Influence of taxonomic determination level on several community indices

The aim of the present study was to test the possible influence of different taxonomic determination levels on several commonly used indices. Ephemeroptera, Plecoptera and Trichoptera communities of five acidified and three reference headwater streams were sampled 11 times during one year, providing quantitative faunistic lists. Richness, four diversity indices and two similarity indices were compared when calculated from species, genus and family determination levels. The results showed that high taxonomic level determinations lead to underestimation of all indices excepted for Jaccard which was overestimated. Underestimation was generally higher for communities of reference streams than for impacted streams. Consequently, determinations to family level make the interpretation of metric values very hazardous, especially when indices are used to assess both water quality and macroinvertebrate community changes.