Changes in the chemistry of lakes near Subury,Ontario following reductions of SO2 emissions

Emissions of SO₂ in the Sudbury area declined from an estimated average of 1.41 × 106 tonne yr^?1 in 1973–78 to 0.68 × 10⁶ tonne yr^?1 in 1979–85. As a result, SO₄ concentrations of lakes in the area have decreased, and the pH of each of the acidic lakes that was studied has increased. Aluminum, Cu, Ni and Zn concentrations have also decreased; however, the latter three metals have probably declined because of reductions in emissions of metals from the smelters rather than because of the pH changes in the lakes.