RIO NEGRO, AMAZON: SOME INTERESTING FEATURES

Rio Negro, the "Black River" (translated literally into English) is not exactly "black", but it is similar in colour to "strong tea". It is the largest left tributary of the River Amazon. It is the third largest river in the world in water volume; it is the largest blackwater river in the world, and one of the world's ten largest rivers in average discharge.

Rio Negro (black water) and Rio Solimões (brownish water), after their confluence they form the Rio Amazonas. Manaus is the largest city in the Amazonian region, capital of the state of Amazonas

Manaus, the capital of the state of Amazonas (on top of the photo), is situated on the  left bank of Rio Negro, in the confluence of this river with Rio Solimões.  After their confluence, the river is called  Rio Amazonas

Rio Solimões (brownish water, rich in sediments) in the confluence with  Rio Negro (black colour)

"Encounter of the waters" of rivers Solimões (brownish colour) and Negro (black colour)

Rio Cuieiras, a tributary of Rio Negro

A navigable canal in the Rio Negro

The Rio Negro basin drains an area of 10% of the 7 millions square km of the Amazon basin. The region of Alto Rio Negro (high River Black) has the highest rainfall in the Amazon, reaching more than 3500 mm. Three main types of ecosystems exist in Rio Negro region:  high, wet and dense forest on clayey soils; the Amazonian caatinga ("campinarana", as it is called in Brazil); and periodically flooded forests situated on banks of black water rivers ("igapós"). Dense forests contribute to a high content of organic acids in the water of Rio Negro, which explains partly the dark colour of the water.
But, more recently, it was observed the presence of high contents of a bacterium, Chromobacterium violaceum which is a Gram-negative, facultative anaerobic, non-sporing coccobacillus. It is part of the normal flora of water and soil of tropical and sub-tropical regions of the world. It produces a natural antibiotic called violacein, which may be useful for the treatment of colon and other cancers. This condition may explain, partly, the small number of fishes in the Rio Negro, as compared to richness of ictiofauna in the Rio Solimões. Some authors suggest that violacein would affect negatively, the proliferation of plancton. The basis of the food chain in the Rio Negro waters.

Brazilian scientists have sequenced the genome of this bacterium and made its deposit in the National Institute of Health of the United States.