Factors Influencing the Elemental Distribution in Iron-Manganese Cutans of Three Subtropical Soils

Contents and properties of heavy elements in iron-manganese cutans and the corresponding matrix soils of three subtropical Chinese soils (Fragiudalf, Ferrudalf, and Hapludult) were investigated to discern the effect of soil-forming factors on the enrichment of heavy elements in the iron-manganese cutans with respect to the matrices. Results showed that the contents of clay, organic matter (OM), bases, and heavy metal elements were higher in the cutans than in the matrices. Cutans in the Fragiudalf had a neutral pH and higher content of OM and bases than those in the other soils. The cutans in the Ferrudalf were acidic, with increased contents of Fe and Mn oxides. The cutans in the Hapludult were more acidic and clayey than the cutans in the Fragiudalf and the Ferrudalf. Moreover, the contents of free Fe oxides and ratios of extractable noncrystalline Fe oxide/free Fe oxide (Feo/Fed) in the cutans of the Hapludult were higher than those in the other cutans. Compared with the corresponding matrices, the contents of heavy-metal elements in cutans of Hapludult increased more than those in other iron-manganese cutans. The varimax orthogonal factor rotation of factor analysis was chosen to make the statistical test a good fit to show the elemental distribution between the cutans and their corresponding matrices. The results revealed that Mn oxides played a leading role in the enrichment of most heavy metals for the cutans in the Fragiudalf. In the Ferrudalf, Fe oxides strengthen the migration process of the metals to the cutans. For the cutans in the Hapludult, the influence of Mn oxides on the enrichment of heavy metals decreased, and the impact of clay and Fe oxides increased with respect to the cutans in other soils. The factors that affected the heavy metals were the least for the cutans of the Ferrudalf compared with those in the cutans of the Fragiudalf and the Hapludult. The transport of heavy metals from the matrix soils to iron-manganese cutans in the three soils was mainly influenced by the different soil-forming environments and soil compositions. Statistical analysis indicated that the soil-forming factors that affected the enrichment of heavy metals in the cutans were more prominent in the Ferrudalf than in the Fragiudalf and the Hapludult.