Legacy Phosphorus Implications for the Recovery of Lake Okeechobee, Florida, USA Havens, Hans Paerl, K. Ramesh Reddy and R. Thomas J
Dec 14, 2015
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