Impacts of Acid Atmospheric Deposition on Woodland Soils in the Netherlands: III. Aluminum Chemistry
1987
Mulder, J. | van Grinsven, J. J. M. | Breemen, N. van
Annual element budgets for three acidic oak-birch (Quercus robur L.-Betula pendula L.) woodland soils in the Netherlands indicate high inputs of atmospheric (NH₄)₂SO₄ (2.35–3.45 kmol NH₄ ha⁻¹ yr⁻¹). Nitrogen transformations lead to strong acid inputs of 3.0 to 7.5 kmolc ha⁻¹ yr⁻¹ in these soils, which are neutralized primarily by solubilization of Al in the surface 20-cm mineral layers (3–7 kmolc ha⁻¹yr⁻¹). We hypothesize that Al was relatively important in neutralizing strong acid inputs, due to the high acid loading and the low content of base cations. At the low pH (pH 3.27–4.26) dissolved Al in the mineral soil was mainly in aquo-Al³⁺ form. Highest Al concentrations (up to 4 molc m⁻³) were reached in summer and coincided with high NO⁻₃ concentrations. In winter and spring, the export of Al with drainage water peaked and solute concentrations decreased. All Al mobilized in the surface layers of soil A was retained below the 40-cm depth, probably due to cation exchange, since below this depth base saturation increased. In the deeper horizons of soils B and C, immobilization of Al was less, probably because base saturation was low. All subsoil solutions were undersaturated with respect to gibbsite and near equilibrium with jurbanite. Formation of jurbanite is unlikely, however, because mass balance calculations do not indicate net SO₄ retention.
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