Use of Diatoms and Macroinvertebrates as Bioindicators of Water Quality in Southern Ontario Rivers

Abstract

The effectiveness of diatoms and macroinvertebrates as indicators of environmental conditions in lotic systems was compared in a regional assessment. Benthic samples were collected during summer 2000 from 35 Provincial Water Quality Monitoring river stations in the Grand, Credit, Maitland and Upper Thames watersheds in southern Ontario. Patterns of diatom and macroinvertebrate taxon distributions in relation to environmental variables were determined using canonical correspondence analysis (CCA). Total nitrate, phosphate, conductivity and alkalinity were significant in explaining diatom data, while alkalinity, total nitrate, ammonium and total Kjeldahl nitrogen were significant in explaining invertebrate data. The eigenvalues of the first two CCA axes were significant (p < 0.05) for both diatoms and invertebrates, while the invertebrate analysis explained more taxonomic variation (19% vs. 12%). Regression and calibration models were developed for total nitrate. The correlation between taxon-inferred and observed values was higher for diatoms than invertebrates in the analysis (0.70 vs. 0.59), however, cross-validation with bootstrapping indicated that apparent coefficients may be inflated. Biotic indices were also calculated. The composite invertebrate metric scores gave a slightly closer representation of water quality conditions than the diatom trophic index, but, biotic indices were not as effective as CCA in describing sites. Overall, the invertebrate and diatom communities were similar in their abilities to predict water quality.