Soluble and particulate transfers of Cu, Cd, Al, Fe and some major elements in gravitational waters of a Podzol

Abstract

The particles moving in suspension through the soil can carry heavy metals with them. We have studied over two years the movement of Cu, Cd, Zn, Al, Fe, Ca, K, Mg, Na and Mn in this way with small open tension-free lysimeters installed in a Podzosol (French classification). Soil solutions were filtered through 0.45 μm membranes and analysed for the composition of the soluble fraction. The membranes were digested to obtain the elemental composition of the particulate matter. The particulate matter ( > 0.45 μm) was substantial and accounted for up to 40% of the total elemental mass-balance for Cu, Cd, Zn, Al and Fe, depending on the horizon. Copper occurred in the particulate fraction of all the horizons. Cadmium and Zn showed a pattern of distribution in the particulate fraction similar to those of Al and Fe. They may thus be associated with these elements, and possibly the organic matter also, forming sesquioxide-organic complexes similar to those found in the solid phase of the soil. Potassium, Ca, Mg and Na were not found in the particulate matter. Thus calculations made with the soluble-only fraction underestimated the total fluxes. The largest particulate and soluble fluxes were found under the E and BPh horizons. This suggests that the BPh horizon looses matter (soluble and particulate) which migrates deeper into the soil profile. The smallest particulate and soluble fluxes were always measured under the illuvial (BPs) horizon. Thus most elements tend to be immobilised in this horizon. Variation in the metal concentration of the soluble fraction was found through the time period. This variation was reduced by the addition of the metal concentrations found in the particulate fraction.