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Threats to Sources of Drinking Water and Aquatic Ecosystem Health in Canada, by Environment Canada – 2001

Environment Canada. 2001.  Threats to Sources of Drinking Water and Aquatic Ecosystem Health in Canada.   National Water Research Institute, Burlington, Ontario.  NWRI Scientific Assessment Report Series No. 1.  72p.  Page 69 – 15. Impacts of Dams/Diversions and Climate Change;  T.D. Prowse,1 J.M. Buttle,2 P.J. Dillon, 2 M.C. English, 3 P. Marsh, 1 J.P. Smol4 and F.J. Wrona1; 1Environment Canada, National Water Research Institute, Saskatoon, SK; 2Trent University, Peterborough, ON; 3Wilfrid Laurier University, Waterloo, ON; 4Queen’s University, Kingston, ON.

Below is an excerpt:

“Most of our current knowledge of the impacts of water quantity changes on water quality is based on studies of the effects of Canada’s more than 600 dams and 60 large interbasin diversions, which makes the nation the world leader in water diversion (Day and Quinn 1992).  Most Canadian dams store water during peak flow periods and release flow to generate power during winter, low-flow periods.

Such changes to water quantity also modify various water quality parameters within the reservoir and downstream, the effects decreasing with distance from the impoundment.  Major examples include:

  • thermal stratification within the reservoir and modification of downstream water temperatures
  • eutrophication;
  • promotion of anoxic conditions in hypolimnetic water and related changes in metal concentrations in outflow;
  • increased methylation of mercury;
  • sediment retention;
  • associated changes in TDS, turbidity and nutrients in the reservoir and discharged water;
  • increased erosion/deposition of downstream sediments and associated contaminants.

For impoundments used for drinking water, intra-storage processes also have serious implications for the quality of drinking water.”