Date Full Report Received


Date Abstract Report Received



Primary Investigator:


Hunt, P. G., T. A. Matheny, and K. C. Stone. "Denitrification in a Coastal Plain Riparian Zone Contiguous to a Heavily Loaded Swine Wastewater Spray Field." Journal of Environmental Quality, v33, no. 6 (2004): 2367-74.

Riparian zones are recognized worldwide as important landscape features that are able to buffer streams from pollutants, particularly nitrogen. The objectives of this experiment were to 1) assess the denitrification potential within this riparian zone and 2) determine the influence of various physical, chemical, and landscape features on denitrification. This experiment was conducted from 1994 to 1997 in North Carolina on a riparian zone contiguous to a spray field that was heavily loaded with swine lagoon wastewater. The acetylene blockage method was used for denitrification enzyme assays (DEA) on soils collected in cores (25 by 155 mm) on 13 dates from 1) the soil surface, 2) midway between the soil surface and water table, and 3) above the water table. Values of DEA ranged from 3 to 1660 g/kg/hr. DEA values were highest next to the stream and lowest next to the spray field. Throughout the riparian zone, nitrate was generally found to be the limiting factor for denitrification. Values of DEA generally decreased with soil depth; means for the surface, middle, and bottom depths were 147, 83, and 67 g/kg/hr, respectively. These DEA values are much higher than those commonly reported for riparian zones adjoining cropland of the Southeastern USA, but they are lower than those reported for constructed wetland used for treatment of swine wastewater in the region. In a stepwise regression of log DEA, soil total nitrogen was found to be the most highly correlated factor (r2 = 0.64). However, inclusion of water table depth, soil sample depth and distance from the spray field gave improvements in the predictive capability (r2 = 0.86). This riparian zone possessed sufficient soil area with high denitrifying conditions to be a significant factor in the removal of excess nitrogen in the groundwater.