GLEAMS SIMULATION OF GROUNDWATER NITRATE-N FROM ROW CROP AND SWINE WASTE-WATER SPRAY FIELDS IN THE EASTERN COASTAL-PLAIN

Nonpoint source pollution of surface and groundwater resulting from ag ricultural management practices is a major water quality problem. This problem was assessed on a demonstration watershed in the Cape Fear Ri ver Basin of North Carolina, during a five-year study. Groundwater was monitored in a row crop field (corn/wheat/soybean) and a swine waste spray field (Coastal bermuda grass). Groundwater nitrate-N concentrati ons averaged 6.5 mg/L in the row crop field. Nitrate-N concentrations in groundwater at the swine waste spray field exceeded 80 mg/L. Nitrat e-N concentrations were simulated in both fields with the GLEAMS model . The GLEAMS model simulated groundwater nitrate-N concentrations with mean residuals (simulated-observed) +/-1.3 mg/L and +/-19 mg/L, respe ctively for the row crop and the swine waste spray field. Groundwater nitrate-N concentrations have been reduced in the spray field by using improved management practices and the GLEAMS model simulated this nit rate-N concentration reduction. These simulation results show that the GLEAMS model can be used to predict nitrate-N loading of groundwater of these agricultural management systems.