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

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<jats:p> River pH's 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's have fallen significantly over the past 27 yr at an apparent average rate of 0.017 pH units/year. Concomitant with this decrease are a decline in [Formula: see text] concentrations and increases in Al<jats:sup>+++</jats:sup> and [Formula: see text]. On average, 73% of the increase in acid is attributable to increased [Formula: see text]. Changes in Na<jats:sup>+</jats:sup>, K<jats:sup>+</jats:sup>, Ca<jats:sup>++</jats:sup>, and Mg<jats:sup>++</jats:sup> concentrations were not significant. In rivers presently at mean annual pH's < 4.7, the Atlantic salmon (Salmo 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, beginning 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. </jats:p>

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