Using SWAT for sub-field identification of phosphorus critical source areas in a saturation excess runoff region

Abstract

The identification of phosphorus critical source areas (CSAs) is an important step in reducing nonpoint-source phosphorus contributions to lakes and streams, providing the basis for targeted mitigation and efficient utilization of limited resources. A high-resolution SWAT model, consisting of sub-field level hydrologic response units, was applied to Lake Champlain’s Missisquoi Bay Watershed, located along the United States–Canadian border. Because this region of the northeastern United States is dominated by saturation excess runoff, a novel approach for adjusting SCS (Soil Conservation Service) curve numbers based on the local compound topographic index was developed. After calibration and validation, the SWAT model was run for a 30-year period to identify the phosphorus CSAs throughout the watershed, determining that 20% of the watershed produces 74% of the total phosphorus load. The resulting sub-field level CSA map is currently being hosted online, providing a valuable tool for natural resources planners, land owners, and scientists. Editor Z.W. Kundzewicz; Guest editor V. Krysanova