A Review and Analysis of Some Methods Used to Measure Functional Aspects of Periphyton

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Abstract
Historically, assessments of water quality using periphytic communities have centered around indexes of structure such as biomass estimates, diversity indices, cluster analyses, and species abundances and distributions. However, perturbation of a community's structural attributes may not be concomitant with functional changes, and it follows that protection of community structural integrity would not signify protection of ecosystem function. A series of model streams provided semicontrolled experimental conditions for study of nontaxonomic attributes of periphytic community structure and function (photosynthesis) in response to a variety of perturbants. Over all of the model stream experiments, measured functional values were statistically less variable (P = 0.05) than measured structural values. No significant reduction in variability of structural or functional measurements was found for the treated streams relative to untreated or reference streams. A unified effort incorporating both structural and functional measurements should yield information adequate for accurate evaluation of impacts of perturbants on periphytic communities and aquatic ecosystems.