Chemical and mineralogical characterization of the sediments from the Mira, Ilhavo and Ovar channels of Aveiro Lagoon (Portugal)

The paleoenvironmental reconstruction of Aveiro Lagoon is being carried out based on the sedimentological, paleoecological, geochemical and mineralogical characterization of sediment samples collected systematically in the lagoon. This paper presents results concerning the changes in the chemical and mineralogical composition of the fine fraction (< 63 mu m) and the clay fraction (< 2 mu m) in sediment samples from Aveiro Lagoon, mainly collected from the lower intertidal plain and subtidal deposits located along the Mira, Ilhavo and Ovar channels. A zonograpby of the lagoon was established based on the parameters analyzed. The results show that the surface and near-surface sediments of Aveiro Lagoon trap relatively large quantities of trace metals, such as Cu, Pb, Co, Ni, Cd, Zn, Fe, Mn and Cr, considered to be partially adsorbed, particularly on silty and clayey particles, and co-precipitated on Fe and Mn oxyhydroxide forms precipitated in the topmost layers of sediments. Series of statistically significant relationships were established between trace metal concentrations and clay content and semi-quantitatively determined clay mineral species in the sediments.