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Diversity indexes, particularly those based on information theory, have been widely promoted as the best method for assessing the impact of effluents on macroinvertebrate communities. Despite their superiority, neither the Shannon-Weaver index (SWI) nor the Brillouin index (BI) is universally applicable. The SWI is preferred where effluents are selective (for example, organics) and BI preferred where effluents are nonselective (for example, heavy metals). Despite their simplicity, it should be remembered that diversity indexes supplement, not replace, community analyses based on species richness and population densities. Covariance analyses and more tightly defined stratified sampling programs are discussed as ways of improving the accuracy of density estimates.
Impact prediction depends on models predicting changes in species richness and population densities. A mechanistic model predicting changes in species richness as a function of oxygen supply and demand is offered as a step in this direction. Despite its accuracy in undisturbed streams, the applicability of the model to organic and thermal pollution awaits testing. Implications of the model for impact prediction are discussed.
water pollution, water quality, impact assessment, impact prediction, diversity, species richness, streams, ecology, effluents, aquatic organisms
Assistant professor of biology, University of Michigan—Dearborn, Dearborn, Mich.