Publication Type: Oral PresentationAbstract: Karst hydrology is characterized by multiple springs, sinkholes, and losing streams resulting from acidic water percolating through limestone. These features provide direct connections between surface water and groundwater and generally increase the risk of groundwater and stream contamination. Anthropogenic activities (agriculture, tourism, urban areas, and residential areas) accentuate the contamination potentials. The Soil and Water Assessment Tool (version 2005) was calibrated for the James River Basin, a large watershed (3,600 km2) in Southwest Missouri, to evaluate its ability to simulate flow and pollutant transport in karst areas. Losing streams were simulated by specifying high soil conductivities in the channels and springs were simulated as point sources. The model was calibrated for flow, phosphorus and bacteria using data from four weather stations, five flow gauges and four water quality stations. Results indicated that flow calibration is satisfactory in the main stream reaches but needs to be improved in the upper reaches. Pollutant calibration was acceptable on a frequency basis. The model was then utilized to estimate the magnitude of the contributions from each source of pollution and the potential impact of mitigation strategies. Understanding the assumptions and the limitations is necessary to determine the future development needs of the SWAT model in this domain and to interpret the results obtained with the current version.