Implications for the Recovery of Lake Okeechobee, Florida, USA Karl Havens, Hans Paerl, K. Ramesh Reddy and R. Thomas James.

Legacy PhosphorusImplications for the Recovery of Lake Okeechobee, Florida, USA

Karl Havens, Hans Paerl, K. Ramesh Reddy and R. Thomas James

OutlineGeographic and historical setting

Phosphorus reduction programs

Loading and lake TP responses

Watershed and lake P mass balances

Effects of legacy phosphorus

Implications for management

Lake Okeechobee, FLArea 1,730 km2

Mean Depth 2.7 mMax Depth 5 m

Emergent Wetland

Source: South Florida Water Management District

P control projects since 1960s

Fencing of waterways to prevent animal access

Agricultural best management practices

Dairy buy out programDairy waste management systemsWetland treatment areasVarious other advanced technologies

P loads vary from year to year but no long-termdecline has occurred.

The difference between P input and P outputis declining over time = reduced assimilation.

The concentration of TP in the lake has increasedover time, except in recent drought years.

In shallow shoreline areas that support SAV, fish habitat, and most human uses, water quality and biological conditions are excellent when the lake depth is low, regardless of high P out in the deeper mid-lake region.

Why have the lake and watershed not responded to all the P reduction measures?

Legacy phosphorus in the soils, wetlands and lake sediments – phosphorus that accumulated there over decades when there was high export from agricultural lands, and is now slowly leaching back into the surface water.

Management implicationsP control measures up in the watershed will

not achieve load reduction for decades or longer

More immediate P reduction would require large-scale wetland treatment right at the lake

Lake sedimentary P still will delay recovery

Yet there is an opportunity to achieve good conditions for fish, SAV, and users in near-shore area if lake depths can be kept low, perhaps through large-scale storage of water in the basin

Thank you