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Research Document - 2000/057

A review of the effectiveness and feasibility of alternate liming techniques to mitigate for acid rain effects in Nova Scotia

By White, W.

Abstract

This paper is a summary of some techniques that may be applicable to liming acid rivers in Nova Scotia. It emphasises the preservation of Atlantic salmon habitat. Acid rain has eliminated salmon entirely from some rivers in Nova Scotia and reduced salmon production in many others. Controls on atmospheric emissions have produced less improvement than expected in the pH of Nova Scotia's rivers. As an interim measure, alkaline substances (lime) can be added to acidified surface waters to raise their pH. Liming is costly and is justified only where equivalent benefits to fish can be produced. A pH of 5.3 is necessary to protect salmon in Nova Scotia during the incubation period through to first feeding. Salmon parr and smolt require a minimum pH of 5.0. Liming adds calcium to natural waters and this may confer additional benefits on fish besides raising the pH of their habitat. Concentrations of toxic metals do not increase in limed waters. Limestone is usually the best neutralising substance owing to its relatively low cost and safety. Other substances are available but these are more expensive and may be dangerous to personnel handling them and to the fish.

Once liming has been carried out, the higher pH can only be maintained by frequent or continual liming. This paper describes several methods of applying lime to lakes and rivers. The factors that affect efficiency of dissolution are discussed. Methods are described for calculating the required lime dose for each method of liming. The relative costs, efficiency and reliability of different liming techniques are compared.

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