ORGANIC-ACIDS IN A MODER TYPE HUMUS PROFILE UNDER A MEDITERRANEAN OAKFOREST

The chemistry of the soil solution in an acid mediterranean forest soi l with a moder type humus profile was studied. Aqueous extracts of ect organic horizons were characterized by high contents of basic cations (Ca, Mg, K and Na) and much lower concentrations of inorganic anions. The resultant apparent anion charge deficit could be explained by a su bstantial dissociation of dissolved organic acids, in particular fulvi c acid, into organic anions. Soil solution chemistry of mineral horizo ns sampled with porous cups also showed an apparent ionic charge imbal ance which correlated positively with the concentration of dissolved o rganic carbon (DOC). In the mineral soil both DOC and basic cation con centrations decrease with depth. Aluminium and iron concentrations wer e positively correlated with DOC concentrations, and decreased with de pth. Both correlations indicate that soluble organic acids, which show a similar behaviour to the fulvic acid fractions of the ectorganic la yer, are able to migrate through the soil profile during the wet seaso n.