Inadequacy of size distributions of stream benthic diatoms for environmental monitoring

Abstract Benthic diatom assemblages respond to changes in water quality, and this response is evidenced by shifts in taxonomic composition. As a result, several taxon-based indices have been developed for monitoring purposes. Some authors have suggested that diatom body size might provide a simpler method for bioassessment than taxonomy-based approaches. Moreover, current knowledge of algal ecology suggests that the slopes and intercepts of density size distributions should vary with environmental characteristics. However, results from studies of the relationship between algal size and trophic variables including P have been mixed. Our objectives were to examine normalized density size distributions and richness size distributions of benthic diatoms in streams along a gradient of agricultural land use to determine whether the size distributions changed in relation to environmental variables. Benthic diatoms from 29 streams in eastern Canada were identified and average body size measurements were obtained ...