Linking ecological impact to metal concentrations and speciation: A microcosm experiment using a salt marsh meiofaunal community

Microcosm experiments addressed the impact of a mixture of Cu, Cr, Cd, Pb, and Hg at three concentrations after 36 h, 12 d, and 30 d on a meiofauna-do minated salt marsh community. In addition to analyzing effects on meiofauna l abundances, the study quantified the sediment metal concentrations of all five metals and pore-water concentrations, speciation, and ligand complexa tion of Cu. Abundances of deposit feeders such as the polychaete Streblospi o benedicti, gastropods, and bivalves were impacted at lower metal concentr ations than the mainly algal-feeding copepods, ostracods, and nematodes. We suggest that this might be due to bulk ingestion of metal-contaminated sed iments resulting in relatively higher metal exposure in the deposit feeders than in the other, nondeposit feeding taxa. Copepod and ostracod abundance s decreased only in the highest metal treatment, where levels of inorganic Cu ([Cu ']) in pore waters were similar to levels associated with both acut e and subacute toxicity in published in vivo toxicity studies of marine cop epods. The higher metal treatments yielded disproportionately higher pore-w ater [Cu] compared with sediment [Cu], suggesting saturation of sediment-as sociated ligands with increased additions of Cu. Similarly, the higher meta l treatments appeared to reach saturation of the organic Cu ligands, with t he excess pore-water [Cu] present in the more toxic, inorganic species of C u. Acid-volatile sulfide (AVS) concentrations at sediment horizons inhabite d by meiofauna were low and AVS was not considered a significant metal liga nd at these depths. Since meiofauna are predominantly associated with oxic surface sediments, it is doubtful that AVS is a major factor controlling av ailability of free metal for exposure to these taxa.