Macroinvertebrate Assemblages in Shale-Draining Streams of North- Central Arkansas, USA

Natural and anthropogenic release of metals into surface waters and sediments may alter benthic community structure. To better understand macroinvertebrate communities in metal-impacted shale-draining streams in north-central Arkansas, sediment and macroinvertebrate samples were collected from sites on black shale-draining (BLS) and limestone- draining streams (LMS; used as a reference stream). The samples were collected during three sampling occasions targeting periods of stable flows between October 2003 and July 2005. Analyses of metals in water and sediment samples were done according to US EPA 200.8 and 6020 methodologies, respectively. Habitat surveys and macroinvertebrate community sampling, processing and taxonomy were done following US EPA’s rapid bioassessment protocols as well as methods outlined in Ohio Environmental Protection Agency. Concentrations of cadmium, copper, and nickel in BLS sediments were significantly (p < 0.05) higher than those of LMS samples. The concentrations of cadmium (range: 0.5 - 5.3 ppm), copper (2.2–64), and nickel (6.2–18) in the BLS sediments exceeded the Effect Range-Low values of NOAA’s sediment quality guidelines. Except for Chironomidae genera, all macroinvertebrate abundance and richness metrics were significantly lower in BLS than LMS sites (p < 0.05). The percent Ephemeroptera-Plecoptera-Trichoptera (EPT) was between two and seven times higher in LMS than BLS sites. The abundance and richness of metal-sensitive taxa (e.g. Heptageniidae and Chloroperlidae) were significantly lower in BLS samples than those of LMS. Negative correlations between sediment metal concentrations and macroinvertebrate richness metrics were also observed. The observed low macroinvertebrate abundance and taxa richness at BLS sites were attributed in part to elevated metal concentrations in sediments and water. Knowledge of the impacts of shale-derived metals on the spatial and temporal distribution of macroinvertebrate is vital in the management of watersheds underlain by black shales. Such information forms the basis upon which sound state and federal government land and water management and conservation policies are made.