Structural and functional changes in the macroinvertebrate community of a fly ash receiving stream were investigated during the final year of fly ash basin operation and for 10 months after fly ash discharges to the stream were terminated. Minimal changes were observed in the benthic community until the basin reached 77% of capacity, at which time the number of macroinvertebrate taxa, density of organisms, diversity, and relative abundance of Ephemeroptera all declined sharply. Ephemeroptera (mayflies) exhibited the greatest sensitivity to the fly ash effluent, while the beetle, Psephenus herricki (Coleoptera) was very resistant to the effects of fly ash. Recovery responses of the macroinvertebrate community were observed one month after fly ash discharges to the stream ended, while full recovery required 10 months. Based on the results of the field study, the toxicity of fly ash constituents (fly ash particulates, pH excursions, and heavy metals) was examined in three species of aquatic insects: Stenonema pudicum (Ephemeroptera), Hydropsyche slossonae (Trichoptera), and Psephenus herricki. Fly ash particulates were not acutely toxic to the three species at concentrations of 4000 mg/l. Stenonema pudicum was consistently the most sensitive species to acidic and alkaline pH extremes and heavy metals (Cd, Cr, Cu, Zn, and a metal mixture), while Psephenus herricki was consistently the most resistant species tested. Alkaline pH extremes and elevated heavy metal concentrations are believed to be responsible for the observed changes in the macroinvertebrate community of the receiving stream during the final two months of basin operation, while elevated heavy metal concentrations were responsible for earlier perturbation of the stream community. / Ph. D.

Research estimated toxicity of refuse-derived fuel fly ash (RDF-FA) on two earthworms species, Lumbricus terrestris and Eisenia foetida. Specific objectives were to: (1) Compare their 14-day LC50s under light and dark conditions; (2) separate toxicity due to osmotic, pH and physical factors from that of heavy metal contaminants; (3) compare relative differences of artificial soil and commercial soil as exposure media for evaluating toxicity to earthworms. The 14-d LC50s for L. terrestris in dark and light were 57.0 and 48.34 % RDF-FA, and 59.25 and 41.00 % RDF-FA for E. foetida using artificial soil. All of the toxicity resulted from heavy metals within the RDF-FA. Using L. terrestris, the LC50s for artificial soil and commercial soil were 52.30 and 64.34%.