Applications of delta-nitrogen-15, delta-oxygen-18 of nitrate to waste storage effectiveness in mantled karst terrain, northwestern Arkansas

Animal production is the predominant agricultural practice in northwestern Arkansas because the thin, rocky soils are unsuitable for sustainable crop production. Waste-storage lagoons at CAFOs are a potential source of ground water contamination. NRCS has developed Conservation Practice Standard code 313 to reduce the risk of ground water contamination from such storage systems. Data were collected to determine the effectiveness of a swine finisher unit's lagoon, constructed to the NRCS standard, at the University of Arkansas Savoy Experimental Watershed. Seepage, <1.5 mm/day, was computed using a water budget. delta15N and delta18O of NO 3 in interceptor trenches suggest lagoon overflow. NO3, Cl, and SO4 concentrations at an epikarst seep suggest a nearby anthropogenic source. NO3 concentrations in wells down-gradient of the seep are <3 mg/L, suggesting dilution. Enrichment of measured delta15 N vs. modeled delta15N along the flow path suggests denitrification and/or vegetative uptake are mechanisms for NO3 attenuation in the interflow zone.