INTERELEMENT RELATIONSHIPS IN IRON-MANGANESE CONCRETIONS FROM A CATENARY SEQUENCE OF YELLOW-GREY EARTH SOILS IN LOESS

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Abstract
Fe-Mn concretions and their surrounding soil materials from the AB and B1g horizons of a catenary sequence of yellow-grey earth soils (Aquic Fragiochrepts) in loess were studied. Concretions were abundant in the AB horizon (29% of whole soil) at the lowest site in the sequence, and Mn translocated downslope more readily than Fe. The elements Ti, Co, S, P, Mo, Cu, V and in some cases Ba, Zn and Ni were enriched in the concretions relative to the soil materials which surround them. Linear regression analysis showed significant positive relationships between Fe and Ti, P, Mo,V, S and Cu, and between Mn and Zn, Co, Ni, Ba and P. The Fe-P relationship was more significant statistically than the Mn-P relationship. Fe was not significantly correlated with Mn. These relationships were attributed to the different surface charges of Fe and Mn oxides at the natural pH values of the soils. Iron oxides and oxyhydroxides, being positively charged or near neutral, attracted oxyanions, especially those with strong specific surface interactions; Mn oxides, being negatively charged, attracted cationic species.

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