Phosphorus sorption capacities of wetland soils and stream sediments impacted by dairy effluent

The ability of stream sediments and adjacent wetlands to retain added P depends on the P sorption capacity and physico-chemical properties of sediments or wetland soils, The objectives of this study were to: (i) determine the potential P sorption capacities of wetland soils and stream sediments in systems with distinctly different P loadings, and (ii) establish the relationship between P sorption rapacity and selected physico-chemical properties. Batch sorption isotherms were measured under aerobic and anaerobic conditions for sediments and wetland soils along a stream-wetland-upland continuum at two sites in the Lower Kissimmee River Basin and Taylor Creek/Nubbin slough of the Okeechobee Basin, Florida. Soluble P and equilibrium P concentrations (EPC) of stream sediments generally decreased along the wetland-upland continuum, The EPC values were about twofold greater under anaerobic renditions than aerobic conditions; however, P sorption capacities decreased by about 35% under anaerobic conditions compared with aerobic conditions. The P sorption maxima, estimated by a single point isotherm measured at an added P level of 1000 mg P kg(-1), correlated well with Langmuir adsorptive mar;ima. Phosphorus retention by stream sediments and wetland soils was strongly correlated with contents of amorphous and poorly crystalline forms of Fe and Al, which explained 87% of the variability in P retention maximum. Addition of total organic C to predictive equations improved the predictability by only 5%.