Sediment removal by the Lake Apopka marsh flow-way

Abstract

We review the evidence showing that the high turbidity levels of Lake Apopka are due primarily to resuspended sediments rather than phytoplankton, and that this situation is likely to persist unless there is a fundamental change in the lake. We discuss the reasons why reductions in phosphorus inputs, the gizzard shad removal program, and macrophyte plantings would not bring about such a change. Potentially the marsh flow-way could remove the flocculent sediments because of a unique combination of a very large surface area (125 km2), a mean depth of only 1.7 m, a layer of easily resuspended fluid mud, and a marsh flow-way that is designed to filter the lake volume about 2 times a year. Using several different estimates of the rate of sediment formation in the lake, our model calculates that it would take from 275 to 502 years to remove the sediments, so the lake could not attain clear water in a reasonable length of time. The model is mathematically correct but will give nonsense results if one tries to calculate removal times when the lake is accumulating sediments rather than losing them.