Sensitivity of bedrock to acid precipitation: modification by glacial processes

Abstract
In Canada, the simple relationship of soils to underlying bedrock has been distorted by glaciers which have transported debris from one type of bedrock onto areas where the rock may have a different composition. For example, on the Canadian Shield north of Lake Superior, continental glaciers have spread a sheet of glacial deposits, rich in calcium carbonate, onto granitoid rocks over an area extending hundreds of kilometres west and south of the limestone basin of Hudson Bay. These limestone-rich glacial deposits have imparted significant buffering capacity to terrain that, in the absence of glaciation, would have produced quartz-rich so ils with high sensitivity to acid precipitation. Similar situations exist elsewhere in southeastern Canada. Acid precipitation, by lowering the pH of glacial soils or of surf ace waters, also may mobilize potentially noxious chemical elements that under natural conditions are stable in the soil or in lakes or streams.

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