Multiple external and internal phosphorus (P) sources to an urban lake, Half Moon Lake in Wisconsin, were examined during the summer of 1999 in order to develop management strategies for effective P control and reversal of eutrophication (Trophic State Index=74). Internal recycling ofP accounted for 80% of the summer P budget of the lake. F1ux ofP from the sediment accounted formostofthe internal P loading ( 42% of total budget). However, decomposition of Potamogeton crispus and recycling of macrophyte P during the middle of the summer growing season, and P resuspension due to motor boat activity, accounted for 20% and 17% of the P budget, respectively, representing additional important sources to be controlled. In contrast, summer P loading via the watershed (storm sewers and precipitation) was much less. Using a water quality model (Bath tub), we found that reduction of internal P sources could substantially reduce by greater than 70% the high concentrations of algae in the lake (mean summer chlorophyll = 82 mg • m3 ). Suggested internal P control measures included a sediment chemical treatment to bind P, greater harvesting of P. crispus to reduce the macrophyte P pool at the time of senescence, and limiting motor boat activity when the lake is weakly stratified.

Lakes Planning Report

The City of Eau Claire proposes to examine the water quality conditions and nutrient budget for Half Moon Lake. Task Two activities include: 1) sampling and analysis of water from various lake depths, 2) sediment sample collection and incubation, and 3) calculation of soluble reactive phosphorus (SRP) release rates. The Department of Natural Resources will be provided with both paper and electronic copies of the final report. Project results will be shared with the public through presentations to community groups.

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