Heavy metals mobility in experimental disturbed and undisturbed acid soil columns in Spanish Pyrenees
In this study we explore the processes of sorption and mobility in experimental soil columns in order to assess the response of natural soils to a hypothetical increase of pollution. The soils were sampled in a forest catchment situated in the Bertiz Natural Park at the western end of the Pyrenees. 21 columns, reproducing 21 soil profiles, were treated with a solution of heavy metals four times more concentrated than under actual conditions of deposition. An undisturbed soil column was tested simultaneously. The competition between cations and the content of clay and oxi-hydroxide compounds in the soils were the main factors determining the mobility of metals along with the influence of temperature. Calculated distribution coefficients show retention of Cr3+ Cu2+, and As5+, and in a lesser extent of Pb2+ and leaching of Mn2+, Zn2+, Cd2+ and Ni2+. Consequently, Mn2+ and Zn2+ have a greater tendency to contribute to groundwater pollution, whereas Cr3+ and Cu2+ are more likely to remain on soil surface. In undisturbed soil column, Ni2+ and Zn2+ were preferably sorbed onto dissolved organic matter (DOC), and the sorption of Mn2+ Cu2+ and Zn2+ was controlled by the ambient temperature. The simulation shows the presence of weakly sorbed metals and of others clearly desorbed (Ni2+, Cd2+ and Pb2+), which suggests that in the near future they will reach groundwater becoming a risk for its quality and for the biota. This kind of experiments in disturbed soils did not prove to be successful, hence their analysis in undisturbed soils is suggested.