P control projects since 1960s Fencing of waterways to prevent animal access Agricultural best management practices Dairy buy out program Dairy waste management systems Wetland treatment areas Various other advanced technologies
P loads vary from year to year but no long-term decline has occurred.
The difference between P input and P output is declining over time = reduced assimilation.
The concentration of TP in the lake has increased over 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 implications P 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