Evidence of Acidification of Some Nova Scotian Rivers and Its Impact on Atlantic Salmon, Salmo solar

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Abstract
River pH in Nova Scotia are closely related to geology, and seasonal pH variation is well correlated with river discharge rates. In the geologically sensitive areas (granite and metamorphic rocks), river pH have fallen significantly over the past 27 yr at an apparent average rate of 0.017 pH units/yr [acid rain]. Concomitant with this decrease are a decline in HCO3- concentrations and increases in Al3+ and SO4=. On average, 73% of the increase in acid is attributable to increased SO4=. Changes in Na+, K+, Ca2+ and Mg2+ concentrations were not significant. In rivers presently at mean annual pH < 4.7, the Atlantic salmon (S. salar) runs have disappeared and are presumed extinct. Rivers in the pH range 4.7-5.0 show a decline in salmon angling returns of 2.8%/yr, begining about 1954, and low densities of juvenile salmon. Rivers presently of pH > 5.0 generally have normal juvenile densities and show no significant trend in angling returns.