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Concentration of different iron fractions in a sediment profile of Lake Kasin. White bars, 0.5 M HCl-extractable (bioavailable) iron. Black bars, crystalline iron, extracted during incubation in 6 M HCl at 70°C for 24 h. Iron concentrations in the extracts were determined with the ferrozine assay (82). Error bars represent standard deviations calculated from duplicate samples.
