The biogeochemistry of basic cations in two forest catchments with contrasting lithology in the Czech Republic

The biogeochemistry of Ca, Mg, K, and Na were investigated in two forested catchments in the Czech Republic, one underlain by leucogranite, the other by serpentinite. High weathering rates at the serpentinite site at Pluhuv Bor resulted in Mg²⁺ as the dominant cation on the soil exchange complex and in drainage water. Other basic cations (Ca²⁺. K⁺, Na⁺) showed relatively low concentrations and outflow in streamwater. The catchment exhibited high base saturation in mineral soils (>70%), and near neutral soil and stream pH, despite elevated inputs of acidic deposition. Slow growth of Norway spruce at Pluhuv Bor may be caused by K deficiency, Mg oversupply and/or Ni toxicity. In contrast, the granitic site at Lysina showed low concentrations of basic cations on the soil exchange complex and in streamwater. Soil and drainage water at Lysina were highly impacted by acidic deposition. Soil pH was extremely acidic (<4.5) throughout the soil profile, and the base saturation of the mineral soil was very low (<5%). Supplies of basic cations from atmospheric deposition and soil processes were less than inputs of SO₄/^2- on an equivalence basis, resulting in low pH and high concentrations of total Al in drainage water. Needle yellowing in Norway spruce was possibly the result of Mg deficiency at Lysina. Because of their extremely different lithologies, these catchments serve as valuable end-members of ecosystem sensitivity to elevated levels of acidic deposition.