title: Assessing the recovery of lakes in southeastern Canada from the effects of acidic deposition.
abstract: Reductions in North American sulfur dioxide (SO2) emissions promoted expectations that aquatic ecosystems in southeastern Canada would soon recover from acidification. Only lakes located near smelters that have dramatically reduced emissions approach this expectation. Lakes in the Atlantic provinces, Quebec and Ontario affected only by long-range sources show a general decline in sulfate (SO4(2-)) concentrations, but with a relatively smaller compensating increase in pH or alkalinity. Several factors may contribute to the constrained (or most likely delayed) acidity response: declining base cation concentrations, drought-induced mobilization of SO4(2-), damaged internal alkalinity generation mechanisms, and perhaps increasing nitrate or organic anion levels. Monitoring to detect biological recovery in southeastern Canada is extremely limited, but where it occurs, there is little evidence of recovery outside of the Sudbury/Killarney area. Both the occurrence of Atlantic salmon in Nova Scotia rivers and the breeding success of Common Loons in Ontario lakes are in fact declining although factors beyond acidification also play a role. Chemical and biological models predict that much greater SO2 emission reductions than those presently required by legislation will be needed to promote widespread chemical and latterly, biological recovery. It may be unrealistic to expect that pre-industrial chemical and biological conditions can ever be reestablished in many lakes of southeastern Canada.
authors.affiliation: National Water Research Institute of Environment Canada. dean.jeffries@ec.gc.ca
authors.forename: Dean S
authors.initials: DS
authors.lastname: Jeffries
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clair
authors.forename: Suzanne
authors.initials: S
authors.lastname: Couture
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Dillon
authors.forename: Jacques
authors.initials: J
authors.lastname: Dupont
authors.forename: Wendel
authors.initials: W
authors.lastname: Keller
authors.forename: Donald K
authors.initials: DK
authors.lastname: McNicol
authors.forename: Michael A
authors.initials: MA
authors.lastname: Turner
authors.forename: Robert
authors.initials: R
authors.lastname: Vet
authors.forename: Russell
authors.initials: R
authors.lastname: Weeber
mesh_terms: D015258:Acid Rain; D000393:Air Pollutants / Q000009:adverse effects / Q000032:analysis*; D002170:Canada; D017753:Ecosystem; D004784:Environmental Monitoring; D006863:Hydrogen-Ion Concentration; D007221:Industry; D009566:Nitrates / Q000378:metabolism; D013458:Sulfur Dioxide / Q000009:adverse effects / Q000032:analysis*; D014867:Water / Q000737:chemistry; D014881:Water Supply
chemical_list: D015258:Acid Rain; D000393:Air Pollutants; D009566:Nitrates; D014867:Water; D013458:Sulfur Dioxide