Ecological Aspects of AIr Pollution From an Iron-Sintering Plant at Wawa, Ontario

At Wawa, in northern Ontario, vegetation has been damaged severely by sulphur dioxide pollution from an iron-sintering plant. Damage is mainly restricted to a narrow strip northeast from the sinter plant, since southwest winds are strongly predominant. It is traceable from the air for at least 20 miles in this direction and is estimated as severe within 11 miles and very severe within 5 miles. Within about 10 miles NE. from the sinter plant ground flora variety declines markedly, from about 20–40 species per 40 square meter quadrat beyond this distance to 0–1 species within 2 miles of the pollution source. At the same time sulphate in lake and pond waters increases greatly, from normal levels of about 0.2–0.3 milliequivalents per liter to more than 0.5 meq/l. within 11 miles NE. and up to 2 meq/l. within 2 miles NE. from the sinter plant. Waters within about 5 miles NE. are strongly acid (pH 3.2–3.8), but are not low in calcium. Soluble sulphate in the surface soil rises sharply within about 4 miles NE. from the pollution source, where, also, soil erosion is very pronounced, though traceable farther out.The phanerogams most tolerant of air pollution are Polygonum cilinode and Sambucus pubens, which are infrequent in the normal forest vegetation. In quadrat studies along a northeast transect, seedlings of pinus strobus were not observed within 30 miles from the sinter plant, while those of Picea glauca, P. mariana, and Populus tremuloides were not recorded within 15 miles.