Distribution and partition of trace metals in the Amazon basin

The distribution of trace metals (V, Cr, Mn, Co, Cu, Zn, As, Rb, Sr, Mo, Cd, Sb, Cs, Ba, U) was investigated in surface waters and associated particulates in the Amazon mainstream (Solimoes and Amazon rivers). Dissolved V, Cu, As, Sr, Ba, U correlate with major ions and appear to be predominantly derived from soluble rocks occurring in the Amazon upper basin. These elements appear conservative in waters and are progressively diluted by less-concentrated waters coming from the lowland and shield areas. A monthly time series obtained at the Obidos gauging station shows that temporal variability of trace element concentrations reflects the source, remobilization and/or biological processes occurring in the channel or in the surrounding floodplain lakes. The trace element concentrations in the particulate matter show a clear relationship with the location of the samples. V, Co, Cr, Mn, Sr, Cs and Ba concentrations are higher in the Solimoes and the Rio Negro is enriched in Fe, Al and Zn. In the Rio Solimoes, V, Cr, Mn, Co, Ni, Zn, Cs and Pb are almost entirely carried by the river particulate matter; Cu, Rb, Sr, Ba and U are transported mainly by the suspended particles, but a dissolved phase contributes to the transport. In the Rio Negro, the proportion of elements transported by the dissolved phase is higher for the whole set of elements. The implications of these results allow us to compute the fluxes from the Amazon River to the Atlantic Ocean. Copyright (C) 2003 John Wiley Sons, Ltd.