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Acid Rain

Preliminary Indicator: Trends in lake acidity in southeastern Canada

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• Of 152 lakes monitored for acid rain effects in Ontario, Quebec, and the Atlantic Region between 1981 and 1997, 41% showed some improvement in acidity. Acidity levels were stable in 50% of the lakes and became worse in 9%.
• Seventy-three percent of the monitored lakes in Ontario are in the Sudbury region. Improvements in most of the lakes in the Sudbury area can be attributed to the substantial control of SO₂ emissions from local nickel smelters. Despite significant SO₂ controls in all of eastern Canada, the acidity of most lakes in the remainder of Ontario, and in Quebec and the Atlantic Region shows little change partly because of the continuing transboundary flow of acidifying emissions from the United States.
• Lake sulphate levels are indicators of the primary acidifying agent (sulphuric acid) in acid rain. Sulphate levels are declining in most lakes in Ontario, Quebec, and the Atlantic Region.
• Lake sulphate levels respond to a reduction in SO₂ emissions. A time lag of many years is possible before this translates into widespread regional improvements in lake pH or alkalinity. There is a further time lag before these improvements are likely to result in changes to populations of fish and other biota.

Notes:
  i) For acidity: Increasing pH or alkalinity implies an "improving" condition, decreasing pH or alkalinity implies a "worse" condition, no trend means "stable".
 ii) For sulphate: Decreasing levels imply "improving", increasing levels imply "worse", no trend means "stable".
iii) Number of Lakes: Atlantic Region, 63; Quebec, 37; Ontario, 52.
iv) Atlantic Region refers only to the provinces of Nova Scotia and Newfoundland.
 v) Most of the data sets spanned the period from 1981 to 1996–97. However, some data sets began in 1983.

Sources:
Atlantic Region: T.A. Clair, Environment Canada. Quebec: A. Kemp, Environment Canada. Northwestern Ontario: M.P. Stainton, Fisheries and Oceans Canada. Algoma: D.S. Jeffries, National Water Research Institute. Sudbury: W. Keller, Ontario Ministry of Environment. Muskoka/Haliburton: P.J. Dillon, Ontario Ministry of Environment.

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