Phosphorus Sorption Capacities of Wetland Soils and Stream Sediments Impacted by Dairy Effluent

Abstract

AbstractThe 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 capacity 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 conditions 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 maxima. 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%.