PARTICULATE PHOSPHORUS REMOVAL VIA WETLAND FILTRATION - AN EXAMINATION OF POTENTIAL FOR HYPERTROPHIC LAKE RESTORATION

Lake Apopka in Florida, USA, is a large (area = 124 km2), hypertrophic (mean total phosphorus = 0.220 g/m3; mean chlorophyll a = 60 mg/m3) lake, with a large sedimentary store of available P (1635 x 10(6) g P). Phosphorus loading from floodplain farms (132 x 10(6) g P/yr) has been the primary cause of eutrophication, Assuming elimination of farm P loading, the Vollenweider model predicts a decline in equilibrium P concentration from 0.270 to 0.024 g/m3, if the P sedimentation coefficient (sigma) remains constant. It is likely, however, that the value for sigma will fall with the elimination of farm loading due to unabated internal P loading from the sediments. Under a worst-case scenario (sigma = 0), the model predicts that exportation of P from the lake via wetland filtration will greatly accelerate the lake's recovery. Recirculation of lake water through a 21-km2, created wetland and elimination of farm P loading is projected to result in a negative P balance for the lake (-23 x 10(6) g P/yr) leading to depletion of P stores in the lake in about 60 yr. The estimated cost of the project, $20 million, is less than 3% of the estimated cost of dredging. A 3.65-km2 demonstration project is underway to test and refine the wetland filtration technique. We believe the technique could be cost-effective for other hypertrophic lakes.