The vertical distribution patterns, the source and correlation of heavy metals were characterized in the bulk soil and different soil aggregates of arable red soil profile (0-100 cm) in Hunan province. Their response to organic carbons in proflie was explored as well. Principal component analysis (PCA) suggested that elements could be divided into two principal components, the metals of the first group were Zn,Cu,Pb,As,Cd, and the second group metals were Cr, Ni. Priniciple component elements had similar sources. In 0-30 cm, The first group metals decreased with increasing depth, the second group metals increased with increasing depth. The concentrations of typical heavy metals were in the order of Zn >Cr >Cu >Pb >Ni >As >Cd. Cd in each soil layer was severely polluted, Zn was at level of light pollution, while other metals were at clean levels. In terms of different size of soil aggregate, it was found that colloids played an important role in facilitating transport of heavy metals, such as As, Cu, Zn, Cd, Cr, Ni. While Pb was still mainly enriched in clay component (<53 μm). Infrared spectrum analysis showed that the main functional groups of organic carbon were polysaccharide (22.07%-47.13%), aromatic (13.88%-34.37%) and alcohol (21.04%-59.49%). Correlation analysis showed that stable organic carbon such as polysaccharide and aromatic organic carbon could stablize the metals of first group in profiles, which would delay the migration of heavy metals to deeper soil. However, the active alcohol carbon would enhance the migration.
Keywords: colloids; correlation; heavy metal; organic carbon; profile; soil.