Decrease in acid deposition - Recovery in Norwegian waters

Concentrations of sulphate in precipitation in southern Norway have decreas ed by 50-60% from 1980-1999. This has caused a decrease in sulphate concent rations in lakes of 30-40% from 1986-1999. Nitrogen in precipitation has de creased slightly over the last 10-years. In lakewater there has also been a significant but slight decrease. Concentrations of non-marine base cations in precipitation have decreased by 40% from 1980-1999. In lakewater, non-m arine base cation concentrations have been at about the same level the last 10 years. This indicates that acid deposition has decreased sufficiently s uch that the pool of exchangeable base cations in the soil is now being rep lenished. The acidification situation in lakes in Norway has thus shown a c lear improvement over the last 8-10 years. pH, alkalinity and ANC (acid neu tralising capacity) have all increased. Concentrations of inorganic (toxic) aluminium species have decreased. The trends in H+ and Aln+ do not follow the relation expected if Aln+ concentrations were governed solely by a sing le solid phase of Al(OH)(3).