Norwegian lakes show widespread recovery from acidification; results from national surveys of lakewater chemistry 1986-1997

摘要

Surveys of 485 lakes in Norway conducted in 1986 and againin 1995 reveal widespread chemical recovery from acidification. Sulphate concentrations inlakes have decreased by 40% in acidified areas in southern Norway. This decrease has beencompensated about 25% by decreases in concentrations of base cations and of 75% byincreased Acid Neutralising Capacity (ANC). The increased ANC in turn reflects lowerconcentrations of acidic cations Aluminum (ALn+) and Hydrogen (H+).A sub-set of 78 of the 485 lakes sampled yearly between 1986 and 1997 shows that, at firstmost of the decrease in non-marine sulphate (SO₄*) was compensated by adecrease in base cations, such that ANC remained unchanged. Then as SO₄* continued to decrease, the concentrations of non- marine calcium and magnesium ((Ca+Mg)*)levelled out.Consequently, ANC increased, and H+ and Aln+ started to decrease. Ineastern Norway, this shift occurred in 1989–90, and came slightly later in southern andwestern Norway. Similar shifts in trends in about 1991–92 can also be seen in thenon-acidified areas in central and northern Norway. This shift in trends is not aspronounced in western Norway, perhaps because of the confounding influence of sea-saltepisodes on water chemistry. This is the first documented national-scale recovery fromacidification due to reduced acid deposition. Future climate warming and potentiallyincreased N-leaching can counteract the positive trends in recovery from acidification.