title: An investigation of the effects of water velocity on inorganic phosphorus influx to a sediment.
abstract: Measurements of the net influx of soluble reactive phosphorus (SRP), to a river bed-sediment, illustrate the importance of the water velocity and hydrodynamics in controlling the transfer rates. Experiments are reported using a characterised bed-sediment, with associated fauna, contained in a flowing-water channel. The results show a systematic increase in the net influx of SRP with increasing water velocity. A mathematical description of the influx was sought by modelling the experimental results using the Elovich equation, a boundary-layer model and a parabolic rate equation. In fact all three kinetic equations produce a good representation of the experimental data and it is concluded that further research is needed, in well-defined hydrodynamic conditions, to distinguish between the boundary-layer model and the parabolic equation. The boundary-layer model leads to an inverse relationship between the boundary-layer thickness (z/microm), and the water velocity (v/cm s(-1), viz z approximately 2500/v). In comparison, the parabolic equation of the form: influx of SRP (mol m(-2) = kp [SRP-EPC0]2, where EPC0 is the concentration at which the influx is zero prior to the sorption of phosphorus by the sediment and kp is the rate constant which leads to a velocity dependence, kp* = 0.714v + 1 where kp* is the reduced rate constant, kp* = kp(v)/kp(0). The semi-empirical Elovich equation in the form: influx of SRP (mol m(-2)) = (1/b) ln(1 + abt) where a and b are the Elovich parameters and t the time, gives a convenient description of the net influx of SRP to bed-sediments downstream of a point-source of pollution. The parameters calculated from the results obtained from the experimental channel are used to estimate the SRP flux to the sediment for a distance of up to 5 km downstream of a point-input of SRP.
authors.affiliation: Institute of Freshwater Ecology, River Laboratory, East Stoke, Wareham, Dorset, UK, BH20 6BB.
authors.forename: W A
authors.initials: WA
authors.lastname: House
authors.forename: F H
authors.initials: FH
authors.lastname: Denison
authors.forename: J T
authors.initials: JT
authors.lastname: Smith
authors.forename: P D
authors.initials: PD
authors.lastname: Armitage