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 SO42--retention. Moderate sea-salt inputs and low acid deposition leads to the retention of most of the SO42- and the release of soluble Mg2+; increasing the marine salt loading causes the development of a selectivity towards retention of ''acidic'' SO42- and the retention of Mg2+. In the highly-impacted soil the marine input caused a decrease in SO42- 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 pH(0) (Gillman and Uehara. 1980), which is depressed below that of its moorland equivalent.