An Evaluation of Rapid Bioassessment Protocols for Stream Benthic Invertebrates in Southern Ontario, Canada

In this study, we sampled stream benthos using rapid bioassessment methods (i.e., D-nets, coarse taxonomy) from sites in and around Toronto, Ontario that represented a range of stream characteristics (e.g., drainage areas). The protocols were developed by or adapted from: (1) Toronto and Region Conservation Authority, (2) Ontario Ministry of Natural Resources, (3) Ontario Benthos Biomonitoring Network/Ministry of the Environment, and (4) Canadian Aquatic Biomonitoring Network/ Environment Canada. Summary indices (Hilsenhoff's modified Biotic Index [HBI]; percent of fauna as Ephemeroptera, Plecoptera, and Trichoptera [% EPT]; number of taxa [S]; and Shannon's Diversity Index [H']) calculated from the resulting data were used to evaluate differences between protocols in a series of analyses including analysis of variance and variance components analysis. The study found that sampling method was an unimportant source of variation in summary index values relative to other factors such as the stream or year sampled. The largest percent variance amongst stream or year factors (main and interactions) was at least three times greater than the corresponding method related percent variances. The results of this study suggest that these four bioassessment methods are interchangeable within the context of large geographic scales or for the detection of major impacts. In cases where impacts to the benthic community are subtle, protocols should include one or more of discrete habitat sampling, replication, and lower taxonomic resolution. The data and findings here may help agencies integrate different sampling protocols into their biomonitoring and assessment programs.