Determination of Equilibrium Phosphorus Concentration of Everglades Agricultural Area Canal Sediments Using Adsorption Isotherms and Incubation of Intact Sediment Cores.

Excess nutrients particularly phosphorus (P) from the Everglades Agricultural Area (EAA) of South Florida is thought to be the main cause for ecosystem changes in the Everglades. Years of P loading within the EAA has significantly impacted the surrounding canal sediments such that it can function as a source of P through internal loading. Equilibrium Phosphorus Concentration (EPC) measurements can be used to identify sediments either as P sources or sinks. The objectives of the study were to determine the EPC of sediments from three main EAA canals: Miami, West Palm Beach (WPB), and Ocean by (i) incubation of intact sediment columns, and (ii) adsorption isotherms. The mean EPC values for Miami canal sediments determined by intact sediment columns were 0.12 ± 0.03 mg L-1, for West Palm Beach canal 0.06 ± 0.03 mg L-1 and Ocean canal 0.08 ± 0.03 mg L-1. Slightly higher EPC values for the Miami canal sediments reflect the higher total P concentrations observed in the surface sediments. Overall the EPC values determined from adsorption isotherms were lower than those determined by intact sediment cores, possibly due to the absence of biotic transformations associated with plants and algae that may have transpired during the incubation experiment in the sediment column and the morphology of sediment layers which can affect P release.