The effect of flow patterns on uptake of phosphorus by river periphyton

The effect of various flow patterns on the uptake of 32 P by river periphyton was examined in a laboratory flume. In general, water movement increased 32 P uptake, except where the phosphorus demand of the microorganisms was presumably satisfied by molecular diffusion at high phosphorus concentrations (105 µ g·liter −1 PO 4 ‐P). However, there was little difference in 32 P uptake between the several distinct flow regimes produced by increasing or decreasing velocity and turbulence associated with a hump and hydraulic jump. It appears that the threshold limit for water movement, after which no further stimulation occurs, is ⩽5.4 cm·s −1 , the lowest velocity tested. A reduction in 32 P uptake by formaldehyde‐killed films of periphyton indicated that 50–75% of the uptake of the untreated films was due to biological activity.