INSIDE: Damaging deluge Smelting and refining of sulfur-bearing metal ores and the combustion of fossil fuels for transportation, power generation, and heating produce sulfur dioxide and nitrogen oxide.

Situated where an evergreen forest overlies the Canadian Shield, the Boreal Shield is the largest of Canada’s terrestrial ecozones. This natural region — popularly known as “shield country” — extends 3,800 kilometres from Saskatchewan to Newfoundland and Labrador. It covers 1.8 million square kilometres and encompasses almost 20 percent of Canada’s landmass; its myriad rivers and lakes account for 22 percent of Canada’s freshwater surface area. The Boreal Shield’s rich supply of minerals and lumber plays a major role in fueling the economy of the “heartland” of southern Ontario and Quebec. Its bare rock, thin soils, and muskeg have restricted development to resource exploitation. Some major communities — Chicoutimi-Jonquière, Sudbury, Elliot Lake, and Thunder Bay — have successfully diversified their economic base, while other one-industry centres have experienced significant declines in population and primary-resource activity. Although less than 10 percent of Canadians reside here, the Boreal Shield’s beauty attracts outdoor enthusiasts from urban centres in the south.