Speciation of dissolved and particulate manganese in the Seine river estuary

During four surveys covering various hydrodynamic conditions samples were collected in the Seine river estuary for the study of dissolved and particulate manganese. A new analytical method for direct determination of dissolved manganese was used in this study (atomic absorption spectrometry with Zeeman non-specific absorption correction). Generally, dissolved manganese versus salinity curves exhibits a peak concentration in the low salinity zone. Speciation studies of dissolved and particulate manganese have been performed in order to establish a model for manganese behaviour in the Seine estuary. Taking into consideration the solution composition as well as the values of stability constants of the complexes, dissolved manganese speciation has been calculated using an equilibrium Speciation program. Sequential extraction procedures (Tessierʹs scheme) have been applied to assess the manganese distribution in solid samples (sediment, suspended matter). Operational nature of empiricism inherent to these procedures has been partly eliminated by determining physicochemical form of Mn by electron spin resonance owing to the paramagnetic properties of manganese. This study has allowed us to show that manganese behaviour in the Seine estuary is strongly influenced, (i) in solid samples, by the presence of calcium carbonate which stabilise the Mn(II) form; (ii) in solution, by the increase of salinity, calcium, magnesium and suspended matter concentrations, by complexes formation and by diffusion from sediments to water.