Effects of stream size on taxa richness and other commonly used benthic bioassessment metrics |
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Authors: | Michael H Paller Winona L Specht Susan A Dyer |
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Institution: | (1) Environmental Analysis Section, Savannah River National Laboratory, Savannah River Site, Aiken, South Carolina 29808, USA;(2) Soil and Ground Closure Projects, Westinghouse Savannah River Company, Savannah River Site, Aiken, South Carolina 29808, USA |
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Abstract: | 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.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users. |
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Keywords: | macroinvertebrates stream size river continuum concept bioassessment species richness EPT |
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