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 o f sediments or wetland soils, The objectives of this study were to: (i ) determine the potential P sorption capacities of wetland soils and s tream sediments in systems with distinctly different P loadings, and ( ii) establish the relationship between P sorption rapacity and selecte d 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 Kis simmee River Basin and Taylor Creek/Nubbin slough of the Okeechobee Ba sin, Florida. Soluble P and equilibrium P concentrations (EPC) of stre am sediments generally decreased along the wetland-upland continuum, T he EPC values were about twofold greater under anaerobic renditions th an aerobic conditions; however, P sorption capacities decreased by abo ut 35% under anaerobic conditions compared with aerobic conditions. Th e 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 ad sorptive mar;ima. Phosphorus retention by stream sediments and wetland soils was strongly correlated with contents of amorphous and poorly c rystalline forms of Fe and Al, which explained 87% of the variability in P retention maximum. Addition of total organic C to predictive equa tions improved the predictability by only 5%.