Аннотация:The present study focuses on the lateral distribution of relatively mobile forms of metals bonded to specific soil particle-size fractions. The study object is a monolithic (loamy) dry U-shaped valley (“balka” in Russian), located in the mixed forest zone of European Russia. In total 50 bulk samples of surface soil horizons were taken along the balka’s three cross-sections and in longitudinal direction. Eleven samples were selected for physical separation into certain particle-size groups: 0.25-0.05mm (fine sand), 0.05-0.01mm (coarse silt), 0.01-0.001mm (medium and fine silt),and <0.001mm (clay). The separated solid phases were analyzed for total concentrations of Fe, Mn, Cu, Ni, Co,Cr, Zn, Pb and their mobile forms extracted by 1N HNO3.
Across the studied particle-size fractions the clay showed the highest average concentrations of the metals’ mobile forms, while the fine sand fraction on average was the most depleted in Cu, Zn, Pb, Co, Ni, and the coarse silt fraction in mobile Cr, Mn, Fe.
The metal mobility (estimated as the ratio between the extracted metal concentration and its total content) tends to increase from the coarser to finer fractions. The clay fraction demonstrated the highest proportions of mobile Mn (126%), Pb (63%), Co (19%), Ni (14%), Cr (10%), however the mobility of Cu and Fe was at its highest in the medium and fine silt fraction (62% and 25%, respectively), while Zn mobility was at its maximum (36%) in the coarse silt fraction.