Eutrophication is a common problem for lakes in agricultural and urban areas, such as Lakes Wingra and Mendota in Madison, Wisconsin. This report describes a study to estimate the sources of phosphorus, a major contributor to eutrophication, to Lakes Wingra and Mendota from two small urban residential drainage basins. The Monroe Basin empties into Lake Wingra, and the Harper Basin into Lake Mendota. Phosphorus data were collected from streets, lawns, roofs, driveways, and parking lots (source areas) within these two basins and were used to estimate loads from each area. In addition to the samples collected from these source areas, flow-composite samples were collected at monitoring stations located at the watershed outfalls (storm sewers); discharge and rainfall also were measured. Resulting data were then used to calibrate the Source Loading and Management Model (SLAMM, version 6.3, copyright 1993, Pitt & Vorhees) for conditions in the city of Madison and determine within these basins which of the source areas are contributing the most phosphorus. Water volumes in the calibrated model were calculated to within 23 percent and 24 percent of those measured at the outfalls of each of the basins. These water volumes were applied to the suspended-solids and phosphorus concentrations that were used to calibrate SLAMM for suspended-solids and phosphorus loads. Suspended-solids loads were calculated to be within 4 percent and 17 percent, total-phosphorus loads within 24 percent and 28 percent, and dissolved-phosphorus loads within 9 percent and 10 percent of those measured at the storm-sewer outfall at the Monroe and Harper basins, respectively. Lawns and streets are the largest sources of total and dissolved phosphorus in the basins. Their combined contribution was approximately 80 percent, with lawns contributing more than the streets. Streets were the largest source of suspended solids.
Additional publication details
USGS Numbered Series
Sources of phosphorus in stormwater and street dirt from two urban residential basins in Madison, Wisconsin, 1994-95
Water-Resources Investigations Report
U.S. Dept. of the Interior, U.S. Geological Survey ;
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