ACIDIFICATION IN NORWAY - LOSS OF FISH POPULATIONS AND THE 1000-LAKE SURVEY 1986

Several regional surveys have demonstrated that lakes and watersheds in widespread areas of southern Norway are affected by acidic precipitation. In autumn 1986, The Norwegian Institute for Water Research (NIVA) conducted the 1000-Lake Survey on behalf of the Norwegian State Pollution Control Authority (SFT). The greatest loss of freshwater fish populations is to be found in the countries of Telemark, East and West Agder and Rogaland. The damage correlates well with pH and the concentrations of calcium and labile aluminium in the lakes. The number of barren lakes in Sørlandet and southern Vestlandet has doubled since 1971-1975. The chemical changes are characterized by a decrease in calcium and sulphate and an increase in aluminium and nitrate. There has been little change in pH. The total land area affected by acidification damage has increased from33 000 km2 in 1974-1979 to 36 000 km2 in 1986. In 1986, over 18 000 km2 were almost totally damaged compared with 13 000 km2 in 1974-1979, an increase in the most affected area of nearly 40%. The greatest increase was registered in eastern Norway. Data from the 1000-Lake Survey indicated that 52% of the lakes in southern Norway were endangered. A 30% reduction in loadings of sulphur compounds would lead to the restoration of 28% of these lakes. A further reduction of 50% would ensure viable conditions for fish in 40% of the lakes, given a constant nitrate level in the lakes. The promising results from the RAIN project given optimism concerning the implementation of such prognoses. © 1990.