SIMULATION OF SEDIMENT AND PLANT NUTRIENT LOSSES BY THE CREAMS WATER-QUALITY MODEL

CREAMS was applied to a field-sized watershed planted to cotton in the Limestone Valley region of northern Alabama. The field was cultivated for three years with conventional tillage (CvT) followed by three yea rs of conservation tillage (CsT). CREAMS is composed of three componen ts: hydrology, erosion, and chemistry. Surface runoff and losses of se diment, N and P were simulated and results were compared with the obse rved data from the watershed. Curve numbers recommended in the CREAMS user's guide were not adequate for the watershed conditions. The hydro logy submodel improved runoff simulation from CvT and CsT when field-d ata based curve numbers were used. The erosion submodel demonstrated t hat CsT reduced sediment loss more than CvT, even though CsT had highe r runoff than CvT. The nutrient submodel based on the simulated runoff and sediment underpredicted N loss for both CvT and CsT. This submode l, however, accurately predicted P loss for CvT, but underpredicted fo r CsT (50 percent lower than the observed). The results of CREAMS simu lation generally matched the observed order of magnitude for higher ru noff, lower sediment, and higher N and P losses from CsT than from CvT .