A study of iron and manganese transformation in the oxygen /sulphur(-II) transition layer in a eutrophic lake (lake Bret, Switzerland): a multimethod approach

A refined multimethod approach was developed to collect detailed information on iron and manganese species by mineralizing the possible artefacts often produced by separation of preconcentration techniques. Water samples and in situ measurements came from the deepest part of the lake; samples were taken at 0.5 or 1 m intervals. Samples were analysed by differential pulse polarography, colorimetry, atomic absorption and filtration. The relative abundance of particulate, colloidal, and electroactive species of iron and manganese, and the redox potential across the interfacial zone, were determined. Significant differences in the signals of iron(II) and sulphur(-II) were observed. Natural manganese contained both reactive and non-reactive fractions. The oxygen/hydrogen sulphide transition layer was conveniently represented by division into three distinct redox zones. Development of additional techniques with greater physicochemical selectivity was recommended. A bibliography of 47 references is appended.