Assessing the impact of Veterinary Antibiotic species on Treatment Wetland Nutrient Removal at the Mesocosm Scale

Natural and constructed wetlands are now frequently used across the United States for mitigating nitrate losses to both surface and groundwater. Though the use of wetlands as a treatment approach for nitrate in runoff is well known, other active contaminants regularly co-occur with nitrate, potentially affecting the efficacy of nitrate-N removal. For example, veterinary pharmaceuticals have been observed in runoff originating from fields that receive livestock facility animal waste. In 2022, two mesocosm experiments were conducted to evaluate the combined effects of 4 common-use veterinary antibiotics (VAs) (chlortetracycline, sulfamethazine, lincomycin, monensin) on nitrate-N reduction efficiency. We hypothesized veterinary antibiotics would significantly impact nitrate-N removal through changes in denitrification processes within wetland ecosystems. To test this hypothesis, we simulated two pulse-flow storm events (2.5mg N0₃-N/L, 7.5 mg N0₃-N/L) and quantified the combined effects of trace-level antibiotics (1.0 mg/L) on the nitrogen cycle in fully saturated treatment wetlands. Results from previous experiments we conducted suggest nitrate reduction rates in treatments receiving antibiotics (CA= -1.04, FTWA= -1.31) remove nitrate more efficiently than those without (C= -0.01, FTW= -0.52). Plant uptake of VAs was also assessed, with results indicating that accumulation of VA compounds in wetland plants occurs and is primarily limited to the below ground biomass (Above ground= 0.59mg per plant, Below ground=206.66mg per plant) and the antibiotic species. Findings from these experiments will provide new insight into whether antibiotic residues in wetland environments affect proposed mitigation strategies for controlling nitrogen losses from fertilized crops and managing nitrate contamination of ground and surface water.