Responses of a macroinvertebrate community from a pristine, southern British Columbia, Canada, stream to metals in experimental mesocosms

Metal contamination is one of the most widespread impacts on surface waters . Experimental flumes receiving water and aquatic invertebrates from an und isturbed, forested stream were used to determine the impact of metals in a low-conductivity stream. The experimental flumes were exposed to a gradient of doses maintaining a constant ratio of metals (1995: Cu, Zn, Mn, and Pb, 1996: Cu and Zn) fur 6 d. Benthos and emigration were sampled from each of the 10 troughs. The overall densities of benthos declined, but not signifi cantly, as the dose of metals increased. On the basis of the slopes of the concentration-response curve, Baetis, Ameletus, and Paraleptophlebia were t he most sensitive taxa present. Other taxa (e.g., Nemouridae and Oligochaet a) were mildly affected by high metal concentrations. Chironomidae showed n o significant decrease in densities with increasing dose. Chironomids made up >80% of the benthos and is the primary reason for no significant dose ef fect on overall densities. No treatment effect was observed on either algal standing crop or bacterial respiration rates. The invertebrate genera most affected by exposure to metals in this study were also absent or rare in n earby urban streams with high metal concentrations.