Phosphorus storages in historically isolated wetland ecosystems and surrounding pasture uplands

Historically isolated wetland ecosystems may provide a phosphorus (P) storage sink for runoff from agricultural pastures. Four historically isolated wetlands were characterized on two cow-calf ranches in the Lake Okeechobee Basin, Florida, to (i) quantify P storage in ecosystem compartments (plant biomass, litter, and soil) of historically isolated wetlands and surrounding improved pasture uplands, (ii) determine if a P storage gradient existed with landscape position, and (iii) evaluate the potential to increase wetland ecosystem P storage if these wetlands are hydrologically restored. The hydroperiod for the wetlands studied ranged between 241 and 315 days. In general, more P was stored in wetland plant biomass and soil than in the corresponding upland compartments. Surface soils (0-10 cm) were by far the largest reservoir of P (> 87%), and soil organic matter accounted for > 69% of the variability in wetland soil total P. The amount of P stored in these wetlands could be increased by applying nitrogen (N), as the above-ground wetland plant biomass was N limited. Better alternatives for longer-term increases in P storage should promote increased accumulation of soil organic matter in wetland soils. Wetland hydrologic restoration that resulted in an increase in wetland area of between 5 and 20% could potentially increase wetland ecosystem P storage by up to 13 kg P ha(-1).