Phosphate Equilibrium Between Stream Sediments and Water: Potential Effect of Chemical Amendments

Sediments often play an important role in the temporary storage and release of phosphorus (P) in streams, especiallystreams receiving municipal wastewater treatment plant (WWTP) effluent. The objective of this study was to evaluatesediment-aqueous phase P equilibrium in four Ozark streams, and to determine the effect of alum (Al2(SO4)3) and calciumcarbonate (CaCO3) on stream sediment-P interactions and content of exchangeable P. Stream physicochemical propertieswere significantly affected by the effluent discharge from the WWTPs; of particular interest to this study was that the increasein P concentrations varied greatly among streams. Phosphorus inputs from WWTP significantly increased sedimentequilibrium P concentrations (sediment-EPC0) and readily exchangeable sediment-bound P, while decreasing the Pbuffering capacity of stream sediments. Sediment-EPC0 values were as great as 7 mg L-1 downstream from one WWTP,suggesting that sediments are a transient storage pool of P and may release P back into the stream system when P inputs fromthe WWTP are reduced. The addition of alum and CaCO3 significantly reduced the sediment-EPC0 and readily exchangeableP, while increasing the ability of sediments to buffer increasing P loads.