Effects of acidification on aquatic biota in Atlantic Canada

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ISSN： 1181-8700

Source： Environmental Reviews, Vol.19, Iss.1, 2011-12, pp. : 429-460

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Abstract

Acidification of surface waters is a high-profile environmental issue in Atlantic Canada. Despite a reduction of emissions of acid-precursors (particularly SO₂) by more than 50% in major regions in North America, there has not yet been a significant recovery of surface waters in the region, likely because of the impoverished acid-neutralizing capacity (ANC) of watersheds. Nevertheless, any detection of a biological recovery in the region requires knowledge of acidification threshold values for indicator species, so that they can be used in an appropriate bio-monitoring program. Our review of information on the effects of acidification on aquatic organisms in Atlantic Canada suggests that the greatest changes in phytoplankton occur over a pH range of 4.7 to 5.6, just beyond the interval (pH5.5 to 6.5) where bicarbonate (HCO3?), a key source of both ANC and inorganic carbon for photosynthesis, becomes rapidly depleted and then lost. Similarly, the pH threshold of 5.5 appears to be critical to sensitive macrophytes. The pH tolerance is highly variable among invertebrate taxa, but the median tolerable pH for most sensitive species is between 5.2 and 6.1. Sensitive fish species are affected at pH levels as high as 6.0-6.5, but tolerant ones may do well even at pH<5.0. Amphibian species are relatively tolerant, surviving even to pH3.5 to 4.0. Aquatic birds breed in the region at pH values greater than 5.5.