Evaluating Stream Bioassessment Protocols using Data from the Clark Fork’s Ecoregion
  Wease Bollman, Rhithron Biological Associates, 1845 South 12th West, Missoula, MT

  ABSTRACT: A proposed method for the evaluation of macroinvertebrate bioassessment protocols is described in this study. The Montana Department of Environmental Quality (Montana DEQ) uses a modification of US EPA’s Rapid Bioassessment Protocols for stream assessment and monitoring. These protocols use a battery of macroinvertebrate community descriptors, or metrics, as indicators of biotic health; the metrics are based upon tenets of ecological theory and field observations and remained largely untested for sensitivity to the effects of human activities.

            To evaluate the metric battery in current use, 93 stream sites were sampled in the Montana Valley and Foothill Prairies ecoregion (which includes the river valleys and foothills of the Clark Fork Basin) . These sites were classified as highly impacted by human activities, moderately impacted and less impacted, based upon visual assessment of habitat and watershed information. Twenty-two metrics, including those comprising the state’s protocol, were tested. Eight metrics were able to distinguish less impaired sites from highly impaired sites. Seven of these impact-sensitive metrics were highly correlated with habitat assessment parameters. Anthropogenic impacts explained over one-third of the variability in six metrics. Based on these results, a battery of seven metrics was assembled. This metric battery proved to be more sensitive to impact, better related to habitat variables, and more consistent in assigning impairment categories than the battery used by Montana DEQ.

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