Chemical distribution of trivalent iron in riverine material from a tropical ecosystem: a quantitative EPR study

Distribution of trivalent iron has been measured in riverine materials from a tropical hydrosystem (Nyong basin, South Cameroon, central Africa). The speciation and the respective amounts of the iron species have been determined using electron paramagnetic resonance spectroscopy on freeze-dried samples separated by ultrafiltration. Trivalent iron occurred mainly in two forms, linked to organic matter (Fe–OM) and as iron oxides. In the Nyong, Fe occurred mainly as oxides (82%), while in the Mengong, a minor river, it was mainly linked to organic matter (64%). This indicates that iron in suspended matter results from mechanical erosion in the main river and from chemical erosion in the minor river. Moreover, the similar size distribution of Fe–OM in both rivers suggests a conservative inheritance of organics-mediated transport of iron in the hydrographical network.