Comparison of the uptake of inorganic phosphorus to a suspended and stream bed-sediment

Results are presented describing the influx of soluble reactive phosphorus (SRP) to a stream sediment in an outdoor experimental channel, a laboratory channel and in well-mixed suspensions. The kinetics of phosphorus uptake are modelled using several kinetic equations including the Elovich, Bangham, diffusion and first-order equation. The Elovich equation is found to describe best the SRP influx to both bed and suspended sediments. The relative contribution of abiotic and biotic processes in the outdoor experimental channel are considered together with estimates of the flux to the bed-sediment predicted from the results describing the kinetics in the laboratory channel. The sediment is characterized by mineralogy, size fractionation and wet-chemical analyses including total phosphorus, iron and calcium determinations as well as biologically available phosphorus (BAP) by the iron-oxide stripping method and the equilibrium phosphate concentration, EPC0, calculated from sorption measurements. The kinetic results from this sediment illustrate the importance of suspended sediment in the fast uptake of SRP. This contrasts with the control of the influx of SRP to the bed-sediment in channels with low concentrations of suspended solids, caused by the rate-limiting diffusional transfer across the sediment-water interface.