Sulfate in rivers

Sulfate is principally derived from the weathering of CaS04 minerals (gypsum and anhydrite) in sedimentary rocks. Some sulfate in rivers, however, comes from the weathering of magnesium sulfate salts in sedimentary rocks and from oxidation of sulfides (primarily FeS2. pyrite) in sedimentary and crystalline rocks. The latter process also liberates small amounts of the cations Ca2+, Mg2+, Na+, and K+ by reactions like ... 

In measurements of dissolved sulfate in rivers, the fact that flowing water may not readily mix laterally or vertically has often been ignored. For example, the Mackenzie and Liard rivers of northern Canada were found to require a distance of the order of 400 km below their confluence before lateral mixing was achieved (Krouse and Mackay, 1971). In another study of this same river system, Hitchon and Krouse (1972) used chemical data and factor analyses to relate qualitatively large variations in the sulfur isotope compositions of dissolved sulfate to a number of geological sources, despite the fact that biological activity had probably altered both the concentrations and ratios. 

O. Kondo, H. Miyata, K. Toei, Determination of sulfate in river water by flow injection analysis, Anal. Chim. Acta 134 (1982) 353. 

As a specific example, consider oceanic sulfate as the reservoir. Its main source is river runoff (pre-industrial value 100 Tg S/yr) and the sink is probably incorporation into the lithosphere by hydrogeothermal circulation in mid-ocean ridges (100 Tg S/yr, McDuff and Morel, 1980). This is discussed more fully in Chapter 13. The content of sulfate in the oceans is about 1.3 X lO TgS. If we make the (im-realistic) assumption that the present runoff, which due to man-made activities has increased to 200 Tg S/yr, would continue indefinitely, how fast would the sulfate concentration in the ocean adjust to a new equilibrium value The time scale characterizing the adjustment would be To 1.3 X 10 Tg/(10 Tg/yr) 10 years and the new equilibrium concentration eventually approached would be twice the original value. A more detailed treatment of a similar problem can be found in Southam and Hay (1976). 

The evaporite source is characterized by covariation of sulfate (from gypsum) and chloride (from halite). That elements can be recycled from the ocean to land by movement of saltbearing aerosols (so-called "cyclic salts") has confused the interpretation of river flux data somewhat. While this cycling generally follows the ratio of salts in the sea, the S/Cl ratio is an exception. Taking the S/Cl ratio of the cyclic component to be 2 (based on compositional data for marine rains) and assuming that all chloride in rivers is cyclic, an upper limit for the cyclic influence can be calculated. 

The river Ebro is characterized by high water conductivity mainly because of its geology. The abundance of gypsum is mainly responsible for the salinity increase of the river water mostly due to the inputs of chlorides and sulfates in the Ebro... 

In contrast to the fate of silicates, a catchment exhibiting a small area of so-called Biindner Schiefer, a sandy-marly schist containing soluble anhydrite or gypsum, will produce a remarkably high weathering rate for the entire basin. This effect arises in the alpine catchments of the Ticino, Rhine, and Rhone. The occurrence of Biindner Schiefer also causes sulfate concentrations in the range of 0.5-1 mmol in rivers. Natural and anthropogenic atmospheric sulfur... 

Figure 9. Analysis of anions and cations in river water using tartaric acid/18-crown-6/methanol-water eluent with a carboxylated polyacylate stationary phase in the protonated form. Ions 1) sulfate 2) chloride 3) nitrate 4) eluent dip 5) unknown 6) sodium 7) ammonium 8) potassium 9) magnesium 10) calcium (from ref. 80)...

The average isotope compositions of the sulfate sulfur in the oxic and anoxic zones are + 18.5%o and + 19.5%, respectively. The isotopic composition of sulfate in the Black Sea forms from two distinct sources. The sea receives annually about 2.82 x 106 tons of sulfate with river discharge with the average isotope composition of + 4.6% [71]. The annual input with Mediterranean waters of 540 x 106 tons of sulfates has an isotopic composition of about + 19.8%o [18]. The isotopic composition of dissolved sulfide averaged over all depths is - 39.6 1.3%o and varies between - 42.0%o and - 32.6%o for all stations [65] (Fig. 5). There is no indication that the sulfur isotopic composition of hydrogen sulfide changes spatially and/or seasonally. 

Isobe et al. [20] extended the seope by analysing both estrogens like estradiol, estrone, and estriol, and their sulfate and glucuronide eonjugates in river water, lake water, and STP samples. SPE in eombination with negative-ion LC-ESl-MS-MS in SRM mode was used. Method deteetion limits between 0.1 and 3.1 ng/1 were reported. While the free steroids and some of the sulfates were deteeted in environmental samples, most of the eonjugates were below the deteetion hmit. 

Hence the Archaean sulfur cycle (Fig. 5.5) would comprise inputs into the atmosphere and oceans from volcanic gases and into the oceans from hydrothermal activity but not river-borne sulfate. In addition, in the anoxic oceans, the oxidative alteration of the ocean floor would not take place. Thus the surface sulfur reservoir would have been small and most sulfur recycled back into the mantle as sulfide minerals. The sulfate part of the sulfur cycle is unlikely to have been fully operational until the late Proterozoic (Canfield, 2004). 

As a specific example, consider oceanic sulfate as the reservoir. Its main source is river run-off (preindustrial value 100 Tg S/year) and the sink is probably incorporation into the lithosphere by hydrogeothermal circulation in mid-ocean ridges (100 Tg S/year, McDuff and Morel, 1980 cf. Chapter 13). The content of sulfate in the oceans is about... 

Analyses of trace metal and sulfate in pore water provide evidence of diagenetic change in salt-marsh sediment. Rapidly processed cores from the Indian Neck and Farm River sites showed normalized SO4/CI ratios of greater than 1 at certain depths (Table VI). The cores also contained measurable concentrations of dissolved Mn and, at the Farm River site, Fe. The high Mn concentrations seen in Figs. 9 and 10 coincide with the maximum SO4/CI ratio. Other metals were not detected, with the possible exception of trace amounts of Zn in one Indian Neck core. 

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