Acid deposition

Sensitivity of terrain to acidity

Graphic thumbnail: sensitivity of terrain to acidity

This graphic has two maps. The first is a map of Canada that uses seven colour codes to classify the sensitivity of terrain to acid in southern Canada, with the exception of the Prairies, according to the critical load index. It shows that most acid sensitive areas (defined as less than 300 on the critical load index) are in northwestern Boreal Shield, northeastern Boreal Plains, Hudson Plains, the southern part of the western Taiga Shield, and much of Nova Scotia and Newfoundland. Other areas of high sensitivity (300 to 400 on the critical load index) include the western half of the Boreal Shield in Quebec and the southern tip of the Boreal Cordillera. The remainder of the map shows critical load index levels of greater than 400, indicating non-sensitive terrain.

The second map uses three colour codes to show where the critical load was exceeded in the Boreal Shield in 2009. It was exceeded by more than 300 units in a large area in the southeast of the ecozone+. The perimeters of that area show exceedences to a lesser degree, of 0 to 300 units. A second smaller area of exceedence was found in the far west of the ecozone+ and along its western edge. Here, critical load was exceeded in scattered areas by 0 and 300 units, with a few small areas exceeding 300 units.

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Trends in sulphate levels and acidity in Boreal Shield lakes

Graphic thumbnail: trends in sulphate levels and acidity in Boreal Shield lakes

This graphic consists of two graphs with five lines each, showing the trends in sulphates and pH in five Boreal Shield lakes. Data for Clearwater and Rawson lakes are from 1973 to 2007 and data for Plastic, Batchawana, and Laflamme lakes are from 1982 to 2007. The first graph shows an overall decline in sulphate levels in all five lakes despite annual fluctuations. Clearwater Lake (near Sudbury) shows a steep decline, decreasing from close to 600 micro-equivalents per litre in 1973 to close to 200 micro-equivalents per litre in 2007. The four other lakes all show much slower declines of less than 100 micro-equivalents per litre for the time period.

The second line graph shows the fluctuating pH levels for each of these five lakes over the same time period. Clearwater Lake shows a substantial increase in pH, changing from just over 4.0 pH units in 1972 to approximately 6.3 pH units in 2007. The increase was steady until 1990 when it increased more rapidly until slowing down again in the early 2000s. The other lakes fluctuate annually and show no trend over the same time period.

An inset map shows the locations of these five lakes, spread along the southern border of the ecozone+.

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Impact of acidification on Atlantic salmon

Graphic thumbnail: impact of acidification on Atlantic salmon

This map of Nova Scotia shows the location and status of salmon rivers in southern, eastern, and western Nova Scotia in 1996. Fourteen runs, mostly located in the southeast part of the province, with a couple near Halifax, were extinct. Twenty rivers had only remnant populations and 15 experienced depletion of salmon runs in some tributaries.

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