ACIDIFICATION TRENDS, LIMING STRATEGY AND EFFECTS OF LIMING FOR VIKEDALSELVA, A NORWEGIAN SALMON RIVER

The River Vikedalselva located on the southwestern part of Norway is monitored to detect acidification trends and liming effects as part of national monitoring programmes. The acidification of the river ha caused repeated fish kills of smolts and presmolts of Atlantic salmon (Salmon salar L.) and sea trout (Salmo trutta L.). The river showed significant negative trends for pH, non-marine sulphate and non-marine calcium and positive trends for nitrate and aluminium during the period 1980 to 1991. Changes in these parameters were most pronounced during the period 1985-1990. Because of the fish kills a liming programme for the river was initiated in 1987. Continuous liming was controlled by pH measured 700 m downstream the liming point in a feed-back system. Long term dissolution of previously sedimented limestone powder may thus be accounted for in the dose calculation. pH was maintained at remarkably constant values. This liming strategy may ensure optimal water quality for salmonids at low costs. “Complete abstract not presented.”