Acid deposition and ion leaching from a podzolic soil under hardwood forest

Abstract

The contribution of atmospheric acids to cation leaching from a podzolic soil under mature maple-birch forest in central Ontario was examined during 1983. The movement of base cations was associated largely with NO₃ ⁻, SO₄ ²⁻ and organic acid anions in surface soil horizons, with SO₄ ²⁻ and NO₃ ⁻ below the effective rooting zone, and SO₄ ²⁻ and HCO₃ ⁻ in streamflow. Mineral soil horizons could adsorb little additional SO₄ ²⁻ or associated cations at current soil solution SO₄ ²⁻ concentrations. Therefore it is concluded that the soil in situ lacks a strong affinity for SO₄ ²⁻. Current annual inputs to the forest of SO₄ ²⁻ and NO₃ ⁻ in bulk precipitation (26.4 and 18.2 kg ha⁻¹, equivalent to 8.8 kg S and 4.1 kg N ha⁻¹ , respectively) contributed significantly to cation leaching from the soil. In order to maintain exchangeable cations in soil at current levels, a rate of weathering yielding 29.6, 5.0, 4.4 and 2.2 kg ha⁻¹ yr⁻¹ of Ca²⁺, Na⁺, Mg²⁺ and K⁺, respectively, would be required.