Groundwater nitrate depletion in a swine lagoon effluent-irrigated pasture and adjacent riparian zone

ABSTRACT: Irrigation of anaerobic swine lagoon effluent onto cattle-grazed grass pastures represents a common waste treatment method in the Coastal Plain of North Carolina. However, such treatment strategies can result in high nitrate (NO3) concentrations in the shallow ground-water beneath spray fields, and ultimately surface waters receiving groundwater discharge if application rates exceed crop and animal removal. This study was conducted to determine NO3 accumulation and movement in the spray fields and riparian zone on a swine farm in eastern North Carolina, as well as effects of effluent irrigation on streams recharged by shallow ground-water flow. Increases in the NO3 concentration of receiving streams occurred over the farm, suggesting that some NO3 was reaching surface waters. Despite evidence of denitrification losses in riparian areas, the riparian zone did not fully protect the receiving streams from high concentrations of NO3 in the groundwater.