Water Quality Modeling of Upper Mississippi River and Lake Pepin

There has been concern over the eutrophication in Lake Pepin in recent years, particularly following algal blooms and fish kills in 1988. Currently, the Metropolitan Wastewater Treatment Plant is the largest point source of phosphorus above the lake. In this study, the Environmental Protection Agency's EUTRO5 model was used to evaluate phosphorus control alternatives at the Metro Plant, using data from 1988, 1990, and 1991. Model results indicate that under summer low-flow conditions, the most optimistic improvement in Lake Pepin water quality would be to reduce the average chlorophyll a levels from 60 μg/L to 50 μg/L, still well above the goal of 30 μg/L. Chlorophyll a reductions are not expected under higher summer flow conditions such as those encountered in 1990 and 1991.