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

Abstract

Nonpoint source pollution of surface and groundwater resulting from agricultural management practices is amajor water quality problem. This problem was assessed on a demonstration watershed in the Cape Fear River 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 concentrations 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. Nitrate-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, respectively, 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 nitrate-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.