Cycling of Zinc‐65 by Coliumbia River Periphyton in a Closed Lotic Microcosm1

Studies of 65Zn cycling by periphyton were performed in a closed, lotic microcosm under varying light regimes, community state, initial ambient concentrations, and stable divalent cation concentrations. Uptake of 65Zn was considerable in continuous light, continuous darkness, a 12‐hr photoperiod, or by killed communities, indicating a dominant adsorptive uptake mechanism. Uptake of 65Zn was shown to be proportional to the initial ambient concentration of 65Zn, which decreased during the course of an experiment. Increasing the concentration of stable zinc or magnesium proportionately decreased the uptake of 65Zn, illustrating a competition for binding sites and supporting the adsorptive uptake theory. A discussion of the significance of this work to the reporting of concentration factors is presented. The similarity in function between the heterogeneous periphyton community and unialgal cultures or single species of plants is pointed out.