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Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007

LAKE HANCOCK SEDIMENT REMOVAL MESOCOSM EXPERIMENT- PRELIMINARY RESULTS

Dave Tomasko, Emily Hyfield, and Doug Robison PBS&J Tampa, FL

Lake Hancock, a 4,500-acre freshwater lake, is located in Polk County, Florida at the headwaters of the Peace River. Historically, this lake has experienced poor water quality for at least the past 40 years, and is currently listed (303(d)) as an impaired water body based on dissolved oxygen and nutrients (TSI>60). Under a contract with Polk County Natural Resources, PBS&J completed the first of two mesocosm experiments at three locations in the lake to assess the potential for water quality improvements based on sediment removal activities. The funding for this project was provided by Polk County and FDEP for the creation of the TMDL BMAP. The initial experiment was completed in Winter 2006; a second one will be repeated in Summer 2007. Three mesocosm conditions were sampled: Dredged, Undredged and Reference, at each of three locations. Samples were taken on four dates, two under natural conditions, and two under “mixed” or artificially induced windy conditions. A suite of physical, chemical and biological water quality parameters were analyzed. Preliminary results indicate a significant change in nutrient concentrations between the dredged and undredged mesocosms. Changes in nutrient concentrations indicate a shift in the Total Nitrogen:Total Phosphorus ratio which, if sustained, could reduce blue-green algal dominance. Based on BOD results and the relationship between Lake Hancock discharges and DO in the Peace River at Bartow, the potential benefit from dredging the lake could extend into the Upper Peace River as well.

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NOTES

Session 8A – Page 3

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