| Summary: | The management of aquatic ecosystems is important to preserve the ecosystem services provided to humanity. The development of environmental assessment has allowed the management and therefore protection of these important resources. Reference Condition Approach (RCA) bioassessments using benthic macroinvertebrates as indicators are common tools that provide a means of determining impairment of stream sites by comparing exposed test sites to relatively unexposed reference sites. RCA predictive models are commonly developed at the scale of drainage basin, ecoregion, or political region (i.e. United Kingdom or Australian state), and test site assessment is restricted within the spatial boundaries of the model. If test site assessment can be applied outside the spatial scope of the model, insofar that the environmental characteristics are similar, it would reduce extensive sampling i.e. remote northern locations and time-consuming development of numerous models. The overall goal of my study was to assess whether a predictive model applied across a larger spatial extent, and therefore encompassing a greater area for test sites to be assessed, is as effective as models generally developed within smaller geographic regions such as within a basin or watershed. Benthic invertebrates and habitat data from three areas in Canada were examined: the Attawapiskat River basin in northern Ontario, the Fraser River basin in British Columbia and the Yukon River basin. The RCA predictive model method was used in this study that determines the relationships between benthic community groups and the environmental descriptors that explain them and the Benthic Assessment of Sediment (BEAST) assessment method to compare test sites with a physical similar group of reference sites. The performance of the bioassessment was assessed using a common set of simulated impact (“simpacted”) sites with known responses iv of taxa to disturbance. Models for each basin and a multi-basin model were compared on prediction performance, parsimony, and ...
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