Comparison of models predicting invertebrate assemblages for biomonitoringin the Fraser River catchment, British Columbia

A multivariate, predictive model based on the reference-condition approach is described for the Fraser River catchment in British Columbia. Benthic in vertebrate assemblages and environmental descriptors were measured at more than 200 sites from 1994 to 1996, including 219 reference sites. Reference sites were classified into groups representing similar invertebrate assembl ages. Five such classifications were produced, using three taxonomic levels (family, genus, and species) and species and family multimetrics. For each of the classifications, discriminant function analysis was used, with envi ronmental descriptors, to develop a predictive model for the reference site s. These models predicted from 43.8% (species) to 61.6% (family) of the ref erence sites to the correct benthic group. Each model was used to assess de viation from reference condition for 21 test sites exposed to either agricu lture, logging, or mining. The models were examined with regard to their se nsitivity, robustness, usability, temporal variability, predictive performa nce, and model certainty. The family and family-metric models were ranked b est, followed by the species-metric, genus, and species models. The family- level model is recommended for assessment purposes; its overall performance was slightly superior to the family-metric model and it avoids an extra st ep in calculation of the metrics. However, the species-level model is recom mended for conservation or biodiversity issues.