The natural enrichment of ferruginous weathering products and its implication for water quality in the Hunchun Basin, China

In order to evaluate the extent of a natural enrichment of Fe and Mn over t he whole of the Hunchun Basin, the stability of Fe-Mn mineral phases, their status, the weathering rate of source A variety of samples were collected from sediments, soil profiles, and surface soils. In the solutions after a sequentially selective dissolution using sodium pyrophosphate (P), acid oxa late (o), and dithionite-citrate-bicarbonate (d), Si, Al and Fe were domina nt in the d and p fractions, and Mn in the o and p fractions. The results s howed that the existing phases and status of Fe and Mn were distinctly diff erent, and that the abundance of amorphous Mn phases made thermodynamic cal culation difficult. An application of these ferruginous weathering products was therefore made to understand basin development. The first terrace of t ile Hunchun River inferred from it having a higher value in Fe-d/Fe-t. Amor phous Fe phases such as Fe(OH)(3) and Fe-3(OH)(8) were controlling factors of Fe in the thermodynamic calculations. The transformation of the amorphou s Fe phases to more stable phases was hindered by high contents of smectite and gibbsite, amorphous opaline produced from rice roots, and organic phos phate pesticides or fertilizers in soils. Source-rock deduction using water samples suggested granitic weathering. Precipitation around the Hunchun Ba sin is gradually becoming more acidic. Therefore, in the future it is inevi table that ecological and environmental problems related to the Fe phases m entioned above will occur in the drinking water supply for this area, espec ially in that of the first terrace.