Monitoring the results of Canada/U.S.A acid rain control programs: some lake responses

摘要: Aquatic acidification by deposition of airborne pollutants emerged as an environmental issue in southeastern Canada during the 1970s. Drawing information from extensive research and monitoring programs, a sequence assessments demonstrated necessity reducing anthropogenic emissions acidifying pollutants, particularly sulphur dioxide (SO2). The 1991 Canada-U.S. Air Quality Agreement (AQA) was negotiated to reduce North American SO2 ∼40% relative 1980 levels 2010, at present, both countries have reduced beyond their AQA commitment. In response emissions, atmospheric sulphate (SO4 2−) SO4 2− concentrations many lakes declined, south-central Ontario southern Quebec. Sulphate still exceeds aquatic critical loads throughout however. Increasing pH or alkalinity (commonly deemed ‘recovery’) has been observed only some lakes. Several biogeochemical factors intervened modify lake chemistry input, notably release stored wetlands following periods drought reduction export base cations terrestrial soils. Three examples are presented illustrate these responses. Significant increases Sudbury area due large reductions local emissions; ‘early-stage’ biological recovery is evident An integrated assessment model predicts that emission will not be sufficient promote widespread chemical Canadian Monitoring modeling mutually supporting activities must continue.