LAUSR

Effects of moderate-to-severe sediment contamination may be readily discernable in both sediment toxicity bioassays and benthic community assessments. However, the impact may be less obvious under conditions of relatively mild contamination and significant variation of natural environmental variables. This study evaluated sediment toxicity and benthic community impacts for a shallow eutrophic lake system with relatively low levels of sediment metal contamination. We evaluated selected sediment physical and chemical properties, as well as benthic community structure, for 50 sites along a sediment Pb contamination gradient in the lake. We tested the toxicity of sediment from 20 of the sites, using a standardized 42-days sediment bioassay with Hyalella azteca survival, reproduction, and growth endpoints. Using principal component and correlation analyses we found negative relationships for both Pb and Cu, between sediment metal concentrations and the diversity and abundance of benthic macroinvertebrates. Taxa known to be metal-sensitive (e.g., Hyalella sp. and Physa sp.) were less abundant at sites with relatively higher Pb and Cu concentrations. However, amphipod performance in the chronic toxicity test was not related to sediment Pb or Cu concentrations (but was influenced by sediment organic content). Our results demonstrate that an assessment of community-level effects may be warranted even when sediment metal concentrations are too low to elicit detectable toxic effects in standardized laboratory tests.