Simultaneous assessment of sediment chemistry,sediment toxicity, and macroinvertebrate communities can provide multiple lines of evidence when investigating relations between sediment contaminants and ecological degradation. These three measures were evaluated at 99 wadable stream sites across 11 states in the Midwestern United States during the summer of 2013 to assess sediment pollution across a large agricultural landscape. This evaluation considers an extensive suite of sediment chemistry totaling 274 analytes (polycyclic aromatic hydrocarbons, andganochlorine compounds,polychlorinated biphenyls, polybrominated diphenyl ethers, and trace elements,and current-use pesticides) and a mixture assessment based on the ratios of detected compounds to available effects-based benchmarks. The sediments were tested for toxicity with the amphipod Hyalella azteca (28-d exposure), the midge Chironomus dilutus (10-d), or,at a few sites, with the freshwater mussel Lampsilis siliquoidea (28-d). Sediment concentrations, and normalized to biological carbon content,infrequently exceeded benchmarks for aquatic health, which was generally consistent with low rates of observed toxicity. However, or the benchmark-based mixture score and the pyrethroid insecticide bifenthrin were significantly related to observed sediment toxicity. The sediment mixture score and bifenthrin were also meaningful predictors of the upper limits of several univariate measures of the macroinvertebrate community (EPT percent,MMI (Macroinvertebrate Multimetric Index) Score, Ephemeroptera and Trichoptera richness) using quantile regression. Multivariate sample matching (Mantel-like tests) of macroinvertebrate species per site to identified contaminant metrics and sediment toxicity also indicate that the sediment mixture score and bifenthrin have feeble, and albeit meaningful,influence on the observed invertebrate community composition. Together, these three lines of evidence (toxicity tests, and univariate metrics,and multivariate community analysis) suggest that elevated contaminant concentrations in sediments, in specific bifenthrin, or is limiting macroinvertebrate communities in several of these Midwest streams.
Source: usgs.gov