Assessment of habitat impairments impacting the aquatic resources of Lake Ontario

A habitat classification system was used to describe aquatic habitat and evaluate habitat degradation in Lake Ontario. Primary consideration was given to physical loss or disruption of habitat availability; because habitat availability was treated as a functional entity, disruptions or stresses caused by chemical or biological sources were included. Data on biological, chemical, and physical anthropogenic changes were scattered, patchy, and disjointed. Therefore, the Delphi technique was used to evaluate the degree of functional habitat impairment for 29 habitats. The criteria for the impairments were the severity of the ecological impact (shift in trophic transfer efficiency) and its permanence (short > decades > permanent). The amounts of functional degradation were averaged by habitat categories (N = 88) for each habitat and multiplied by the estimated areal proportion of that habitat in the ecosystem. We estimated that during 1970-1990, Lake Ontario's ecosystem health was degraded by 58%. Impairments were caused almost equally by anthropogenic stresses from biological (loss of indigenous and introduction of exotic species), chemical (persistent toxins), and physical (dredge-fill, damming, and water-level regulations) sources. Our finding is consistent with a late 1980s study that used lake trout (Salvelinus namaycush) as an indicator of ecosystem health.