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 decomposing diatom cells were determined using gamma-emitting radiotracers; rates were compared with C and protein loss rates over time. Additionally, experiments were designed to evaluate various artifacts involved in the experimental use of radioisotopes, handling of biogenic debris, and the use of poisons. The release rates of C at 18°C exponentially decreased with time from 17.5% d−1 at 1 d to 2.7% d−1 at 6 d; those of protein slowed from 9.2% d−1 at 1 d to 2.0% d−1 at 6 d. Rates at 18°C were 2–4 times faster than rates at 4°C. Rate changes at both temperatures were much less pronounced from 6–25 d. Retention half-times (tr1/2s) of Ag, Am, Ce, Co and Pb in diatom debris were significantly greater than those of Cd, Se and Zn under the same conditions; tr1/2 values decreased inversely with temperature. The tr1/2 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 increased significantly over time. Microbial activity very strongly enhanced 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 times in surface waters than the other metals which are more particle-reactive and which do not follow organic C and protein release.
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Document Type: Research Article
Publication date: 1993-05-01
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