Diatom reference communities in Québec (Canada) streams based on Kohonen self-organizing maps and multivariate analyses

Abstract

The identification of biological reference conditions specific to each type of water body is essential for the development of sound biological indicators and criteria. The purpose of the present study was to establish the reference conditions of each stream type sampled in southern Québec (Canada) using benthic diatoms and environmental variables characterizing streams and watersheds. First, stream reaches were classified as a function of their natural watershed and habitat characteristics. Second, diatom communities were classified based solely on taxa abundance data. Resulting groups were graphically presented on ordinations to interpret, a posteriori, the environmental gradients associated with diatom groups and to identify the diatom communities representing the reference conditions of each of the stream reach groups. A final classification based solely on diatom reference communities found pH and conductivity to be the main discriminating factors, regardless of ecoregion and stream type. Although a specific diatom reference community may be identified for each stream group, our results suggest that many of these communities exhibit strong similarities. Only two reference communities may therefore be used, one for circumneutral conditions and one for alkaline conditions. These reference communities represent the baseline for biocriteria development.