This study focuses on the confluence of two major rivers of the world, the Solimões River (white waters) and Negro River (black waters). Surface suspended sediment samples (SSC) and spectroradiometer taken along transverse profiles at 500 m intervals over a distance of 10 km, as well as satellite images (MODIS) during the hydrological year, were used to follow suspended sediment variability. In January and February, the confluence is dominated by white waters from the Solimões River in the two banks, and in June and July in the right bank by black waters from the Negro River and in the left bank by clear waters from the Solimões River. We found that indirect tools, such as reflectance obtained by spectrometer or MODIS images, can be used to determine surface suspended sediments in a contrasting zone.

Previos estudios describen de manera general la variabilidad anual de los caudales en el curso principal del Amazonas en Brasil, el cual sólo representa el estado general del sistema hidrológico de la cuenca. Por ello, este estudio utiliza una nueva serie de datos que incluye la descarga diaria de 18 subcuencas, con la finalidad de analizar la variabilidad de los extremos regionales en la cuenca del Amazonas. Luego de describir la diversidad de los ciclos hidrológicos anuales, diferentes pruebas estadísticas son aplicadas para detectar tendencias y rupturas de las series temporales. Este estudio muestra que durante el período 1974-2004, la estabilidad de caudales del río principal en Óbidos, se explica por cambios regionales opuestos que involucran principalmente a ríos Andinos: una disminución de la escorrentía en el periodo de estiage, particularmente importante en las region...

Large hydrological systems aggregate compositionally different waters derived from a variety of pathways. In the case of continental‐scale rivers, such aggregation occurs noticeably at confluences between tributaries. Here we explore how such aggregation can affect solute concentration‐discharge (C‐Q) relationships and thus obscure the message carried by these relationships in terms of weathering properties of the Critical Zone. We build up a simple model for tributary mixing to predict the behavior of C‐Q relationships during aggregation. We test a set of predictions made in the context of the largest world's river, the Amazon. In particular, we predict that the C‐Q relationships of the rivers draining heterogeneous catchments should be the most “dilutional” and should display the widest hysteresis loops. To check these predictions, we compute 10 day‐periodicity time ser...

En « Amazonie des rivières », la période de basses eaux permet la mise en culture de vastes zones exondées et fertiles sur les berges des rivières et dans les plaines d'inondation. La variabilité des extrêmes hydrologiques et celle de la structure du cycle de décrue, facteurs réputés importants pour la qualité des récoltes sont explorés à la station fluviométrique de Tamshiyacu sur le fleuve Amazonas. Le riz, culture rentable dans cette région, est notre référence. Les résultats ne présentent pas les liens supposés entre résultats agricoles et durée de la saison de basses eaux ou vitesse de remontée des eaux. Néanmoins, ils montrent la baisse des étiages, l'allongement de la durée de décrue en relation avec un retard de la montée des eaux et une accélération de la remontée des faux pendant la période 1985-2015.

Fluvial sediment dynamics plays a key role in the Amazonian environment, with most of the sediments originating in the Andes. The Madeira River, the second largest tributary of the Amazon River, contributes up to 50% of its sediment discharge to the Atlantic Ocean, most of it provided by the Andean part of the Madeira basin, in particular the Beni River. In this study, we assessed the rainfall (R)-surface suspended sediment concentration (SSSC) and discharge (Q)-SSSC relationship at the Rurrenabaque station (200 m a.s.l.) in the Beni Andean piedmont (Bolivia). We started by showing how the R and Q relationship varies throughout the hydrological year (September to August), describing a counter-clockwise hysteresis, and went on to evaluate the R–SSSC and Q–SSSC relationships. Although no marked hysteresis is observed in the first case, a clockwise hysteresis is described in the second....

The Madeira River is the second largest Amazon tributary, contributing up to 50% of the Amazon River’s sediment load. The Madeira has significant hydropower potential, which has started to be used by the Madeira Hydroelectric Complex (MHC), with two large dams along the middle stretch of the river. In this study, fine suspended sediment concentration (FSC) data were assessed downstream of the MHC at the Porto Velho gauging station and at the outlet of each tributary (Beni and Mamoré Rivers, upstream from the MHC), from 2003 to 2017. When comparing the pre-MHC (2003–2008) and post-MHC (2015–2017) periods, a 36% decrease in FSC was observed in the Beni River during the peak months of sediment load (December–March). At Porto Velho, a reduction of 30% was found, which responds to the Upper Madeira Basin and hydroelectric regulation. Concerning water discharge, no significant change ...

La vida en la región amazónica está principalmente relacionada con la estacionalidad del régimen hidrológico fluvial. La riqueza de la biodiversidad y productividad de la llanura de inundación depende de los nutrientes y la materia orgánica que son transportados por los ríos en los sedimentos en suspensión, desde los Andes hacia el océano Atlántico. Sin embargo, poco se conoce sobre la influencia de la variabilidad hidrológica y pluvial en los flujos sedimentarios. Para abordar esta brecha, analizamos 3069 muestras superficiales de agua y sedimentos recolectadas en el centro del río, cada 10 días durante el período 1995-2014, en 6 estaciones ubicadas en el río Amazonas y sus tributarios. Este análisis se ha realizado haciendo una distinción del tamaño de las partículas, sedimentos finos (arcilla y limo) y sedimentos gruesos (arena). Considerando esta distinción, se e...