Effects of simulated precipitation acidified with sulphuric and/or nitric acid on the throughfall chemistry of Sitka spruce Picea sitchensis and heather Calluna vulgaris

Simulated acid rain was shown to increase the leaching of cations from Sitka spruce and Calluna. The sum of the cations (Mg²⁺, Ca²⁺, Mn²⁺ K⁺ and Na⁺) was linearly related to the extent of H⁺ uptake (neutralisation) by young Sitka spruce trees. The response of Sitka spruce branches to a progressive decrease in [H⁺] in the simulated rain over 1 h was a rapid decrease in Ca²⁺, Mg²⁺ and K⁺ leaching. For both simulated mist and simulated rain at pH 3·5 cation leaching was greater as a result of acidification with H₂SO₄ rather than HNO₃ or an equinormal mixture of both acids; no significant difference was found between cation leaching when the rain was acidified with HNO₃ or the HNO₃/H₂SO₄ mixture. The leaching of total organic carbon, NO₃⁻, SO₄²⁻ and Cl⁻ was not affected by the acidity of the rain. However, some uptake of NO₃⁻ was observed when Sitka spruce was exposed to simulated rain acidified with HNO₃.