lake water quality model study for big green lake (1999)

In 1998, the Green Lake District received a lake protection grant from the DNR to complete a diagnostic feasibility study. One component of the diagnostic study process was the development of a water and nutrient budget for the lake as well as a water quality model. The model will be used in the goal setting process to evaluate the impact of watershed pollutant load reduction on water quality improvement. Based on the results of the analysis the following conclusions were made:

1. The surface total phosphorus concentration in Big Green Lake does not significantly different at various points across the lake.
2. Based on the spring total phosphorus concentration Big Green Lake is eutrophic.
3. Big Green Lake's chlorophyll-a response to total phosphorus is less than what regional regression equations would predict.
4. The lake's low chlorophyll-a response may be the result of food web
5. Based on monitored flow, sediment and total phosphorus loading, 1997 was close to an average year for the lake, while 1998 was below average.
6. Silver Creek contributes the greatest annual total phosphorus loading to Big Green Lake at approximately 44% of the total and 50% of the tributary loading.
7. The Southwest Inlet is the second greatest source of total phosphorus loading at 13% of the total and 15% of the tributary input.
8. The watershed unit area total phosphorus export values for the Silver Creek watershed fall into the lower portion of the range monitored for agricultural land in Wisconsin.
9. Monitoring data indicate that no significant bypassing of Silver Creek's inflow loading is occurring.

Based on the above conclusions it was recommended that:

1. An in-lake total phosphorus goal be established for Big Green Lake in the near future.
2. Watershed modeling be conducted to identify total phosphorus loading source areas and BMP strategies for load reduction.
3. The BMP implementation strategy be supported by watershed modeling and be sufficient to meet the in-lake water quality goal.
4. In-lake and tributary monitoring be continued to document Big Green Lake’s water quality response to land management activities.

View the full lake water quality model study for Big Green Lake.

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