The Anavilhanas and Mariuá Archipelagos: Fluvial Wonders from the Negro River, Amazon Basin

Abstract

With a mean annual discharge of ~29,000 m3 s−1, the Negro River ranks as the sixth in the world in terms of water discharge and is the second largest tributary of the Amazon. The Mariua and Anavilhanas are two huge, fascinating archipelagoes of the Negro River that sustain the largest flooded “igapo” forest systems in the world and rich fish diversity. This chapter presents how hydro-geomorphology and changes in environmental conditions controlled the formation and functioning of these two anabranching reaches in the Negro River. The present hydro-sedimentary dynamics is not compatible with the existing morphology, which is product of a Middle-Late Holocene history. The very low amount of suspended sediment transported by the Negro is not sufficient to construct the intricate islands and floodplain. This condition produces a permanent non-equilibrium stage that controls not only river geomorphology but also vegetation distribution. As a product of long history, the Negro River basin with its wonderful pristine fluvial archipelagos and the “igapo” forests faces their most dangerous enemy: The irrecoverable destruction of the Amazon Rivers by the environmentally irresponsible dam construction planned by the Brazilian government.