BEHAVIOR AND SPECIATION OF METALLIC SPECIES CU, CD, MN AND FE DURING ESTUARINE MIXING

This paper, based on laboratory experiments, deals with the behaviour of metallic species Cu, Cd, Fe, Zn and Mn during the mixing of river a nd seawaters. The present study focused on the variations of metals sp eciation in both the dissolved phase and the suspended particulate mat ter. For the dissolved metals, a protocol using chelating resins permi tted to perform trace metals speciation, i.e. fractionation into 'orga nic-metal' and 'inorganic-metal', and to preconcentrate them. The spec iation of suspended particulate matter (SPM) was performed according t o the sequential extraction procedure of Tessier et al., 1979, to part ition particulate metals into five different fractions. All total meta ls had a conservative behaviour. However, there were great differences from one metal to another in the partitioning into dissolved and part iculate phase. For iron, the metal was partly removed from the dissolv ed phase during the mixing, probably because of organic matter floccul ation. Particulate iron was conservative because 90% of it remained in the 'residual' fraction of SPM. Copper had a conservative behaviour i n both the dissolved and the particulate phases. The affinity for orga nic matter was well established for dissolved copper as well as for pa rticulate copper, i.e. respectively 40% in 'organic' form and more tha n 60% in the 'organic' fraction. Manganese and cadmium were non-conser vative: a clear enrichment of the dissolved phase was observed at low salinities (<7.5). These metals were desorbed in inorganic form from t he particulate phase and for a large part from the 'carbonates' fracti on of the SPM. (C) 1998 Elsevier Science Ltd. All rights reserved.