Effects of stream size on taxa richness and other commonly used benthic bioassessment metrics

Michael H. Paller, Winona L. Specht, Susan A. Dyer

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Benthic macroinvertebrate samples were collected from natural substrates in disturbed and undisturbed South Carolina upper coastal plain streams to determine if taxa richness and other bioassessment metrics were significantly related to stream size as predicted by the River Continuum Concept (RCC). Linear, quadratic, and lognormal regression models indicated that stream width was positively related to total number of taxa; number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa; and total number of organisms. Linear regression showed that the expected number of taxa at undisturbed sites ranged from 35 in 2.0 m wide streams to 64 in 16.0 m streams. Comparable values were 8-20 for EPT and 109-261 for number of organisms. Stream width was inversely related to biotic index values indicating a decrease in average organism tolerance with increasing stream size. ANCOVA showed that the effects of stream size were similar for disturbed and undisturbed sites. Rank correlations and multidimensional scaling (MDS) showed that Lepidoptera and Trichoptera were more abundant in larger streams and Annelida in smaller streams. Stream size related changes in benthic macroinvertebrate community composition are often ignored in bioassessment protocols; however, failure to adjust metrics for stream size can lead to erroneous conclusions. Adjustments are possible by analyzing regression residuals stripped of stream size related variance, dividing the area beneath the maximum taxa richness line into equal size units for metric scoring, or scaling metrics based on predicted reference values.

Original languageEnglish (US)
Pages (from-to)309-316
Number of pages8
Issue number1
StatePublished - Sep 2006
Externally publishedYes


  • Bioassessment
  • EPT
  • Macroinvertebrates
  • River continuum concept
  • Species richness
  • Stream size

ASJC Scopus subject areas

  • Aquatic Science


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