A Comparison of Urbanization Effects on Stream Benthic Macroinvertebrates and Water Chemistry in an Urban and an Urbanizing Basin in Southern Ontario, Canada

Benthic invertebrate communities were compared in several watersheds within an urban basin and an urbanizing basin in southern Ontario, Canada. The urban watersheds of the Lake Ontario basin and the urbanizing watersheds within the Lake Simcoe basin share similar geologies, soils, and climates, but differ in the stage of urban development within these two basins. Correspondence analysis showed that invertebrate populations formed distinct groups split between these two basins owing to intense urban development in the Lake Ontario watersheds versus the agricultural nature of the Lake Simcoe basin. Canonical correspondence analysis ordinations indicated that the major environmental gradients were related to urban land cover (imperviousness), chloride, nitrates and stream order factors. Urban land cover and chloride were most strongly associated with the first axis. The typical logarithmic relationship between urban land cover and benthos found in other studies was not evident in this study. Rather, 9 of the 12 metrics tested had significant linear relationships with urban land cover. The Hilsenhoff Family Biotic Index and percent Oligochaeta metrics showed the strongest positive linear relationships with urban land cover. Pollution sensitive groups (Ephemeroptera, Plecoptera, and Trichoptera) along with richness and diversity measures decreased with increasing urbanization.