Effect of sediment-associated copper on ecological structure and function of aquatic microcosms

Abstract

Fate and effect of sediment-associated copper (Cu) on the structure and function of aquatic communities were studied in aquatic microcosms that were constructed from naturally derived water and sediment. Sediment was spiked with nominal Cu concentrations of 0, 10, 100, or 1 000 mg/kg dry sediment. Copper partitioning between sediment particles, pore water, and overlying water was followed in an 8-wk long experiment. Most of the added Cu was bound to sediment particles. There was no evidence that the structural or functional measures were affected in microcosms containing the nominal concentration of 10 mg Cu/kg sediment. In 100 mg/kg microcosms, with Cu concentration of about 0.5 mg/l of overlying water, chlorophyll a content and respiration significantly decreased compared to the control. Failure to detect significant impact on other structural and functional attributes probably resulted from the high variability of the nontaxonomic attributes and the displacement of species sensitive to Cu by the tolerant species. In microcosms containing the nominal concentration of 1 000 mg Cu/kg (about 20 mg Cu/l of overlying water), the community showed a significant decrease in production, respiration, respiration/biomass ratio, ATP, and chlorophyll a; assimilation ratio and autotrophic index were significantly higher than in the control. Results of this study may be useful in predicting the impact of similar toxic stress on natural ecosystems.