Chemistry and speciation of soil water from serpentinitic soils: importance of colloids in the transport of Cr, Fe, Mg, and Ni

This study focused on the chemistry of soil water samples (SWS) obtained by tension-free lysimetry from serpentinitic, i.e., Cr- and Ni-rich, Dystric Eutrochrepts. Soil water samples from undisturbed soil profiles had total elemental concentrations ( mu mol/L) of 0.1-3.2 Cr, 0.2-3.1 Ni, 3-154 Fe, and 55-401 Mg; however, dialysis revealed that on average, only 72% of total Mg, 39% Ni, 28% Cr and 15% Fe were present in dissolved form. Thus, in serpentinitic soils, colloids can be an important means of element translocation. Among metallic cations, Mg contributed generally more than 50% to the positive charge of SWS; also, there was a high linear correlation between dissolved (dialyzable) Mg and electrical conductivity.