In the last decades a wide body of theoretical, experimental, and field research have emerged on the fluvial dynamics of river confluences. To date most experimental studies have focused either on laboratory confluences or on small natural confluences, whereas an extremely limited number of investigations have been conducted on large river confluences. Presently, little is understood about how differences in tributary water physico-chemistry (e.g. temperature, pH, conductivity) are related to local hydrodynamic and mixing processes about confluences, especially large confluences and further how these differences could influence fish biogeography about such confluences.

As part of the Clim-Amazon Project, a field sampling campaign was conducted about the confluence of the Negro and Solimões Rivers in order to better understand the fluid dynamics, sediment transport and mixing within the confluence zone.  A detailed series of ADCP and water quality measurements were collected about the confluence zone, particularly in the mixing zone of black and white waters of these rivers, each with distinct water characteristics. Presented here key findings from this field sampling campaign as well as a conceptual model that helps to explain how tributary water characteristic differences influence local confluence hydrodynamic and mixing processes.  These findings also contribute to the understanding how hydrodynamic and mixing processes about a large confluence with distinct tributary water characteristics may impact fish biogeography and ecology within and downstream the confluence zone. To accomplish this, the findings of this study are compared with those from previous studies on fish biogeography within the Amazon Basin.