MEIOFAUNAL BIOTURBATION EFFECTS ON THE PARTITIONING OF SEDIMENT-ASSOCIATED CADMIUM

Two experiments were conducted using laboratory cultured meiofauna to measure bioturbation effects on cadmium partitioning. The benthic harp acticoid copepod, Amphiascus tenuiremis cf. Mielke, and the foraminife ran, Ammonia beccarii cf. Linne' served as bioturbators. The first exp eriment utilized single and combined species treatments which were com pared to controls having no fauna. All treatments and controls used se diment spiked with Cd at the concentration at which 5% mortality occur s in the copepods (LC5). Cadmium concentrations were measured in the o verlying water, pore water, and sediment after 96 h to see if bioturba tion altered the partitioning of cadmium. The second experiment employ ed the same design as the first except that the number of organisms us ed was tripled to simulate reported field densities. Results from the first experiment revealed significantly higher amounts of Cd in the po re waters of all treatments relative to the controls. There were also between treatment differences showing that copepod-only treatments res ulted in the highest concentration of pore water Cd. With the second e xperiment, it was assumed that this bioturbation effect would be even greater due to the increased number of organisms used. However, this w as not seen. Treatment pore water Cd concentrations of Experiment 2 we re not significantly higher than like treatments from Experiment 1. Bo th experiments demonstrated that meiofaunal bioturbation has a signifi cant effect on the partitioning of Cd in muddy sediments.