Solimoes River

Figure 2.5 Rainfall and river variability in Amazonia, (a) Rainfall in the northern Amazonia, (expressed by the NAR index, Marengo [1992]), (b) discharges of the Amazon River at Obidos, (c) Solimoes river at Manacapum, (d) Tapajoz River at Santarem, (e) Tapajos River at Itauituba (Marengo and Hastenrath 1993).

At the confluence of the Japura and Solimoes rivers, two forest sites of Mamiraua are described by Ayres (1993) with respect to the influence of inundation period on species composition. From the western Amazon there are inventories from the Rio Uyacali (Marmillod 1982), Rio Jurua (Campbell et al. 1992) and Rio Napo (Balsev et al. 1987), and in the eastern Amazon there are inventories from the Rio Guama (Pires and Koury 1959) and the Rio Xingu (Campbell et al. 1986). An overview of sample size, number of species and stems of these inventories is given on Table 13.5. 

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... 

Albemaz, A, L. K. M., and J. M. Ayres. 1999. Selective logging along the Middle Solimoes river. In Varzea. Diversity, Development, and Conservation of Amazonia s Whitewater Floodplains, eds. C. Padoch, J. M. Ayres, M, Pinedo-Vasquez, and A. Henderson (The New York Botanical Garden Press, New York), pp. 135-151. 

Klinge, H., J. Adis, and M. Worbes. 1995. The vegetation of a seasonal VSrzea forest in the lower Solimoes river, Brazilian Amazonia. Acta amazonica 25 201-220. 

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. 

Seasonal variation in chemical distributions in the Amazon (Solimoes) River A multiyear time series." Global Biogeochemical Cycles 9 307—328. 

Figure 16.6 Variations of the trace element dissolved concentrations along the Solimoes River and Amazon mainstream (real distances between stations are not respected).

Figure 16.8 Mass proportions of trace element transported as dissolved and particulate forms in the Solimoes River at Manacapuru, in the Negro River at Paricatuba (Manaus), and in the Amazon River at Obidos.

Konhauser, K.O. Fyfe,W.S. Ferris, F.G. Beveridge, T.J. (1993) Metal sorption and mineral precipitation by bacteria in two Amazonian river systems Rio Solimoes and Rio Negro,... 

El Nino) are mutually consistent, while the rest of the years do not show consistency. In fact, the river data show a period of relatively large discharges between 1972 and 1979 at the Solimoes basin, also observed at the Tapajos River and the main Amazon stream. 

In principle, the records at Obidos should reflect the rainfall regimes from the Negro River, together with the Solimoes, Madeira and Pums. Chu (1982) found that two thirds of water level variability of the Amazon River at Manaus can be explained by the volume of... 

Meites, L. A. K., T. Dunne, and L. A. Martinelli. 1996. "Channel-floodplain geomorphology along the Solimoes-Amazon River, Brazil." Geological Society of America Bulletin 108 1-18. 

Meade, R. H., T. Dunne, J. E. Richey, U. dos Santos, and E. Salati. 1985. "Storage and remobilization of sediment in the lower Amazon River of Brazil." Science 228 488-490. Mertes, L. A. K., T. Dunne, and L. A. Martinelli. 1996. "Charmel-floodplain geomorphology of the Solimoes-Amazon River, Brazil." Geological Soc. Amer. Bull. 108 1089-1107. 

DNAEE 1994), and the proportion of water originated from the Solimoes, Negro and Madeira rivers varies with total discharge during the annual cycle (Molinier et al. 1996). 

Following Martinelli et al. (1989), the mineralogical composition of the particulate material in Amazon River is dominated by quartz and plagioclases, with a minor amount of kaolinite and smectites. Sediment transported by the Solimoes tributaries also shows the presence of quartz, gibbsite and kaolinite. Vermiculite is detected in the Rio I a and Rio Madeira, and mica is represented in the Rio Negro. 

In Fig. 16.5, the suspended matter composition of the Amazon major tributaries is compared with mean trace element concentration for the varzea (Konhauser et al. 1994), and with the average composition of the surficial rocks exposed to weathering, computed by Martin and Meybeck (1979). Among the major tributaries of the Amazon River, the Rio Solimoes presents the highest concentrations for all the elements studied, with few exceptions POC, Zn, Fe, and Pb concentrations are more elevated in the Rio Negro, Co and Ni are in the same range in... 

In the Rio Solimoes, V, Cr, Mn, Co, Ni, Zn, Cs, and Pb are almost entirely carried by the river particulate matter Cu, Rb, Sr, Ba, and U are transported mainly by the suspended particles, but dissolved phase contribute to the transport. Only As is transported predominantly in a dissolved form. 

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).

Coari River, Amazon River system Obtained from J. Edmond (MIT). The sample was collected with a dredge from Station 5 (0.4°04.1 S, 63°09.1 W), which is 1 km from Rio Solimoes. 

As a whole, this process has profound implications for metal cycling in rivers which drain highly leached and low relief podsolitic terrains. The interaction between dissolved organics and dissolved solutes may, however, be limited in other Amazonian river systems. In the Rio Negro, where suspended solids are found in extremely low concentrations, the humic substances behave rather conservatively with a HA FA of 0.64. However, in the Amazon mainstream, the hydrophobic humic acids become selectively adsorbed onto fine suspended particles fi-om the Rio Solimoes (6), such that the HA FA drops to only 0.31 (7). Although the fiilvic acids are compositionally hydrophilic, and therefore, are not readily adsorbed onto detrital material, the drastic loss of humic acids could result in a decrease in available reactive sites for organo-metallic interactions. 

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