The Open Environmental & Biological Monitoring Journal, 2008, 1, 33-42 33 1875-0400/08 2008 Bentham Open Open Access Macroinvertebrate Assemblages in Shale-Draining Streams of North- Central Arkansas, USA George M. Ogendi 1, * , Robyn E. Hannigan 1 and Jerry L. Farris 2 1 Department of Chemistry and Program of Environmental Sciences, Arkansas State University, P.O. Box 419, State University, AR 72467 and 2 Department of Biology, Arkansas State University, P.O. Box 847, State University, AR 72467, USA Abstract: 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 lime- stone-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 be- tween two and seven times higher in LMS than BLS sites. The abundance and richness of metal-sensitive taxa (e.g. Hep- tageniidae and Chloroperlidae) were significantly lower in BLS samples than those of LMS. Negative correlations be- tween sediment metal concentrations and macroinvertebrate richness metrics were also observed. The observed low mac- roinvertebrate abundance and taxa richness at BLS sites were attributed in part to elevated metal concentrations in sedi- ments and water. Knowledge of the impacts of shale-derived metals on the spatial and temporal distribution of macroin- vertebrate 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. Key Words: Black shales, weathering, metals, streams, macroinvertebrates, macroinvertebrate abundance and richness metrics. INTRODUCTION Evidence from both field and laboratory studies indicate that metal contamination in streams may alter the composi- tion and structure of macroinvertebrate communities [1-6]. Low total abundance and taxa richness of metal-sensitive macroinvertebrate taxa such as Plecoptera and Trichoptera have been noted in streams characterized by elevated metal levels [2]. Low abundance of metal-intolerant Ephemerop- terans (e.g. heptageniid mayflies) is common in streams con- taining elevated metal concentrations [2, 5, 7]. Other studies have documented high abundance of metal-tolerant chiro- nomids and oligochaetes in metal-contaminated waters and sediments [4, 5, 8-10]. The observed low abundance of metal-sensitive macroinvertebrate taxa have been attributed to increased mortality, diminished growth, and low recruit- ment [2, 5]. Some metal-sensitive macroinvertebrate taxa are less impacted by elevated metal concentrations. This in- cludes those taxa become metal-tolerant [11] after prolonged *Address correspondence to this author at the Department of Chemistry and Program of Environmental Sciences, Arkansas State University, P.O. Box 419, State University, AR 72467, USA; Tel: 870-972-3086 Ext. 2399; Fax: 870-972-3089; E-mail: george1971ke@yahoo.com exposure to elevated metal levels and those that maintain steady populations through wind drift from sites that are un- affected by metals [4, 12]. Over the last few decades, macroinvertebrates have been used in assessing impacts of metals from active and aban- doned mining sites, thus providing insights on the health of stream ecosystems [2, 5-8]. However, little is known of mac- roinvertebrate assemblages in streams that are contain ele- vated metal levels such as those draining metal-enriched rock outcrops. Several studies have shown that physical and chemical weathering of black shales releases potentially toxic metals into the adjacent soils, surface waters and sedi- ments [13-18]. Weathering of black shales may be acceler- ated by anthropogenic activities in the watershed. Recent studies have shown that water and sediments in streams draining the Mississippian Fayetteville Shale of north-central Arkansas contain elevated metal concentrations that may, under certain conditions, be detrimental to macroinverte- brates and other stream biota [15, 17]. Whereas the bulk of the metals in water and sediments result from natural geo- logic processes, the influence of human activities cannot be ignored. The constant release of potentially toxic metals into shale streams warrants continuous monitoring so as to pro-