Interaction between interstitial water and sediment in two cores of Lac Léman, Switzerland

Abstract

The pore fluids of the sediments collected at the deepest point of Lac Léman (Switzerland) are supersaturated with respect to vivianite and siderite. In the presence of sulphide, the iron solubility is controlled entirely by the amorphous iron sulphides. As the iron (II) becomes dominant, the formation of siderite occurs and evidence of this, in the solid phase, can be obtained by the use of Mössbauer spectroscopy and some sequential chemical extractions. The amount of ‘siderite iron’ decreases from about 10% near the sediment surface to a few percent in the lower levels of the sediment (<10 cm). Evidence for vivianite formation could not be obtained even in the lower layers, despite the precautions taken to avoid oxidation. Although the trace metal behaviour in the solid phase is well correlated with the iron and manganese, availability in the pore fluid is dependent on the adsorption on, or co-precipitation with, finely dispersed colloids, which pass through a 0.45 μm filter. Trace metal concentrations in pore fluid were not directly related to total elemental concentrations in the solid phase, and did not reflect cumulative trends associated with anthropogenic enrichment.