FRESH-WATER LIMING

Operational liming of surface waters is part of Sweden and Norway's st rategy to counteract freshwater acidification caused by air pollutants . Smaller scale liming efforts are performed as research or experiment al programs in other countries. Yearly, approx. 300,000 tons of fine-g rained limestone (CaCO3) is spread in lakes and streams and on wetland s to mise the pH in surface water at a cost of approximately 40-50 mil lion $US. The chemical target is set by the biological goals and objec tives. A total of over 11,000 lakes and streams are treated on a conti nuing basis. Dose calculations consider pH, inorganic monomeric Al, di ssolved organic matter and the necessary buffering. Lake liming, limed osers at streams and terrestrial liming are used. A mix of different l iming techniques is often preferred to get an optimal result. The vast majority of changes are desirable and expected. Undesirable effects m ay appear and damaged wetlands are probably the most serious ones. Cos t-benefit analysis show that liming may be profitable for the society. Recovery of the systems can take up to 10-20 years. Liming will in th e long run restore the ecosystems but will not make them identical to what may be the original ones. In some cases, complementary measures, e.g. facilitation of recolonization, are necessary to enhance recovery . Reduced emissions of acidifying pollutants according to signed proto cols will decrease the need for liming, but still liming is needed for several decades in large regions to preserve biodiversity.