The role of channel-floodplain interactions in the fluvial transport and sequestration of sediments in the Amazon basin are still poorly documented mainly because of the lack of regional networks. Floodplains can act as an important sink of sediments and heavy metals associated with fine particles. In this study, we present an estimation of the contribution of an Amazonian floodplain to sediment transport and sequestration. The floodplain studied is the "Lago Grande de Curuai", located on the right bank of the Amazon R., across from the city of Óbidos. This floodplain is a complex system of more than 30 interconnected lakes, with a maximum inundated area of 2,300 km², representing 1% of the total flooded areas of the Central Amazon basin. We determined an average sedimentation rate of 400,000 t y-1 from a network of stations monitored for 4 years, analysis of multi-temporal remote sensing images and a hydrodynamic model. This storage represents approximately 0.5 % of the total annual sediment flux of the Amazon River at Óbidos. The associated specific deposition rate approaches 114 t km-² y-1.
A very high temporal variability of the monitored TSS has been observed for the lakes and channels. High sedimentation rates are expected in inter-connection channels with the Amazon R. but this rate is much lower at the “varzea” scale. Deposition kinetics in lakes can be disrupted by the re-suspension process under wind effect as it is regularly observed in white water lakes during the low water stage. Suspended sediment concentrations are ranging from 4 mg l-1 during the flood peak to extreme values during the dry season, 1600 mg l-1, exceeding by more than 6 fold the maximum TSS concentration measured in the Amazon mainstream during the same period.
Submetido por Laurence Maurice-Bourgoin em 11-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)