Reversibility of acidification: fish responses in experiments at Risdalsheia

Abstract

The Rain-project started in 1984, with the purpose to study effects on and changes in water quality, after excluding acid rain. Based on water chemistry, the runoff from the clean rain catchment has developed in a "positive" direction, responding to decreased input of SO4 and NOx. Toxicity of the runoff from the catchments at the RAIN-project, was tested with 5 strains of brown trout. The chemical composition of runoff water from the clean site has proved to be more toxin than water from the untreated, neighbouring site. The higher toxicity levels after excluding acid rain is assumed to be caused by reduced calcium concentrations in the runoff, while the pH and aluminium levels still were toxin. There proved to be significant difference in tolerance among the five strains tested.