BASE CATION DEPLETION AND POTENTIAL LONG-TERM ACIDIFICATION OF NORWEGIAN CATCHMENTS

Long-term monitoring data from Norwegian catchments show that since th e late 1970's, sulfate deposition and runoff sulfate concentrations ha ve declined significantly. However, water quality has not significantl y improved, because reductions in runoff sulfate have been matched by equal declines in calcium and magnesium concentrations. long-term decl ines in runoff Ca and Mg are most pronounced at catchments subject to highly acidic deposition; the observed rates of decline are quantitati vely consistent with depletion of exchangeable bases by accelerated le aching under high acid loading. Even though water quality has not reco vered, reductions in acid de position have been valuable because they have prevented significant acidification that would otherwise have occ urred under constant acid deposition. Ongoing depletion of exchangeabl e bases from these catchments implies that continued deposition reduct ions will be needed to avoid further acidification and that recovery f rom acidification will be slow.