RELEASE RATES OF TRACE-ELEMENTS AND PROTEIN FROM DECOMPOSING PLANKTONIC DEBRIS .1. PHYTOPLANKTON DEBRIS

The release rates of Ag, Am, Cd, Ce, Co. Pb, Se and Zn from decomposin g diatom cells were determined using gamma-emitting radiotracers; rate s were compared with C and protein loss rates over time. Additionally, experiments were designed to evaluate various artifacts involved in t he experimental use of radioisotopes, handling of biogenic debris, and the use of poisons. The release rates of C at 18-degrees-C exponentia lly decreased with time from 17.5% d-1 at 1 d to 2.7% d-1 at 6 d; thos e of protein slowed from 9.2% d-1 at 1 d to 2.0% d-1 at 6 d. Rates at 18-degrees-C were 2-4 times faster than rates at 4-degrees-C. Rate cha nges at both temperatures were much less pronounced from 6-25 d. Reten tion half-times (t(r1/2)s) of Ag, Am, Ce, Co and Pb in diatom debris w ere significantly greater than those of Cd, Se and Zn under the same c onditions; t(r1/2) values decreased inversely with temperature. The t( r1/2) values of C and protein were generally comparable to those of Cd , Se and Zn, whereas the ratios of the other metals to C and protein i ncreased significantly over time. Microbial activity very strongly enh anced Co scavenging onto decaying particles in the dark. The elemental loss rate data suggest that Cd, Se and Zn should generally follow the fate of organic C and protein in decomposing planktonic debris. These elements should be biologically recycled and have longer residence ti mes in surface waters than the other metals which are more particle-re active and which do not follow organic C and protein release.