Dissolved load in rivers

Their contribution to the total dissolved load in rivers can be estimated by considering the mean composition of river water and the relative importance of various rocks to weathering. Estimates (18) indicate that evaporites and carbonates contribute approximately 17% and 38%, respectively, of the total dissolved load in the wodd s rivers. The remaining 45% is the result of the weathering of siUcates, underlining the significant role of these minerals in the overall chemical denudation of the earth s surface. 

The most stable minerals are often physically eroded before they have a chance to chemically decompose. Minerals that decompose contribute to the dissolved load in rivers, and their solid chemical-weathering products contribute to the secondary minerals in the solid load. The secondary minerals and the more stable primary minerals are the most important constituents of clastic sedimentary rocks. Consequently, the secondary minerals of one cycle of erosion are... 

The net increase in dissolved-P release from land due to human activities also includes deforestation (plus concurrent soil loss), sewage, and waste sources (Fig. 4). Deforestation, typically by burning after selective tree harvesting, converts the standing stock of P in plant matter to ash. This P is rapidly leached from the ash and transported as dissolved loads in rivers this transfer can happen on timescales of a year or two (Schlesinger 1997). Furthermore, the lack of rooted stability on the landscape results in... 

There are two principal ways to selectively partition different elements between the dissolved and solid loads in rivers by selective chemical weathering of particular primary... 

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.)...

Meybeck, M. (1983) Atmospheric inputs and river transport of dissolved substances in dissolved loads of rivers and surface water quantity/quality relationships. Inti. Union of Geodesy and Geophysics, Hamburg, Germany. IAHS Publication, pp. 173-192. 

The abundances of trace elements in rivers depends both on their abundances in the continental crust and their mobility during weathering and transport. In order to depict a global solubility trend of trace elements, dissolved concentrations (Cw) are normalized to those of the upper continental crust (Cc) (Figure 2). Data from the continental crust are from Li (2000). In this figure, major elements in river waters are also shown and all normalized concentrations are compared to the value for sodium. It is important to note that the Cw/Cc ratio is a global mobility index rather than a solubility index because, as will be shown below, a number of very different processes contribute to the occurrence of trace elements in river dissolved load. In addition, for a... 

Walling, D.E., Webb, B.W., 1983. The dissolved loads of rivers a global overview. In Dissolved Loads of Rivers and Surface Water Quantity/Quality Relationships. lAHS Publ. no. 141, pp. 3-20. 

Laboratory studies have shown that sediments accumulated (332 ixg kg ) hexachlorobenzene from water (8.3 )ug L ) with a concentration factor of 40 (Laseter et al., 1976). Depuration was relatively long, exceeding that of the biota. Laska etal. (1976) showed that the concentration of hexachlorobenzene in the vicinity of an industrialized zone bordering the Mississippi River between Baton Rouge and New Orleans was 80 times greater in the soil adjacent to the river than in the water. This was due to the suspended and dissolved load in the river water. No specifrc environmental sorption data are available on other monocyclic aromatic compounds. 

The material transported by rivers consists of dissolved ions (dissolved load), sediment suspended in the flow (suspended load), and sediment transported along the bed of the river (bedload). The total load and the proportion of the load represented by these phases varies widely among rivers in different environments. In particular, climate, topography, and erosion influence the amount and composition of riverine sediment loads. 

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