Effects of Season, Habitat, and an Impoundment on Twenty-Five Benthic Community Measures used to Assess Water Quality

Abstract

Aquatic macroinvertebrates were sampled at 8 sites in 3 high quality trout streams in central Wisconsin to determine effects of season, habitat, and an impoundment on the variability and reliability of 25 commonly used benthic community measures. Monthly samples were collected for one year from six riffle and two snag habitat sites, except when ice and snow conditions prevented it. Values for the Biotic and Family Biotic Index (BI and FBI), four EphemeropteraPlecoptera- Trichoptera measures (EPT), Species and Generic Richness (SR and GR), Diversity Index (DIV), and 16 Trophic Function Measures (TFM) were determined. Significant differences (p<0.05) occurred between fall and summer values for BI, FBI, three EPT measures, and seven TFM and between spring and fall values for FBI, EPT, and three TFM. Significant differences occurred among all measures from snag and riffle samples in the same stream. Water quality classifications based on BI and FBI values usually indicated poorer water quality at snags than at riffles in the same stream. BI, FBI, DIV, one EPT measure, and two TFM had significantly different mean annual values between two riffles in the same stream. These results suggest that the use of benthic community measures should be restricted to specific seasons and habitats to increase their reliability as indicators of stream water quality. BI, FBI, one EPT measure, and five TFM had significantly different mean annual values between the upstream and below-dam sites, and BI, FBI, DIV, two EPT measures, and four TFM had significantly different mean annual values between the downstream and below-dam sites. Water quality classifications based on BI and FBI values usually indicated poorer water quality below the dam than upstream or downstream. Season, habitat, and the impoundment had little effect on measure variability. BI, FBI, DIV, SR, GR, two EPT richness measures, and three TFM had relatively low variability (coefficients of variation= 8.5-16.7%) and appear to be more reliable than EPT enumerations and other TFM.