Bulk deposition, throughfall, stemflow, litterfall, soil solution (B horizon), above-ground biomass increment and soil were sampled and the annual fluxes of water, H+, Na, K, Ca, Mg, Al, Mn, NH4, NO3, SO4 and Cl were quantified in adjointing stands of Picea abies, Fagus sylvatica and Betula pendula at two sites in southern Sweden. The total atmospheric deposition of H+ to the spruce canopies was two to eight times the deposition to beech or birch canopies. The corresponding figures for NH4, NO3 and SO4 deposition were 1.5 to 3.0. Soil budgets showed a net loss of base cations from all soils, especially from the spruce soils. Proton budgets showed the calculated total proton load to the spruce stands to be two to five times the load to the beech or birch stands. The total proton load was mainly attributable to atmospheric H+ input (50 to 83%) and base-cation incorporation into the above-ground biomass (26 to 43%). Much of the acidity was exported in the form of Al ions to deeper soil layers and Al buffering was the major buffer mechanism. Compared to beech and birch, spruce greatly promoted soil acidification. The results indicate that unless acid and nitrogen deposition is much reduced, soil acidification and mineral nutrient loss are likely to continue in a majority of south Swedish forest soils with low weathering rates, particularly in the spruce forest soils, because of the much greater acidifying influence of spruce than of deciduous trees.
Abstract