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The author compared the impact of toxic waste sites on three streams in South Carolina and Florida. In addition to the field evaluations of macroinvertebrate distribution (as determined by artificial leaf-pack collectors), a series of acute (4-day) and chronic (30-day) leaf-pack bioassays were carried out with polluted water and leaf-pack microcosms taken from the related study sites. The comparison of laboratory and field data was carried out over a one to two-year period at quarterly intervals. These experiments were designed to evaluate and verify the use of microcosms in predicting field impact and to test for possible seasonality in the laboratory-field relationship.
Leaf-pack data from the field indicated that there was no impact in a South Carolina stream (Myers Creek) because the toxic wastes never entered the surface water system. The four-day leaf-pack bioassay was useful in confirming the lack of adverse effects in the field. Field gradients of macroinvertebrates were evident in Hogtown Creek, Florida (from the low dissolved oxygen and high levels of phenolic derivatives), and in the Little Dry Creek/Dry Creek system, Florida (from the low pH and high lead and aluminum). The acute leaf-pack tests in the Hogtown Creek system did not predict the field impact as well as the chronic tests, whereas both forms of testing in the Little Dry Creek/Dry Creek system were effective in the prediction of field impact. In both systems, the presence of pollution-resistant species complicated the direct extrapolation of bioassay results to field conditions. There was considerable variation in the responses of individual species to the laboratory conditions; however, species richness was a relatively robust laboratory indicator of impact in both streams. Variables that had some influence on the ability to predict field impact using bioassay tests included local features of the stream system, the type of toxic waste, the duration of laboratory exposure to the toxic agents, and the community index used for the comparison. In some instances, the period of sampling was a factor in the laboratory-field relationship. These test results indicate that calibration of the macroinvertebrate microcosm with field data is necessary if such tests are to be used to predict field impact of toxic wastes. Such microcosms, properly used, can be effective for extrapolation of laboratory results to complex field conditions.
macroinvertebrates, microcosms, field verification, toxic wastes, bioassays, hazard evaluation
Professor and director, Center for Aquatic Research and Resource Management, Florida State University, Tallahassee, FL