Interactions between anthropogenic sulphate and marine salts in the Bs horizons of acidic soils in Scotland

In laboratory adsorption experiments, the comparison of podzol Bs horizons from coastal and inland moderately-impacted catchments with those from a severely-acidified inland region has demonstrated the effect of marine inputs on SO₄ ^2– -retention. Moderate sea-salt inputs and low acid deposition leads to the retention of most of the SO₄ ^2– and the release of soluble Mg²⁺; increasing the marine salt loading causes the development of a selectivity towards retention of acidic SO₄ ^2– and the retention of Mg²⁺. In the highly-impacted soil, the marine input caused a decrease in SO₄ ^2– retention in open moorland soils. The opposite occurred under forest, due to the ion-exchange of marine Mg²⁺ for soil Al³⁺, increasing soil acidity towards the pH₀ (Gillman and Uehara, 1980), which is depressed below that of its moorland equivalent.