Author(s): A Saleh, PW Gassman, J Abraham, J Rodecap
The watershed-scale SWAT (Soil and Water Assessment Tool) and field-scale APEX (Agricultural Policy/Environmental eXtender) models were used to estimate flow and nitrate N (NO3-N) loads within the Upper Maquoketa River Watershed (UMRW). The UMRW is highly impacted by swine, cattle, and dairy operations. A GIS interface was used to generate much of the required data for the models. Simulation of manure applications at the field-scale was performed using APEX. The predicted flow and NO3-N loading from the manure application fields were then input into SWAT as direct point sources. The predicted flow and NO3-N loading obtained from SWAT were compared with measured flow and NO3-N data from four monitoring sites within the UMRW. Considering the size and variation of land use, land cover, geology, and soils within the UMRW, the predicted flow and NO3-N loading by SWAT fell reasonably well within the range of measured values.