|SREL Reprint #0715|
Relative Mobilization of Zinc, Cerium, and Americium from Sediment in an Aquatic Microcosm
P. Giesy and Richard A. Geiger
The effect of rooted aquatic macrophytes on the relative mobility of 65Zn,
144Ce, and 241Am from sediment was investigated in
sediment – water microcosms. The presence of macrophytes resulted in a greater total above
sediment biomass and reduced seston and aufwuchs biomass.
Macrophytes also increased the total mass of all three elements in the
above-sediment components. This increase was not caused solely by increased biomass into
which the isotopes could partition since concentrations of all three isotopes
were increased in the water, seston, and aufwuchs as a result of the presence of
macrophytes. The ratio of Am to 144Ce
was the same in seston, aufwuchs, and macrophytes when macrophytes were present.
The presence of macrophytes caused a reduction of Am relative to 144Ce
in the water, seston, and aufwuchs. The
dynamics of 65Zn were different from those of 144Ce and 241Am.
The ratio of 241Am to 65Zn was approximately
sevenfold greater in seston, aufwuchs, and macrophytes than in sediments or
water, with macrophytes causing a significant increase in this ratio only in
water. Even though the sediments
contained a large quantity of stable zinc, the observed behavior of 65Zn
could not be attributed to isotope dilution.
Rather 65Zn seems to be restricted from uptake by biota,
relative to 241Am and 144Ce. The microcosms studied here were sufficient to study the
relative mobility of trace elements from sediments, as well as specific pathways
of mobilization, but were not useful for measuring the rate and absolute
magnitude of elemental fluxes from sediments, which could be extrapolated to
SREL Reprint #0715