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An Experiment on the Feasibility of Rehabilitating Acidified Atlantic Salmon Habitat in Nova Scotia by the Addition of Lime
Author(s) -
White W. J.,
Watt W. D.,
Scott C. D.
Publication year - 1984
Publication title -
fisheries
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 79
eISSN - 1548-8446
pISSN - 0363-2415
DOI - 10.1577/1548-8446(1984)009<0025:aeotfo>2.0.co;2
Subject(s) - hypolimnion , lime , epilimnion , nova scotia , environmental science , hydrology (agriculture) , fishery , oceanography , ecology , geology , nutrient , eutrophication , biology , paleontology , geotechnical engineering
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 m 3 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 CaCO 3 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.