Environmental Impact Prediction and Assessment: the Southern Indian Lake Experience

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Abstract
The impoundment of Southern Indian Lake (SIL) and diversion from the lake of the Churchill River in northern Manitoba, Canada, were the subjects of two independent environmental impact statements. Subsequently, a case study measured change in the limnological and biological characteristics of the lake after development. Comparison of pre- and post-impoundment observations allows an assessment of the predictive capability that was applied to the lake by the preimpact statements. Predictions related to the physical environment, e.g. increased shoreline erosion, littoral sedimentation, higher turbidity, and decreased light penetration and visibility, were qualitatively correct; however, an unpredicted decrease in water temperature also occurred. Increased phosphorus availability and light limitation of primary production were also correctly forecasted in a qualitative manner. These aspects will be quantitatively predictable in future reservoirs because of studies at SIL and elsewhere. Biological responses above the primary trophic level were mostly not predicted or predicted incorrectly. Unpredicted changes that were especially significant to the fishery were rapid declines in the quantity and quality of whitefish (Coregonus clupeaformis) catch, increases in mercury concentrations in fish, and the need for extensive compensation programs to keep the fishery economically viable. Testable hypotheses to explain all unpredicted events have been formulated but require experimental verification. The paradigm of reservoir ecosystem development that is present in the literature requires reformulation if future environmental impact analyses of reservoirs are to be improved.

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