Effect of flow velocity on phosphorus uptake by bed sediments

Abstract

The transport, transformation and ultimate fate of phosphorus (P) in river systems are significantly influenced by hydrodynamic conditions. To investigate the effect of flow velocity on the P uptake by bed sediments, a series of laboratory experiments are carried out in an incubator shaker and an annular flume. The results showed a much longer equilibrium time and a slower rate of P uptake by bed sediments in the flume than those in batch experiments. The process of P uptake by bed sediments was divided into two stages: (i) in the first 24 h, the amount of P uptake increased with the increasing flow velocity and (ii) after 24 h, flow velocity had no significant effect on P uptake by bed sediments. The amount of P uptake appeared fluctuating over different velocities. The paper presents a linear relationship between the P fraction in the bed sediments and the square root of time lapsed, which indicates that the diffusional process of P from water column to bed sediments is the dominant process in controlling the P uptake by bed sediments. The slope and intercept of the regression line were controlled by the flow velocity. Of the two models used to describe the process of P uptake by bed sediments, the Elovich Equation appeared to be better than the boundary layer model due to its ability to distinguish the different uptake rates at different flow velocities.