Browsing by Author "McCormick, Paul V."

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    Evaluating potential groundwater contamination from contaminated soils
    Pratt, James R.; McCormick, Paul V.; Pontasch, K. W.; Cairns, John Jr. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1987)
    Contamination of soils at toxic and hazardous waste sites can adversely affect groundwater and surface water. Water soluble materials can move in soil by leaching and percolation and by runoff. This project evaluated the toxicity of leachable toxicants from seven soils, five of which were obtained from designated toxic or hazardous waste sites. Acidified, dechlorinated tap water was used to extract toxic materials from surface soils. Extracts were used as complex mixtures in acute toxicity tests using Daphnia and in chronic effect tests using microcosms. Three classes of effects were observed. Some leachates (including control soils) showed no toxicity. Some soil leachates had moderate acute toxicity (50-80% diluted leachate) and no chronic toxicity. Very toxic soils showed both acute and chronic toxicity at < 3% leachate. Toxicological evaluations of contaminants in waste site soils can provide information not available from chemical analyses and may be useful in verifying the effectiveness of cleanup effort.
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    Patterns of microbial community development in isolated aquatic systems
    McCormick, Paul V. (Virginia Polytechnic Institute and State University, 1986)
    The purpose of this research was to compare the process of microbial community development in isolated aquatic systems to the MacArthur-Wilson equilibrium theory of island biogeography and suggest alternative models for the observed patterns. Water-filled plastic containers were used as aquatic islands to investigate the colonization dynamics of protozoan, algal and microinvertebrate taxa. Polyurethane foam (PF) artificial substrates were used as sampling devices in these systems. Distance from another aquatic system was found to have a significant effect colonization in these systems. Exclusion of macroscopic organisms, however, did not strongly affect the process of microbial community development in these systems. The results of short-term (36 day) and long-term (170 day) experiments suggest that no protracted species equilibrium is achieved in these systems; an initial asymptotic increase in species richness was followed by large oscillations in the number of species. There was no correlation between rates of species colonization and the number of species present. Rates of species extinction, however, increased with increasing species number. The estimated rate of species colonization was a non-monotonic function of time, increasing during the early stages of colonization and decreasing thereafter. These results, coupled with an analysis of temporal changes in species composition suggest that microbial community development in isolated systems is a deterministic process which may be best explained by an interactive model of species succession.