Wa. House et al., AN INVESTIGATION OF THE EFFECTS OF WATER VELOCITY ON INORGANIC PHOSPHORUS INFLUX TO A SEDIMENT, Environmental pollution, 89(3), 1995, pp. 263-271
Measurements of the net influx of soluble reactive phosphorus (SRP), t
o a river bed-sediment, illustrate the importance of the water velocit
y and hydrodynamics in controlling the transfer rates. Experiments are
reported using a characterised bed-sediment, with associated fauna, c
ontained in a flowing-water channel. The results show a systematic inc
rease in the net influx of SRP with increasing water velocity. A mathe
matical description of the influx was sought by modelling the experime
ntal 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 equa
tion, The boundary-layer model leads to an inverse relationship betwee
n the boundary-layer thickness (z/mu m), and the water velocity (v/cm
s(-1), viz z approximate to 2500/v). In comparison, the parabolic equa
tion of the form: influx of SRP (mu mol m(-2)) = k(p) [SRP-EPC(0)](2),
where EPC(0) is the concentration at which the influx is zero prior t
o the sorption of phosphorus by the sediment and k(p) is the rate cons
tant which leads to a velocity dependence, k(p) = 0.714v + 1 where k(
p) is the reduced rate constant, k(p)* = k(p)(v)/k(p)(0). The semi-em
pirical Elovich equation in the form: influx of SRP (mu mol m(-2)) = (
1/b) ln(1 + abt) where a and b are the Elovich parameters and t the ti
me, gives a convenient description of the net influx of SRP to bed-sed
iments downstream of a point-source of pollution. The parameters calcu
lated from the I results obtained from the experimental channel are us
ed to estimate the SRP flux to the sediment for a distance of up to 5
km downstream of a point-input of SRP.