Improvements in water quality and aquatic ecosystems due to reduction in sulphur deposition in Norway

A program for monitoring acidification in Norway was developed in 1980. The program included water chemistry, fish and invertebrates. The monitoring h ave been performed in areas with strong as well as low acidification. Infor mation about the status of the fauna is regularly obtained from sites cover ing both affected and unaffected areas. Tolerance limits for different spec ies have been established and used for the evaluation of changes in acidifi cation since the early eighties. A significant improvement in water chemist ry was recorded in accordance with a 45 to 70% reduction in sulphur deposit ion. The invertebrate monitoring shows recovery of sensitive species, and w atersheds with earlier low damage have probably returned to an unaffected s tatus. In the most acidified areas also significant improvements are noted, especially during the last ten years. However, acidic episodes connected w ith sea-salt deposition and spring snowmelt are found to confound the recov ery process in these naturally low buffered systems.