The floodplains of the Amazon basin influence the hydrology and fluxes of suspended solids and solutes on multiple scales. Our study focused on the floodplain of Lago Grande de Curuaí (Óbidos, Brazil), a 4000 km 2 segment of floodplain and local upland catchment representative of the lower Amazon. Based on in situ and satellite data acquired from 1997 to 2003, we calculated the exchanges of water between the floodplain and the river and determined the temporal dynamics of flooded area water derived from river flooding, rainfall, runoff, and exchange with groundwater annually for six years. The Amazon River dominated the inputs of water to the flooded area year-round, accounting about 77% of the annual total inputs; rainfall and runoff accounted for about 9% and 10%, respectively, while seepage from the groundwater system accounted for 4%. The hydrologic residence time of the lake was about three months, and the floodplain made a net contribution of water to the river. The exported volume (net balance between water input and 0022-1694/$ -see front matter ª a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l losses) varied between 4.2 and 7.3 km 3 depending on the year and represented about 0.75 times the maximal storage reached each year. ª

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[1] We present a comprehensive dissolved rare earth element (REE) data set for the Amazon River and its main tributaries, Rio Negro, Solimões, and Madeira, as well as the Curuaí floodplain. The two-year time series show that REE vary seasonally with discharge in each of the tributaries, and indicate a hydrologically dominated control. Upper crust normalized REE patterns are relatively constant throughout the year, with Ce/Ce* anomalies being positively related to discharge. We propose revised annual dissolved REE fluxes to the surface Atlantic Ocean based on an integration of the seasonal data. For Nd (<0.22 mm) this results in an average flux of 607 ± 43 T/yr, which is at least 1.6 times larger than the previous estimate of 374 T/yr (<0.45 mm) based on low water stage data. Moreover, during the high water season the maximum Nd flux measures 1277 t.yr À1 , constituting 30% of the required flux to the Atlantic Ocean (Tachikawa et al., 2003). Consequently, a smaller contribution of Nd from atmospheric and river particle desorption is required than was previously suggested. A mass balance of Amazon tributaries and observed fluxes at Ó bidos indicates that dissolved LREE behave quasi-conservatively. Conversely, the HREE mass balance presents a deficit during the high water stages, which could be related to the passage of water through the floodplain system accompanied by solid/dissolved phase transfer.

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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.