Rivers Amazon

Figure 4 Measurements of (A) uranium aetivity ratios, UARs ( U U) and U eoneentrations (B) aeross a salinity gradient off the Amazon River mouth (1996). UARs were determined by thermal ionization mass speetrometry (TIMS) at Calteeh (D. Poreelli) U eoneentrations by ICPMS...

Fig. 9-8 Histogram of dissolved solids of samples from the Orinoco and Amazon River basins and corresponding denudation rates for morpho-tectonic regions in the humid tropics of South America (Stal-lard, 1985). The approximate denudation scale is calculated as the product of dissolved solids concentrations, mean armual runoff (1 m/yr), and a correction factor to account for large ratios of suspended load in rivers that drain mountain belts and for the greater than average annual precipitation in the lowlands close to the equator. The correction factor was treated as a linear function of dissolved solids and ranged from 2 for the most dilute rivers (dissolved solids less than lOmg/L) to 4 for the most concentrated rivers (dissolved solids more than 1000 mg/L). Bedrock density is assumed to be 2.65 g/cm. (Reproduced with permission from R. F. Stallard (1988). Weathering and erosion in the humid tropics. In A. Lerman and M. Meybeck, Physical and Chemical Weathering in Geochemical Cycles," pp. 225-246, Kluwer Academic Publishers, Dordrecht, The Netherlands.)...

Franzinelli, E. and Potter, P. E. (1983). Petrology, chemistry, and texture of modem river sands, Amazon River system. /. Geol. 91, 23-39. 

Gibbs, R. J. (1967). The geochemistry of the Amazon River system Part 1, The factors that control the salinity and composition and concentration of suspended solids. Geol. Soc. Am. Bull. 78,1203-1232. 

Stallard, R. F. (1980). Major element geochemistry of the Amazon River system. Ph.D. Dissertation, Massachusetts Institute of Technology/Woods Hole Oceanographic Institution, Joint Program in Oceanography, Woods Hole Oceanographic Institution Woods Hole, MA WHOI-80-29. 

Moore DG, Edmond (1984) Radium and barium in the Amazon River system. J Geophys Res 89 2061-... 

Several studies have examined the partitioning of U on particles and colloids. Results from detailed sampling and particle separation in the Amazon estuary shows that most of the uranium at the Amazon River mouth is associated with particles (>0.4 im) and that >90% of the uranium in filtered water (<0.4 im) is transported in a colloidal phases (from a nominal molecular weight of 10 000 MW up to 0.4 im) (Swarzenski et al. 1995 Moore et al. 1996). Mixing diagrams for uranium in different size fractions in the Amazon estuary reveal that uranium in all size fractions clearly display both removal and substantial input during mixing. 

In more recent studies, Feng et al. (1999) calculated a Th water column residence time of 2 to 12 days in the Hudson River estuary. McKee et al (1986b) determined that " Th was removed on a time scale of a day or less in the very particle-rich environment of the Yangtze River estuary. In the Amazon River estuary, another particle-rich environment, McKee et al. (1986a) determined that the residence time of dissolved " Th ranged from 2 to 4 days. McKee et al. (1986a) also calculated apparent distribution... 

DeMaster DJ, Kuehl SA, Nittrouer CA (1986) Effects of suspended sediments on geochemical processes near the mouth of the Amazon river - examination of biological silica uptake and the fate of particle-reactive elements. Cont Shelf Res 6 107-125... 

We turn our attention to developing a chemical model of water from the Amazon River, using a chemical analysis reported by Hem (1985, p. 9). The procedure in... 

Table 6.7. Calculated molalities (m), activity coefficients (y), and log activities (a) of the most abundant species in Amazon River water...

The resulting species distribution (Table 6.7), as would be expected, differs sharply from that in seawater (Table 6.4). Species approach millimolal instead of molal concentrations and activity coefficients differ less from unity. In the Amazon River water, the most abundant cation and anion are Ca++ and HCOJ in seawater, in contrast, Na+ and Cl- predominate. Seawater, clearly, is not simply concentrated river water. 

Fig. 6.3. Saturation indices of Amazon River water with respect to various minerals (left) calculated directly from a chemical analysis, and (right) computed assuming that equilibrium with kaolinite and hematite controls the fluid s aluminum and iron content.

To construct an alternative model of Amazon River water, we assume that equilibrium with kaolinite (a clay mineral, Al2Si205 (OH)4) and hematite (ferric oxide, Fe203) controls the aluminum and iron concentrations ... 

The species distribution (Table 6.9) calculated for the brine differs from that of seawater and Amazon River water in the large molalities predicted and the predominance of ion pairs such as NaCl, CaCl+, and MgCl+. The complex species make up a considerable portion of the brine s dissolved load. 

Sayles, F. L., and P. C. Mangelsdorf Jr. (1979), "Cation-Exchange Characteristics of Amazon River Suspended Sediment and its Reaction with Seawater", Geochim. Cosmochim. Acta 43, 767-779. 

Bergquist B, Boyle E (2002) Iron isotopic composition of Amazon River. EOS Trans. Am Geophys Union 83 OS12C-0290... 

As shown in Figure 14.8, kaolinite concentrations are highest in tropical and equatorial latitudes, particiflarly off the western coasts of North Africa and Australia (>40%) and the northeastern coasts of Australia and South America (30%). The first two are the result of aeolian transport by the Trade Winds from the Saharan and Australian deserts, respectively. The other two are the result of river input from the eastern Australian continent and the Amazon River. 

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