Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Environmental Dynamics (PhD)

Degree Level



Environmental Dynamics


Phillip D. Hays

Committee Member

John V. Brahana

Second Committee Member

Wen Zhang


Applied sciences, Health and environmental sciences, Earth sciences, Antibiotic resistance, Arkansas, Concentrated animal feeding operations, Epikarst, Groundwater, Karst, Nutrients


Organic matter (OM) in the environment acts as a nutrient, but may also act as a transport vector for harmful chemical compounds and bacteria. Acetate is a labile form of OM produced during fermentation in anaerobic lagoons used to store animal fecal-waste from concentrated animal feeding operations (CAFOs). Dry and liquid fertilizers from CAFOs pose a threat to groundwater by introducing excessive amounts of nutrients (e.g. OM, nitrate and ammonia), metals, and antibiotic compounds. In the epikarst of Northern Arkansas in the Buffalo River watershed additional input of labile dissolved organic carbon (DOC) from liquid CAFO waste-fertilizers was hypothesized to increase microbial activity along groundwater flowpaths. In addition, high metal and antibiotic concentrations associated with increasing concentrations of DOC were hypothesized to be detrimental to microbial processes, with exception given to resistant bacteria species. Laboratory microcosm experiments were conducted to characterize microbial DIC production and denitrification. The microcosms were treated with acetate, nitrate, phosphate, and/or various metal species to characterize concentration effects on microbial activity. Field studies were used to calibrate laboratory conditions, and to compare biomass production and composition. Isotopes of dissolved inorganic carbon (δ13C-DIC), nitrate (δ15N-NO3), and dissolved oxygen (DO) were used to assess microbial responses to increasing DOC concentrations. Fatty acid methyl ester (FAME) analysis was used to characterize biomass produced during the experiments.

Conversion of DOC-DIC and decreasing NO3 concentrations were observed in the microcosms. Microbial productivity was greatest when DOC concentrations were 10 times greater than NO3 concentrations. When metals were added to the microcosms, microbial activity was inhibited with exception being microcosms containing metal concentrations below 10 µg/L. FAME biomarkers indicated gram-negative bacteria were present in biomass samples from the spring orifice and metal-treated microcosms, but microcosms amended with nutrients and DOC displayed indicators of predominantly gram-positive bacteria. Critical findings of this study were: bacteria species transported in spring discharge were resistant to antibiotics and metals, high concentrations of DOC and nitrate increase biological productivity in epikarst and metal exposure inhibits nitrate removal and causes ecological shifts in biofilms selecting for resistant bacteria strains.