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.