Waters, continental

Fll Burial of sulfur in sediments from continental water bodies — — — — — — 35... 

Cyclodextrin solution for extraction studies was prepared at a concentration of 1.00 x 10" iif by dissolving solid y-CDx in deionized water (Continental Water Systems, Atlanta, Georgia). Fresh solution was prepared daily to prevent bacterial growth and CDx decomposition from interfering with complexation and extraction. Cyclodextrin was purchased from Advanced Separation Technologies, Inc. (Whippany, New Jersey) and was used as received. Solid CDx from one lot number was used for all extractions. 

As discussed elsewhere in this volume, another field where the use of U-series disequilibria has proven to be very useful is the study of chemical transport in waters, either marine (see Cochran and Masque 2003 Henderson and Anderson 2003), estuarine (Swarzenski et al. 2003) or continental waters. In the continental domain, in addition to characterization of transfer processes related to groundwater flows (Porcelli and Swarzenski 2003), radioactive disequilibria have also helped in constraining chemical exchanges between particulate, dissolved and colloidal loads of waters, as well as the origin of chemical fluxes carried by waters. 

Armentano TV, Verhoeven JTA. 1990. Biogeochemical cycles global. In Patten BC, et al., eds. Wetlands and Shallow Continental Water Bodies. Vol. 1. Human and Natural Relationships. The Hague SPB Academic Publishers, 281-311. 

Deionised water from a Modulab system (Continental Water Systems, San Antonio, TX, USA) was used for all solutions. The S-captopril solutions were prepared from standard S-captopril solution (1(V2 mol/L) prepared in citrate buffer, pH 4.00, respectively, by serial dilutions. 

Begemann, F. Libby, W.F. (1957) Continental water balance, ground water inventory and storage times, surface ocean mixing rates and worldwide water circulation patterns from cosmic ray and bomb tritium. Geochemica Cosmochemica Acta, 12, 277-96. 

Koster R. D., De Valpine P., and Jouzel J. (1993) Continental water recycling and stable water isotope concentration. Geophys. Res. Lett. 20, 2215-2218. 

It is now well known that trace-element concentrations in continental waters depend on the size of the pore filters used to separate the particulate from the dissolved fraction. This is apparent in Table 1, where results from the Amazon and Orinoco are reported using two filtration sizes the conventional 0.2 p,m filtration and filtration with membranes of smaller cutoff size (ultrafiltration). These results suggest the presence in solution of very small (submicro-metric) particles that pass through filters during filtration. The view that trace elements can be separated into particulate and dissolved fractions can thus no longer be held this has led authors to operationally define a colloidal fraction (0.20 p.m or 0.45 p.m to 1 nm) and a truly dissolved fraction (<1 nm) (e.g., Buffle and Van Leeuwen, 1992 Stumm, 1993). The existence of a colloidal phase has a major influence on the speciation calculation schemes presented above (based only on aqueous complexation), as the apparent solubihty of trace elements will be enhanced by the presence of colloids. The dynamics of colloids also completely change... 

Geochemical constituents are transported by the circulation of the Earth s three major near-surface dynamic systems the oceans, the atmosphere, and continental water. This chapter deals with the third of these, specihcally with subsurface water. Surface water is an important medium for transporting geochemical constituents on a global scale, and is relatively easily accessed and quantihed. In contrast, subsurface water is not easy to access, and... 

The concentrations of trace metals in continental waters are controlled by atmospheric precipitation and the weathering processes on soils and bedrocks. Because these pathways and processes have been altered significantly by humankind, the flux and distribution of trace metals in a large fraction of all freshwater resources have increased. 

The presence of terrestrial evaporites in the older part of the geological record, for example in the Palaeozoic and beyond, has been taken to indicate the former presence of negative water-balance conditions, and commonly interpreted as palaeo-aridity. Of more interest, in the present context, is the detailed information that is now available on Quaternary continental water-balances from terrestrial sequences containing evaporites. 

Continental water contains dissolved species that render it acidic. The acidity comes from a variety of sources from the dissociation of atmospheric C02 in rainwater—and particularly from dissociation of soil-zone C02 (Section 4.4.2)— to form H2C(and natural and anthropogenic sulphur dioxide (S02) to form H2S03 and H2S04 (see Boxes 3.7 3.8). Reaction between a mineral and acidic weathering agents is usually called acid hydrolysis. The weathering of CaCO, demonstrates the chemical principle involved ... 

In continental waters, bicarbonate (I ICO ) and carbonate (CO2-) ions are the most important components of alkalinity, although in seawater other ions also contribute to alkalinity. The relative importance of HCOf and CO2- depends on the pH of the solution and can be calculated from the known dissociation constants (see Box 4.5) of these ions and the solution pH. 

It is simple to demonstrate that the alkalinity in most continental waters is dominated by HCOf by rearranging the above equations at a typical pH value for these waters. For example, many mature rivers have pH values around 8. Rearranging equation 5.9 to solve for aHCO gives,... 

This shows that at typical pH values for continental waters the HCOf anion is 200 times more abundant than the CO( anion. Repeating this exercise for a range of pH values results in the graphical relationship shown in Fig. 5.5. Note that when pH falls below 5 on Fig. 5.5, almost all of the weak acid anions (HCO, and C03 ) have disappeared and at pH of 4 only undissociated acid (H2C03) remains. This relationship is used as the basis for measuring alkalinity (Box 5.2). 

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