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Measuring the Biological Status of Freshwater Ecosystems: Emerging Challenges in the Derivation, Application, and Interpretation of Biological Indicators

Charles P. Hawkins

Western Center for Monitoring and Assessment of Freshwater Ecosystems, Department of Watershed Sciences, and the Ecology Center, Utah State University, Logan, UT

After decades of development within and across continents, the literature describes a remarkable array of biological indicators - each of which differs in what is measured, how raw biotic data are summarized, the error associated with predicting and estimating indicator values, their responsiveness to stressors, and hence, the inferences we draw regarding biological condition. Such differences among indicators present interesting challenges both for agencies that employ multiple indicators for regulatory purposes and for region-wide assessments in which indicator comparability across sites is a necessary requirement.

To address these challenges we must: identify indicators that more explicitly map to biological attributes of fundamental importance, identify indicators that are most ecologically appropriate for different spatial scales of observation, refine methods for improving the accuracy and precision with which we predict and estimate indicator values, and develop indicators that are truly diagnostic of the stressors affecting water bodies. Addressing these challenges will require that we: (1) carefully consider whether indicators should emphasize detection ability (responsiveness) or the measurement of those biological properties we understand to be ecologically important, (2) consider what types of measures are most meaningful at individual sites versus regions as a whole, (3) overcome the data quality constraints associated with our currently crude characterization of the biota present at individual sites, and (4) develop a more comprehensive understanding of both the ecological requirements of the taxa that inhabit freshwater ecosystems and hence their likely responses to stressors associated with watershed and waterway alterations.

Keywords: biological indicators, interpretation, refinement, future challenges

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