Jeffries D S, Brydges T G, Dillon P J, Keller W
Environment Canada, National Water Research Institute, P.O. Box 5050, Burlington, ON, Canada L7R 4A6.
Environ Monit Assess. 2003 Oct-Nov;88(1-3):3-19. doi: 10.1023/a:1025563400336.
Aquatic acidification by deposition of airborne pollutants emerged as an environmental issue in southeastern Canada during the 1970s. Drawing information from the extensive research and monitoring programs, a sequence of issue assessments demonstrated the necessity of reducing the anthropogenic emissions of acidifying pollutants, particularly sulphur dioxide (SO2). The 1991 Canada-U.S. Air Quality Agreement (AQA) was negotiated to reduce North American SO2 emissions by approximately 40% relative to 1980 levels by 2010, and at present, both countries have reduced emissions beyond their AQA commitment. In response to reduced SO2 emissions, atmospheric deposition of sulphate (SO4(2-)) and SO4(2-) concentrations in many lakes have declined, particularly in south-central Ontario and southern Québec. Sulphate deposition still exceeds aquatic critical loads throughout southeastern Canada however. Increasing pH or alkalinity (commonly deemed 'recovery') has been observed in only some lakes. Several biogeochemical factors have intervened to modify the lake chemistry response to reduced SO4(2-) input, notably release of stored SO4(2-) from wetlands following periods of drought and reduction in the export of base cations from terrestrial soils. Three examples from Ontario are presented to illustrate these responses. Significant increases in pH and alkalinity have been observed in many lakes in the Sudbury area of Ontario due to the large reductions in local SO2 emissions; 'early-stage' biological recovery is evident in these lakes. An integrated assessment model predicts that AQA emission reductions will not be sufficient to promote widespread chemical or biological recovery of Canadian lakes. Monitoring and modeling are mutually supporting assessment activities and both must continue.
20世纪70年代，空气中污染物的沉降导致的水体酸化成为加拿大东南部的一个环境问题。从广泛的研究和监测项目中获取信息后，一系列问题评估表明有必要减少酸化污染物的人为排放，特别是二氧化硫（SO₂）。1991年，加拿大和美国协商达成了《空气质量协议》（AQA），目标是到2010年将北美地区的SO₂排放量相对于1980年的水平减少约40%，目前，两国的排放量减少幅度已超过其在AQA中的承诺。随着SO₂排放量的减少，许多湖泊中硫酸盐（SO₄²⁻）的大气沉降和SO₄²⁻浓度都有所下降，特别是在安大略省中南部和魁北克省南部。然而，加拿大东南部各地的硫酸盐沉降仍超过水体的临界负荷。仅在一些湖泊中观察到pH值或碱度增加（通常称为“恢复”）。有几个生物地球化学因素介入，改变了湖泊化学对减少的SO₄²⁻输入的响应，特别是干旱期后湿地中储存的SO₄²⁻的释放以及陆地土壤中碱性阳离子输出的减少。本文列举了安大略省的三个例子来说明这些响应。由于当地SO₂排放量大幅减少，安大略省萨德伯里地区的许多湖泊的pH值和碱度显著增加；这些湖泊中已明显出现“早期”生物恢复。一个综合评估模型预测，AQA规定的减排量不足以促进加拿大湖泊广泛的化学或生物恢复。监测和建模是相互支持的评估活动，两者都必须继续。
