Sediment Control of Soluble Reactive Phosphorus in Hoxie Gorge Creek, New York

Abstract

Stream sediments were found to regulate the soluble reactive phosphorus (SRP) of stream water by geochemical processes. This conclusion was based on sediment analysis, laboratory sorption experiments, and measurement of the equilibrium phosphorus concentration (EPC). EPC is the concentration of P in the water at which there is neither sorption nor desorption of P by the sediments. At low flow conditions, streamwater SRP was highly correlated with EPC at six sites along Hoxie Gorge Creek (r = 0.979). EPC was inversely related to the ionic strength of the equilibrating solution, with Ca2+ producing larger changes than Na+. Minimum EPC values occurred near the neutral pH of the stream water and increased sharply in acidic and basic solutions. Also, EPC was negatively correlated with the exchangeable Al content of the sediments at the six sites. These data are consistent with a mechanism previously verified for soils in which solution cations displace exchangeable Al(III) from sediments; hydrolyzed Al(III) reacts with phosphate and removes it from solution. EPC and streamwater SRP were lower at sites with sediments that had higher concentrations of P-binding sites, despite also having higher sediment P.