The operational definition of the “critical” load for wet SO4 deposition is that which does not increase the regional percent of lakes having pH≤6 for the portion of the population that historically had pH>6. Reviews of the effects of acidic deposition on aquatic biota show that the pH=6 threshold used to determine the critical load is sufficient to protect most organisms. It is inappropriate to specify a single critical load for the whole of eastern Canada due to variability in terrain sensitivity. The Atlantic provinces and easterr Quebec generally have very low critical loads (<8 kg. ha−1.yr−1). The terrain characteristics of this area dictate a critical load very close to background deposition. Lakes in southwestern Quebec and Ontario have critical loads of <8 to >20 kg.ha−1.yr−1 reflecting the wide range in terrain sensitivities that exist in each province.
Assessment of the Effect of Acidic Deposition on Canadian Lakes: Determination of Critical Loads for Sulphate Deposition
D. S. Jeffries, D. C. L. Lam; Assessment of the Effect of Acidic Deposition on Canadian Lakes: Determination of Critical Loads for Sulphate Deposition. Water Sci Technol 1 August 1993; 28 (3-5): 183–187. doi: https://doi.org/10.2166/wst.1993.0418
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