Nonpoint source pollution from agriculture has been a major concern, particularly where intensiveagricultural operations exist near environmentally sensitive waters. To address these concerns, a water quality projectwas initiated in Duplin County, North Carolina, in the 2044-ha Herrings Marsh Run watershed. A swine farm within thismonitored watershed expanded its operation from 3,300 to more than 14,000 animals. Groundwater nitrate-N increasedsignificantly in three of the seven wells located adjacent to the spray field and in the adjoining riparian zone. Streamnitrate-N concentrations have increased after the expansion of the swine operation in the colder months, butconcentrations have remained approximately the same during the warmer months. Stream ammonia-N meanconcentrations after expansion have increased as well as the frequency and magnitude of ammonia-N concentrationspikes. Ortho-phosphate concentrations in the stream water have been relatively consistent over the study period. Theriparian zone is reducing the impact of spray field groundwater nitrate concentrations and ammonia loadings in anadjacent stream.
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Stone et al. (1998) studied this question.