The effects of acid rainfall and heavy metal particulates on a boreal Forest ecosystem near the sudbury smelting region of Canada

Abstract

Sulphur dioxide and particulate pollution have been occurring over a wide area in the Sudbury region, Ontario, as a result of massive smelting operations. In excess of 3Z million short tons of SO₂ were released into the atmosphere in the area in 1972, and this pollutant is now discharged through a 1250-foot smokestack. The particulate contribution is an additional complicating and phytotoxic factor. For example, in 1971, 192 tons of nickel, 145 tons of copper, 1130 tons of iron and 4.5 tons of cobalt per 28 days from two of the smelters were released as airborne pollutants (Hutchinson and Whitby, 1974). The natural vegetation of the area is a mixed deciduous boreal forest, with white pine (Pinus strobus), jack pine (Pinus banksiana), red maple (Acer rubrum), red oak (Quercus rubra), etc. as dominant trees. This forest, which previously surrounded the mining town of Sudbury, has been devastated over the past 50 yr, especially by the SO₂ emissions and the increased acidity of rainfall and soils. An area in excess of 100 mi² is now almost devoid of vegetation and damage to the forest vegetation is visible over an area of approximately 1800 mil. The increased stack heights to dilute local pollution problems have spread the problem more widely. The pH of rainfall sampled up to 12 mi east of the smallest smelter in 1970 was less than 4.3 and that within 2 mi of the stacks was frequently of less than pH 3.0. Soil erosion has occurred on a large scale as a consequence of loss of vegetation. Metal accumulation in the soils has also been a complicating and probably highly persistent phenomenon. Concentrations of nickel in excess of 3000 ppm and copper of 2000 ppm in surface soils occur widely. The increased acidity of these soils has increased metal mobility and solubility, presenting phytotoxic problems. The effects on the soil chemistry, especially of organic composition have been profound. They involve an increased metal binding capacity of these soils, and very high levels of sulphur in the purified Tulvic acid′ fraction itself. Indeed, the evidence is suggestive of the incorporation of sulphonic groups into the changed extracts. Such profound and damaging changes may be merely a consequence of the extreme conditions experienced at Sudbury or they may be a harbinger of things to come in many potentially podsolic soils in areas of increasing acidity of rainfall.