Element fluxes and buffer reactions in acidified soils from a humid-temperate region of southern europe

The present study aimed to assess the buffering reactions and identify the sources of ion replenishment by carrying out a laboratory leaching experime nt using some soils from a humid, temperate region of Northern Spain. The e xperiment consisted of the addition of a solution of H2SO4 to five soils de veloped on various types of parent materials (granulite, serpentinite, schi st, granite and sandy sediments) and differing markedly in their mineralogy and chemical properties. Although the treatment considerably intensified t he leaching of base cations, the exchangeable fraction increased or was not affected, which indicated significant mobilization of these elements from non exchangeable fractions. The soils differed markedly in the amounts of S O42- retained, however only a small part of the amount retained in the uppe r horizons was adsorbed. Acid load was mainly produced by free deposited H and nitrification of internal organic N. Sulphate retention was the domina nt buffering mechanism in the soils developed on serpentinite and schist. P roton consumption linked to Al mobilization occurred in the surface horizon s of all soils, but especially in the most acidic soils, those on granite a nd schist. In the soil on sandy sediments, the dissolution of CaCO3 constit uted the only buffering mechanism.