AN ABSTRACT OF
WEATHERING OF BLACK SHALES AND THEIR IMPACTS ON SURFACE WATER AND SEDIMENT QUALITY, AND AQUATIC ORGANISMS

Weathering of black shales leads to elevated dissolved metals in water and sediments. Despite increasing interest in black shale research, there are limited data on the quality of water and sediments of streams draining black shale geologic units. The main goal of this study was to assess the quality of water and sediments of shale-draining streams with respect to metal contamination, and the associated metal impacts on aquatic organisms. Four streams in North-Central Arkansas, USA, were selected for study, three (Trace, Begley, and Cove creeks) of which drain the Mississippian Fayetteville Shale. A fourth nearby stream (Mill Creek) that flows over a geologically different Mississippian Pitkin Limestone bedrock was selected as a reference. To realize the stated objective, water, sediment, and macroinvertebrate samples were collected from the study sites between June 2003 and July 2005. Metal concentrations in water and sediments were determined by the ICP-MS, DRC II. Whole sediment toxicity tests using Chironomus tentans as well as chronic toxicity tests using Ceriodaphnia dubia and Pimephales promelas were conducted to determine the toxicity of the water and sediments to the test organisms. Concentrations of dissolved Cd, Cu, Hg, Ni, Pb, Se, and Zn in water from shale-draining streams (Trace, Begley, and Cove creeks) were significantly higher (p ≤ 0.05) than those of the limestone-draining stream. The dissolved metal concentrations also approached and /or exceeded US EPA’s surface water quality criteria with regard to these metals. Concentrations of dissolved metals were significantly higher during stromflow conditions compared with those of baseflow conditions. Sediments from shale-draining streams had considerably higher total metal and simultaneously extracted metals concentrations compared with those from the limestone-draining stream. Water hardness, acid volatile sulfide, dissolved organic carbon, conductivity, organic carbon and clay contents in water and sediments were significantly high if the bedrock of the catchment area consisted of Fayetteville Shale than if it consisted of Pitkin Limestone. The survival, growth, and reproduction of C. dubia, P. promelas, and C. tentans in water and sediments collected from shale-draining streams were significantly lower compared with those of the limestone stream. Except for Chironomids, all macroinvertebrate abundance and richness metrics were significantly lower in shale-draining streams than those of limestone-draining stream. Abundance and taxa richness of metal-sensitive Heptageniids and Chloroperlids in shale-draining streams were significantly lower than those of the limestone stream. Strong negative and significant correlations were observed between sediment metal concentrations and macroinvertebrate taxa richness, and also between sediment metal concentrations and the survival and growth of C. tentans. The survival, growth, and reproduction of C. dubia and P. promelas were also strongly and significantly correlated with concentrations of dissolved metals in water. The observed low macroinvertebrate abundance, taxa richness and the low survival, growth, and reproduction in shale-draining stream water and sediments for C. dubia, P. promelas and C. tentans were attributed to the elevated metal contamination in the streams.

You may contact Dr. Ogendi for more information on his dissertation and current research via email: george1971ke@yahoo.com