Not all areas of Canada are affected equally by acid rain.This is because areas differ in their ability to offset or neutralize acidity. This is largely determined by the type and rate of weathering of the soils and bedrock in the region.A region’s underlying bedrock (the geologic deposit from which a soil is derived by weathering) is the most important factor on how sensitive an area will be to acid rain. Alkaline substances, such as calcium, magnesium and potassium (known as “base cations”), are found in the earth’s bedrock and soil.
In essence, when an acid and a base combine, they cancel each other out, producing a neutral substance. When the rain is only mildly acidic, there are enough alkaline substances to balance the acidity and neutralize the effects on the soil and water. However, when the rain is highly acidic, these acid-buffering substances can become depleted. There may not be enough of them to continually offset the acid effect of the rain. When nature can no longer buffer the effect, the balance is lost. This is what has been slowly happening for the past 100 years in the natural environment due to acid rain. The areas most affected by acid rain are those with shallow soil cover on slowly weathering bedrock (since beneficial alkaline substances are released as the bedrock is weathered by incoming rain).
For example, igneous bedrock (e.g., the granite bedrock of the Canadian Shield that covers almost half of Canada) has a very low alkaline content and, therefore, can’t buffer the effects of acid rain. On the other hand, regions that are formed on limestone or sedimentary bedrock (e.g., southern Ontario and parts of western Canada), which contain high levels of calcium, can tolerate fairly high acidic deposits over long periods of time. Limestone is very alkaline, and so it can maintain an acceptable balance despite increased acidity.