| Abstract: | Theoretical constructs, such as the river continuum concept, predict that the composition of benthic fauna in rivers will
be different from that of headwater streams. There exists a need to modify, for use on larger rivers, the bioassessment techniques
commonly used on small streams. Using aquatic macroinvertebrates and the “reference condition” approach, we developed and
tested a multimetric index for use on the rivers of Idaho. Reference sites were selected to represent the best current conditions
(i.e., least impacted) among Idaho rivers. The index performed well in distinguishing reference sites from sites displaying
some form of anthropogenic impairment. Individual metrics used in the index included: number of EPT taxa, total number of
taxa, percent dominant taxon, percent Elmidae, and percent predators. The index we developed for Idaho rivers was essentially
a modification of a framework designed for small streams, suggesting that techniques, including data analysis, currently used
for streams can be adapted for use on larger rivers. Adapting these methods for use in rivers is primarily a matter of (1)
selecting metrics relevant to the rivers of interest; (2) expanding the field sampling to encompass the greater habitat area
and, potentially, heterogeneity of rivers; and (3) selecting an appropriate form of data analysis. The approach we describe
here should be applicable to geographic regions other than Idaho. |
