Prediction of the quality of water in a proposed impoundment in Southwestern Wisconsin, USA

Abstract

The probable quality of water in a large multipurpose impoundment under construction in the driftless area of southwestern Wisconsin was determined by using stream monitoring data, statistical information, and literature values for point and nonpoint nutrient loading. The impoundment drainage basin is largely rural, and much of the area slopes steeply. Point sources of N and P (sewage treatment plants and farmyards) are small relative to nonpoint sources (runoff from agriculture and forest lands). Stream flow and nutrient concentration are positively related. The major fraction of the nutrient input is from runoff from snowmelt and from early summer storms. The calculated annual loadings of total N and total P were compared to accepted static and dynamic models to predict the resultant water quality. These comparisons indicated that the impoundment would be heavily overloaded with P and so would be highly eutrophic. Owing to the nonpoint nature of the nutrient sources, they would be difficult and expensive to control. Partly as a result of this assessment, further funding for the impoundment was withdrawn.