The concept of critical load is now widely used in the management of acidif
ied waters. In southern Norway, acidification due to long-range transported
air pollutants is one of the most serious environmental problems, affectin
g an area of 80,000 km(2). 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 t
his large-scale program. In 1995, more than 2000 localities ranging from sm
all lakes to large salmon rivers were limed. Liming costs in 1996 were $18
million (U.S.). Critical load estimates also formed the basis for internati
onal negotiations on sulfur emission reductions, resulting in the second su
lfur protocol for Europe and North America in 1994. The critical load estim
ates indicated that acidified areas in Norway would be reduced to 35,000 km
(2) 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%. L
ime treatment of River Tovdalselva, with a catchment area of 1885 km(2), is
probably the largest integrated liming project in the world. In 1990 the c
ritical load was exceeded in 98% of the Tovdalselva catchment. After the ye
ar 2010 the exceeded area may be reduced to 44% and the liming cost by two-
thirds.