Veterinary antibiotic, pathogen, and antibiotic resistance genes in tile effluent and shallow groundwater following manure application: Influence of controlled tile drainage
Agriculture and Agri-Food Canada, Ottawa
Chlortetracycline, tylosin, and tetracycline (plus transformation products), and DNA-based Campylobacter spp. and tetracycline antibiotic resistant gene (tet(O)) in tile drainage and shallow (1.2 to 2m depth) groundwater were examined following a autumn liquid swine manure application on clay loam plots under controlled (CD) and free (FD) tile drainage. The chlorotetracyline transformation product iso-chlortetracycline was the most persistent veterinary antibiotic (VA) analyte in water. Rhodamine WT (RWT) tracer was mixed with manure and monitored in tile and groundwater. RWT and VA concentrations were strongly correlated in water. While CD reduced tile discharge and eliminated application-induced VA movement to tile drains, total VA mass loading from tile was not affected significantly by CD. At CD and FD test plots, the biggest ‘flush’ of VA mass and highest VA concentrations occurred in response to precipitation received 2d after application, which strongly influenced the flow abatement capacity of CD on account of highly elevated water levels in field initiating overflow drainage for CD systems (when water level <0.3m below surface). VA concentrations in tile and groundwater became very low within 10 d following application. Both Campylobacter spp. and tet(O) genes were present in groundwater and soil prior to application, and increased thereafter. Unlike the VA compounds, Campylobacter spp. and tet(O) gene loads in tile drainage were reduced by CD, in relation to FD; which was consistent with how CD mitigated loading of fecal indicator bacteria over the study period.