Black Amazon river

Phenolics are responsible for the coloration of black-water rivers, particularly in the tropics. An example is the Rio Negro, which remains distinct in its black color for many miles as it flows into the milky brown Amazon. In and near such black rivers, fauna and flora are considered impoverished (Swain, 1979). 

Hedges, J. I, E. Mayorga, E. Tsamakis, M. E. McClain, A. Aufdenkampe, P. Quay, J. Richey, R. Benner, S. Opsahl, B. Black, T. Pimental, J. Quintanilla, and L. Maurice. 2000. Organic matter in Bolivian tributaries of the Amazon River A comparison to the lower mainstream. Limnology and Oceanography 45 1449—1466. 

Most limnological studies have been completed near the confluence of the Solimoes and Negro rivers, which combine at Manaus to form the Amazon River. These rivers are biogeochemically distinct systems. The Solimoes River, called a whitewater river, is rich in dissolved nutrients and suspended sediments and has extensive, fertile flood-plains. The Negro River is nutrient poor and contains high concentrations of dissolved organic carbon, hence it is called a black-water river. 

Hedges J. I., Mayorga E., Tsamakis E., McClain M. E., Aufdenkampe A., Quay P., Richey J. E., Benner R., Opsahl S., Black B., Pimentel T., Quintanilla J., and Maurice L. (2000) Organic matter in Bolivian tributaries of the Amazon River a comparison to the lower mainstream. Limnol. Oceanogr. 45, 1449—1466. 

The endangered black-bearded, or red-backed, bearded saki (Chiropotes satanas) lives between the Orinoco and Amazon rivers and has bare red skin patches on its face. The white-nosed bearded saki (C. albina-sus) lives primarily south of the Amazon. 

Fig. 6-9 Ternary diagram showing proportions of dissolved Si(OH)4, carbonate alkalinity (HCOj + CO3"), and (Q + S04 ) in the Orinoco River and Amazon River basins. Charged species are in equivalents Si(OH)4 is in mole units. The curves in the larger figure are numbered in total cation concentration (mEq/L). Unlike previous figures, symbols represent the total cation concentration interval that includes the sample s concentration. The predominant symbol within each interval corresponds to samples whose concentrations plot within that interval. In the smaller figure, the patterned areas correspond to the predominant source of samples whose concentrations plot within the areas (A) streams that drain cratonic areas (B) streams that originate in mountain belts, but that drain large areas of cratons (C) streams that drain mountain belts with extensive black shales (D) streams that drain mountain belts with extensive carbonate rocks and evaporite deposits. Adapted from Stallard (1988) with the permission of Kluwer Academic Publishers.

On nonflooded sites in Amazonia, species richness increases from east to west, from 87 species ha i near Belem (Black et al. 1950) to over 179 species ha near Manaus (Prance et al. 1976) and more than 200 species in Ecuador (Balslev et al. 1987). Gentry (1982, 1990) explained species richness generally increases as annual precipitation increases. However in the same direction diversity increases in the floodplain forests from 53 species per ha in Para (Pires and Koury 1959) to over 135 species in Mamiraua (Ayres 1993) to 149 species at the Rio Napo (Balslev et al. 1987). The human influence on species composition in floodplain forests is a poorly investigated factor however, forests of the eastern Amazon have been exposed to deforestation and severe exploitation for longer times than western forests. In the varzea of the Solimoes river, selective logging nearly caused the extinction of... 

The behavior of uranium varies considerably across samples studied. Palmer and Edmond (1993) have reported increasing trends of uranium concentration with river alkahnity in the Orinoco, Amazon and Ganga river basins, showing the importance of limestone and black shale dissolution for the control of uranium concentrations in river waters. The association of uranium and major soluble elements is also reported by Elbaz-Poulichet et al. (1999) for the upper Amazonian basins of Bohvia. However, under the organic-rich conditions of Scandinavian rivers (Porcelli et al., 1997) or African rivers (Viers et al., 1997), uranium concentrations can be decoupled from those of major elements, due to the existence of a colloidal fraction of uranium. 

Figure 6 Proportion of elements transported in dissolved (<0.2 pirn) and particulate forms by contrasted rivers of the Amazon Basin the Solimoes (a turbid river, mostly influenced by the Andes) and the Rio Negro (a t)fpical lowland, black river with very low suspended sediments yields).

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