River water composition

Several water compositions are plotted on the stability diagrams in Figure 8.2. It can be seen that at shallow Earth surface pressures and temperatures, seawater plots in the stability field of dolomite whereas solutions of average river water composition and most shallow groundwaters plot in the field of calcite. With burial of carbonate sediments and elevated P and T, the dolomite field shrinks, but subsurface fluid compositions evolve toward a composition in equilibrium with dolomite. This conclusion is probably one of the most important arguments for the formation of dolomite during deep burial diagenesis (see also Hardie, 1987). Thermodynamic considerations favor this reaction path, as well as the fact that... 

Figure 8.2. Phase relations in the system Ca0-Mg0-HCl-H20-(CC>2). At A. 25°C, 0.001 kb B. 150°C, 1 kb C. 300°C, 3 kb. Mag, magnesite Dol = dolomite Calc = calcite Hydro-Mag = hydromagnesite. Saturation lines for brucite (a) and lime (b) are also shown. Average seawater composition, river water composition, A some subsurface water compositions. (After Bowers et al 1984.)...

The magnitudes of chemical kinetic and macroscopic transport processes, evaluated as their linear rates [linear rate=(mass flux)/(concentration or density) = F/p], indicate that great differences exist between the mineral dissolution rates, as reported from laboratory measurements, and the rates derived from river-water composition and volume flow. These differences point to an important role of the physical structure of the weathering zone and water residence time within it that control mineral dissolution fluxes and transport of the reaction products. An additional factor responsible for the faster rates of chemical weathering could be bacterial, activity which may be expected to vary from lower levels in the cold regions to the higher levels in the tropics, in parallel with the rates of net primary productivity. 

Average world river water composition plots close to the cross point of calcite saturation line for Pco2 = 10 atm and electroneutrality line which is approximated as mncos = 2mca2+- This shows that river water with small runoff is in equilibrium with calcite. Therefore, it is inferred that chemical composition of river... 

Fig. 8. Shale-normalized lanthanide compositions of 0.22 (tm filtrates of the Amazon, Fly (Papua New Guinea) and Mississippi River waters. Amazon and Mississippi data from Sholkovitz (1993, 1995) Fly River data from unpublished work of Sholkovitz. G/J Avg. refers to the averaged river water composition of Goldstein and Jacobsen (1988a).

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. 

Table 17-1 Composition and average concentrations of chemicals in seawater and Rhine River water (Duisburg)...

Whitfield, M. and Turner, D. R. (1979). Water-rock partition coefficients and the composition of seawater and river water. Nature 278,132-137. 

Evaporitic sulfur has a range of sulfur isotopic composition from +10%o to +30%o, while sedimentary sulfur is depleted in the heavy isotope and has a range of isotopic composition of about —40%o to +10%o. Most of this variation reflects systematic changes with geological age. The source fractions of a river water can be estimated from an isotopic mass balance ... 

Palmer MR, Edmond M (1992) Controls over the strontium isotope composition of river water. Geochim Cosmochim Acta 56 2099-2111... 

Rona E, Urry WD (1952) Radium and uraninm content of ocean and river waters. Am J Sci 250 241-262 Rosholt J, Doe B, Tatsnmoto M (1966) Evolntion of the isotopic composition of nraninm and thorinm in soil profiles. Geol Soc Am Bull 77 987-1004... 

River inputs. The riverine endmember is most often highly variable. Fluctuations of the chemical signature of river water discharging into an estuary are clearly critical to determine the effects of estuarine mixing. The characteristics of U- and Th-series nuclides in rivers are reviewed most recently by Chabaux et al. (2003). Important factors include the major element composition, the characteristics and concentrations of particular constituents that can complex or adsorb U- and Th-series nuclides, such as organic ligands, particles or colloids. River flow rates clearly will also have an effect on the rates and patterns of mixing in the estuary (Ponter et al. 1990 Shiller and Boyle 1991). 

Table 5. Alteration of chemical composition of the Syr—Daria river water used for drinking by aborigines.

The ion proportions in most river water is significantly different from that in seawater. As a result, river runoff can have a local impact on the ion ratios of coastal waters. This effect is most pronounced in marginal seas and estuaries where mixing with the open ocean is restricted and river input is relatively large. The variable composition of river water and its impact on the chemical composition of seawater are discussed further in Chapter 21. 

Trace elements are discharged into the ocean in particulate and dissolved form as a component of river runoff and groundwater seeps. They are introduced into these waters during the chemical and mechanical weathering of crustal rocks. Thus, the chemical composition of river water is dependent on the composition of the rocks in the... 

Table 21.2 Average Composition of River Water for the Different Continents. ... 

Although the chemical removals of the major ions are slow, they collectively exert an important control on the salt composition of seawater. This is illustrated by comparing the major ion composition of seawater to that of river water as shown in Table 21.8. Although river water is the largest single source of the major ions to seawater, its ion... 

Riparian wetlands are those lands that are periodically inundated with water from adjacent rivers, streams, lakes or other freshwater bodies, and by runoff from upland areas. Large fluxes of energy and nutrients pass through riparian wetlands and they are important sinks and transformers of nutrients. In watersheds with extensive riparian wetlands, the composition of the river water may... 

The water composition of alpine rivers is strongly influenced by natural diffuse inputs originating from rock weathering. Weathering processes are defined as the alteration of rocks in the top crust of the earth it is mainly an interaction of water with rocks [9, 10]. Water can act through physical and chemical processes. 

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