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

lIrrigation of anaerobic swine lagoon effluent onto cattle-grazed grass pas tures represents a common waste treatment method in the Coastal Plain of No rth Carolina. However, such treatment strategies can result in high nitrate (NO3) concentrations in the shallow groundwater beneath spray fields, and ultimately surface waters receiving groundwater discharge if application ra tes exceed crop and animal removal. This study was conducted to determine N O3 accumulation and movement in the spray fields and riparian zone on a swi ne farm in eastern North Carolina, as well as effects of effluent irrigatio n on streams recharged by shallow groundwater flow. Increases in the NO3 co ncentration of receiving streams occurred over the farm, suggesting that so me NO3 was reaching surface waters. Despite evidence of denitrification los ses in riparian areas, the riparian zone did not fully protect the receivin g streams from high concentrations of NO3 in the groundwater.