Soluble and colloidal translocation of Al, Fe, Si and Mn in an artificially drained French Retisol

An element budget at the profile level revealed that only Si was lost from the soil profile while the leaching losses of Al, Fe and Mn were overcompensated by deposition from the atmosphere. The constant Fe/Al concentration ratios in piezometers and drain waters as well as the breakthrough curves at the drain outlet for individual rainfall events suggested that Fe and Al were exported together and mainly in colloidal form. While this was also partly true for Si, a longer tailing of the Si than the Fe and Al breakthrough curves indicated that Si was additionally transported in soluble form. Lastly, the temporal variation of the Mn concentrations was unrelated to that of the other elements, pointing to the predominance of translocation in soluble form. All these results demonstrated that: i) particle/colloidal translocation is more important than translocation in soluble form in a drained Retisol; ii) reductive solubilisation of Fe and Mn oxides still occurred, in spite of the artificial drainage; iii) processes such as wet and dry deposition, dissolution of quartz or ferrolysis also contribute to element budgets in Retisols, at least at some microsites and in some years.