The uptake of Cu, Zn, and Cd by fresh water plankton was studiedby analyzing samples of water and plankton from six lakes in southernCalifornia. Co, Pb, Mn, Fe, Na, K, Mg, Ca, Sr, Ba, and Al were alsodetermined in the plankton samples. Special precautions were takenduring sampling and analysis to avoid metal contamination.
The relation between aqueous metal concentrations and theconcentrations of metals in plankton was studied by plotting aqueousand plankton metal concentrations vs time and comparing the plots.No plankton metal plot showed the same changes as its correspondingaqueous metal plot, though long-term trends were similar. Thus,passive sorption did not completely explain plankton metal uptake.
The fractions of Cu, Zn, and Cd in lake water which wereassociated with plankton were calculated and these fractions wereless than 1% in every case.
To see whether or not plankton metal uptake could depleteaqueous metal concentrations by measurable amounts (e.g. 20%) inshort periods (e.g. less than six days), three integrated rateequations were used as models of plankton metal sorption.Parameters for the equations were taken from actual field measurements.Measurable reductions in concentration within short times werepredicted by all three equations when the concentration factor wasgreater than 10^5. All Cu concentration factors were less than 10^5.
The role of plankton was regulating metal concentrationsconsidered in the context of a model of trace metal chemistry in lakes.The model assumes that all particles can be represented by a singlesolid phase and that the solid phase controls aqueous metalconcentrations. A term for the rate of in situ production ofparticulate matter is included and primary productivity was usedfor this parameter. In San Vicente Reservoir, the test case, the rate of in situ production of particulate matter was of the same order ofmagnitude as the rate of introduction of particulate matter by theinfluent stream.
