The restoration of Lake Apopka in relation to alternative stable states

Lake Apopka (Florida, USA) changed in 1947 from being a clear, macrophyte-d ominated lake, used primarily for fishing, into a turbid algal lake with a poor fishery. The lake has resisted various efforts to reverse the change a nd restore the previous state. The restoration approach emphasizes the redu ction in phosphorus inputs to reduce algal blooms and clear the water. We e xamined the question of whether a deep-lake approach with nutrient reductio ns is going to work on this large (area 124 km(2)) and shallow (mean depth 1.7 m) lake, or if techniques such as drawdowns or wind barriers developed for shallow lakes using the theory of alternative stable states are more ap plicable. The assumptions upon which the current restoration is based are not support ed. The poor transparency is due more to resuspended sediments than plankto n algae, so the current Secchi disk depth of 0.23 m is predicted to increas e to 0.34 m with any reasonable reduction in algal levels. The f ailure of the macrophytes to become re-established probably is due more to unstable s ediments than lack of light reaching the lake bed, and the marsh flow-way d eveloped by the St Johns River Water Management District will be ineffectiv e in removing particles from the lake. It would take more than 300 years to remove the fluid mud and more than 800 years to remove the rest of the low density sediments. We conclude that the loss of macrophytes in Lake Apopka is an example of a forward switch in the theory of alternative stable stat es, and that it will take more than a nutrient reduction program to bring a bout the reverse switch to a macrophyte state. We suggest an alternative ap proach using wave barriers to create refuges for plants, macroinvertebrates , and fish to restore Lake Apopka's largemouth bass fishery.