with increased chemical inputs necessary for crop and animal production, including trace organic compounds such as pesticides, herbicides, antimicrobials, and steroid hormones, and increased the amount of manure produced, stored, and land applied. Trace organic compounds and manure constituents have been related to health and environmental concerns. Trace organics are considered endocrine disruptors, and manure constituents such as bacteria have developed resistance to antibiotics which is a public health concern. Knowledge of the fate and transport of these contaminants is of great importance to assess and control the risk posed by them. This dissertation investigates the fate and transport of one pesticide, three antibiotics, and antibiotic resistance genes (ARGs) in agricultural systems in Nebraska. Results show that due to repeated annual application, biodegradation of atrazine has been enhanced in agricultural soils in Nebraska. In such soils, the overall impact of increased infiltration rate on atrazine transport may be limited as the influence of degradation overwhelms the potential for enhanced transport with infiltrating water. The manure application timing affects the concentration of antibiotics and ARGs in surface runoff. An interval longer than 2 weeks between application and rainfall often significantly reduced the levels of antibiotics and ARGs tested in runoff except for tet(X). The vertical transport of ARGs was influenced by the presence of manure in the system. When manure was present in the system, the first-order attachment coefficient (ka) was noticeably affected, and the attachment coefficients varied with the ARGs as: erm(F) \u3e tet(O) \u3e erm(C) \u3e tet(Q). And finally, manure presence did not impact the microbial community structure, diversity, or resistome in the soil but did impact the microbial community in the leachate samples. Soil texture impacted the microbiome in the leachate samples; generally, the leachate samples from loam columns had a lower microbial diversity than sandy loam columns