Sulfate Flux

ASoil depth with linear gradient in sulfate concentration = x x = (dx) = 10 cm 

Sulfate concentration C = 30 pg cm Cp = 0 pg cm , where C is the sulfate concentration in the water and Cp is the sulfate concentration in the soil pore water. 

Estimated Diffusive Flux of Ammonium, Phosphate, and Sulfate as Influenced by Soil or Sediment Porosity 

Porosity ((p) Tortuosity Factor (0 ) Ammonium Flux (mg m day ) Phosphate Flux (mg m day ) Sulfate Flux (mg m day 

The dC/dx values are 3, 0.3, and -3 jg cm for ammonium, phosphate, and sulfate, respectively. Positive flux indicates upward diffusion from soil or sediment to overlying water column, whereas negative flux is from water column into soil or sediment. 

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In most of the 30 porewater profiles examined between 1984 and 1987, sulfate concentrations decreased to < 20 peq/L within 5 cm of the sediment-water interface and remained relatively constant below this depth. These data indicate that sulfate reduction occurs primarily in the upper 5 cm, a contention which is supported by results from laboratory studies in which 35SO was added to intact sediment-water cores. We generally observed steeper sulfate gradients in summer than in winter, and hypothesize that winter gradients are not as steep because microbial activity is reduced. So far, however, we have not found a statistically significant relationship between temperature and sulfate flux. 

For this reason Pb has been used as a tracer of the precipitation fate of S04. Turekian et al. (1989) used the S04 / Pb ratio in aerosols and the flux of °Pb measured in bucket collections to determine the SO flux across the Pacific Ocean. Further, they showed that the S04 / Pb in aerosols from regions of high biological productivity was higher than for normal relatively unpolluted air (Table 3) indicating a sulfate source from the oxidation of dimethyl sulfide (DMS). The measured flux of DMS from the oceans at the equator matched the biogenic flux determined from the °Pb calculation (Table 4). (Actually, as we shall see below, this concordance is probably due to an underestimate of sulfate flux and an overestimate of the fraction of DMS oxidized to sulfate.)... 

The coincidence of maxima in the methane oxidation rate and the sulfate reduction rate in Saanich Inlet strongly suggests that the methane oxidizing agent was sulfate, either via direct reaction, or coupled indirectly through reactions with other substrates (Devol, 1983). A methane-sulfate coupled reaction diffusion model was developed to describe the inverse relationship commonly observed between methane and sulfate concentrations in the pore waters of anoxic marine sediments. When fit to data from Saanich Inlet (B.C., Canada) and Skan Bay (Alaska), the model not only reproduces the observed methane and sulfate pore water concentration profiles but also accurately predicts the methane oxidation and sulfate reduction rates. In Saanich Inlet sediments, from 23 to 40% of the downward sulfate flux is consumed in methane oxidation while in Skan Bay this value is only about 12%. 

It should be indicated at this point as well that the calculated diffusive sulfate flux from the bottom water into the sediment, and from there into a depth of about 5.4 m, is the unequivocal consequence of the profile shown in Figure 3.6. It also follows that this sulfate is degraded in the depth of 5.4 m within a depth interval of at the most 10 to 20 cm thickness. The calculated Corg amount that undergoes conversion again depends on the assumption made by Froelich et al. (1979) that indeed the whole of sulfate reacts with organic carbon. Several studies demonstrated that this must... 

The sample calculations for ammonium, phosphate, and sulfate fluxes are shown as follows. 

Later the concentration of sulfate gradually increased in the seawater. Initially its concentration was too low to form anhydrite and all the sulfate entering the hydrothermal system got reduced. This formed a stabilizing buffer on the sulfate concentration in seawater because the sulfate flux into the oceanic crust was proportional to its concentration. 

It was also found that the direction of sulfate fluxes in or out of the cell depended on its intracellular pool. When sulfate-depleted cells were transferred to a new medium, they actively accumulated sulfate first, but then started to release it (Fig. 4.2). Cells grown first in the medium high in sulfate, when transferred to a fresh medium, started to release sulfate at once. Interestingly, such an oscillatory pattern of sulfate utilization was not a common property of all propionic acid bacteria. For instance, P. petersonii steadily took up sulfate from the medium, while the two closely related strains, P. shermanii and P. freudenreichii, showed an oscillatory pattern of sulfate consumption, like the distantly related E. coli (Fig. 4.3). 

David, M.B. and Mitchell, M.J. 1987. Transformations of organic and inorganic sulfur importance to sulfate flux in an Adirondack forest soil. J. Air... 

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