PARENT SESSION
Symposium 8: Ecosystem response and recovery: Assessing the 1991 Canada-US Air Quality Agreement
Organized by: RA Haeuber, R Birnbaum, and K Timoffee
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 517 B, Level 5, Palais des congrès de Montréal
Assessment of predicted lake recovery from acidification in eastern Canada.
McNicol, Donald*,1, Jeffries, Dean2, Weeber, Russ1, Moran, Michael3, Wong, Isaac2, Vet, Robert3, Aherne, J4, Watmough, S4, Russell, R1, 1 Environment Canada, Ottawa, Ontario, Canada2 Environment Canada, Burlington, Ontario, Canada3 Environment Canada, Downsview, Ontario, Canada4 Trent University, Peterborough, Canada
ABSTRACT- An estimated 0.5 to 1.8 million km2 of eastern Canada continues to receive damaging levels of acid deposition. From 25% (New Brunswick) to 40% (Ontario) of recently sampled lakes had pH levels below 6, an important threshold for biological effects. The chemistry of many monitored lakes is responding to reductions in acidic deposition, but several factors are delaying or diminishing chemical improvements. Estimates of acidic deposition for sampled lakes were generated based on five acidifying emission scenarios: zero-anthropogenic emissions (Original), observed 1980/1984 (s1980), observed 1995/1996 (s1995), achievement of Canada-U.S. Air Quality Agreement targets and other existing and planned emission controls (s2020), and a hypothetical 25% reduction beyond s2020 (s2060). Predicted steady-state lake pH and acid neutralizing capacity (ANC) differed among scenarios and provinces. Predicted chemical recovery was generally small for the Atlantic provinces. Sampled lakes in Québec were predicted to improve in pH and ANC but only with significant further emission reductions (s2060). More substantial improvements were predicted for Ontario lakes, but many still had predicted pH or ANC below their original levels. Predictions for lakes in three secondary watersheds in Ontario illustrate regional differences in original and future lake pH and ANC values. The dynamic geochemical model (MAGIC) illustrated the temporal changes in water chemistry expected from emission reduction. Predicted biological recovery varied with species acid sensitivity and trophic relationships. The percent of lakes in New Brunswick, Québec and Ontario predicted to be suitable for minnows and other small fish increased with greater emission reductions. Emission reductions were associated with increases in predicted habitat suitability for certain acid-sensitive mayfly and gastropod species and with decreases for several acid-tolerant dragonfly larvae and true bugs (Hemiptera). Emission reductions were predicted to lead to habitat suitability declines for the insectivorous common goldeneye (Bucephala clangula) and increases for the piscivorous common loon (Gavia immer). Chemical and biological predictions will be discussed with regard to both sampled lakes and to the lake population of selected Ontario watersheds.
Key words: emissions, acidification, recovery, biodiversity