No abstract

The trace metal (V, Cr, Mn, Co, ell, Zn, As, Rb, Sr, Mo, Cd, Sb, Cs, Ba, U) concentrations and temporal variabilities of the Amazon river and its main tributaries are studied on time series basis in the major tributaries of Amazon river (Negro, Madeira and Solimbes Rivers) and at Obidos station on the Amazon mainsteem which represents 90% of the total discharge of Amazon river to the Ocean. Variations of river chemistry may reflectvariations of the sources. The "Shield" rivers(as the Rio Negro) have typically depleted concentrations in As, Sr, Ba, Cu, and V as compared with Andean rivers. Elements such Mn and As are mainly transported by the flood flows. These elements are known to be concentrated in lateric (ferricrete) soils which represent 80% in the Amazon basin, suggesting that these elements are washed away in solution during the high discharge. Moreover, these elements can be stored in the surrounding floodplain areas (varzea) where deposition/resuspension cycles as well as the exchange rate between floodplain and mainstream channel may control at least partially the temporal variation of redox element concentrations such Mn and As. Implication on these results on the trace element flux from Amazon River to the Atlantic Ocean is discussed.

Multi-element analysis of plant tissue samples increased thjs last 20 years, in relation to chen1ical weathering processes. However, if plants play a key role in terms of storage and transfer of elements (n1ajor and trace) in natural ecosysterns, our knowledge of transfer processes and fluxes are still poor. In the present study, we measured the concentrations of major and trace elements in the leaves of four different species (annual and perennial) of an amazonian floodplain during one hydrological period. The studied site is the "Ilha de Marchantaria"(3°15'S; 60°00'W) located on the SolimOes River (Upper Aniazon), near the city ofManaus. The results reveal high concentrations (fron1 10 to 1000 ppm fOr Al, Mn and Fe ; from 10 to lOO ppm for Rb, Sr and Ba) in leaves and an annual variation wich is reverse of the river discharge (High concentrations for low water level and low concentrations for high water level). According \Vith datas of net primary production (100 1.ha-1 .y-1) and of total floodplain area (200000 kn1 2 }, we estimate the an1ount o.f trace clcn1ents stored or recycled in the vegetation of the amazon floodplains. We also observed that the amount of trace n1etals exported by the amazon [9] is one hundred tin1e less than the an1ount of trace metals stored or recycled by the vegetation.