Critical Load Concept to Set Restoration Goals for Liming Acidif ied Nor wegian Waters

Abstract

The concept of critical load is now widely used in the management of acidified waters. In southern Norway, acidification due to long‐range transported air pollutants is one of the most serious environmental problems, affecting an area of 80,000 km2. To preserve and restore biodiversity, Norwegian authorities have chosen liming as a temporary mitigation measure. Critical load estimates were used to estimate the material and financial needs for this large‐scale program. In 1995, more than 2000 localities ranging from small lakes to large salmon rivers were limed. Liming costs in 1996 were $18 million (U.S.). Critical load estimates also formed the basis for international negotiations on sulfur emission reductions, resulting in the second sulfur protocol for Europe and North America in 1994. The critical load estimates indicated that acidified areas in Norway would be reduced to 35,000 km2 after the year 2010, after the commitments of the sulfur protocols are met. By that time, estimated liming costs would be reduced by almost 40%. Lime treatment of River Tovdalselva, with a catchment area of 1885 km2, is probably the largest integrated liming project in the world. In 1990 the critical load was exceeded in 98% of the Tovdalselva catchment. After the year 2010 the exceeded area may be reduced to 44% and the liming cost by two‐thirds.