1983. Evidence of acidification sf some Nova Scotian rivers and its impact on Atlantic salmon, Salmo snlar. Can. J. Fish. Aquat. Sci. 40: 462-473.River pH's in Nova Scotia are closely reIated 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 HCOi concentrations and increases in AIWC and SOT. On average, 73% of the increase in acid is attributabie to increased SOT. Changes in Na', K9, Ca'+. and Mg" concentrations were not significant. In rivers presently at mean annual pH's c4.7, the Atlantic salmon (S~lrno s a k r ) 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 1854, 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. WATT, W. D., $1. B. SCOTT, AND W. J. WHITE. 1983. Evidence of acidification of some Nova Scotian rivers and its impact on Atlantic salmon, Snlrno solar. Can. 5. Fish. Aquat. Sci. 44): 462-473. En Pdouvelle-kcosse, le pH des rivieres est en ktroite relation avec la geologic. et les variations saisonnihes le sorat avec le dkbit des rivikres. Dans les regions gt5ologiques plus sensibaes (granite et r o c k s mktamorphiques). le pH des rivikres a baisse de faqon significative au cours des 27 dernikres annkes et cela 5 un taux moyen de 0.017 unit& pH/annCe. 11 s'est produit en m6me temps un dCclin de concentration de HCOi et un aceroissement de Al"' et SO:. En moyenne, 73 % de I'augmentation de l'acide est attribuable a l'augmentation de SO:. Drarant la mCme @riode, il ne s'est produit aucun ehangement significatif des concentrations de Na', K', Ca'* et Mg". Les populations de saumsns ataantiques (Saltno salar) ont disparu des rivi5res dont le pH annuel moyen est infbrieur B 4,7 et sont pr6sumkes Cteintes.Les rivikres B pH de 4,7-5,0 montrent un dCclin des prises sportives de 2,8 % par annie patir de 1954 et de faibies densites de juvkniles. Les rivieres B pH srm@rieur a 5,0 snt en gCn6ral des densitCs de saumoneaux normales et ne montrent abscune tendance significative des prises sportives.
In 1981, the Department of Fisheries and Oceans carried out an experimental neutralization of an acidified lake in Nova Scotia. The purpose of this experiment was to determine whether lake liming could be used as a technique to control the pH of Atlantic salmon habitat downstream from the lake and to learn the proportion of lime which would be dissolved, the effects of liming on water chemistry, and the duration of these effects relative to the retention time of water in the lake. The experiment was carried out on Sandy Lake in the Sackville River system near the town of Bedford, Nova Scotia. Sandy Lake is 74 ha in area, 5,100,000 m3 in volume, and its retention time is 0.34 years. Its water chemistry was normal for lakes in the Halifax area and its pH was between 4.5 and 5.0 before lime was added. In July and August 1981, 135,000 kg of CaCO3 were mixed with water in a mixing tank mounted on a boat and then spread over the lake surface. The pH of the epilimnion rose quickly from below 5.0 almost to 7.0 and that of the hypolimnion rose approximately to 6.0. Following fall overturn, the whole‐lake pH fell quickly almost to its pre‐liming value. Fluctuations of pH 3 km downstream from the lake were equal to those in the lake. The effects of liming on pH had disappeared by the end of February 1982. On a few occasions in the fall and winter following liming, a shallow stratum of exceptionally acid water overlay the mass of limed water in the lake. The usefulness of lakes as reservoirs of neutralized water may be reduced by incomplete mixing of acidic inflows with the lake water and consequent low pH of the outflow. By the end of 1982, approximately 60% of the lime added to the lake had been detected in the water column. The remainder is presumed to have been immobilized on the lake bottom. Concentrations of Al, Mn, Cu, and Zn were significantly lower following liming but that of Fe was higher. Although it is feasible to add lime to headwater lakes to regulate fluctuations in the pH of rivers and to maintain the pH at levels favourable to Atlantic salmon; in Nova Scotia where lakes are small and their rates of flushing are rapid, lime must be added at frequent intervals.
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