Sulfur cycle organisms

Anaerobic processes in wastewater of sewer systems in terms of both the organic matter transformations and the sulfur cycle have been dealt with in Chapter 6. Particularly, Section 6.4 has focused on the integrated aerobic-anaerobic sewer process model. From a conceptual point of view, the anaerobic... 

As far as organic matter transformations are concerned, the process rates are significantly slower compared with aerobic transformations. Basically, readily biodegradable organic matter is preserved and even, to some extent, produced opposite to the situation when aerobic processes proceed. The sulfur cycle, until now included in the sewer process model, is relatively simply described following empirical expressions for sulfide formation. Other important processes in this respect, e.g., hydrogen sulfide emission and sulfide oxidation, still need to be included, however, and, most of all, investigated from a conceptual point of view. 

Both inorganic and organic transformations are important in the sulfur cycle in Forest ecosystems. The major sulfur pools and transformation processes are shown in Figure 4. 

Kinetic isotope effects during microbial processes. Micro-organisms have long been known to fractionate isotopes during their sulfur metabolism, particularly during dissimilatory sulfate reduction, which produces the largest fractionations in the sulfur cycle... 

The surface part of the sulfur cycle is connected with the functioning of the atmosphere-vegetation-soil system. Plants adsorb sulfur from the atmosphere in the form of S02 (fluxes C7 and C22) and assimilate sulfur from the soil in the form of SO4 (flux C15). In the hierarchy of soil processes, two levels can be selected defining the sulfur reservoirs as dead organics and S04 in soil . The transitions between them are described by flux C16 = b2STL, where the coefficient b2 = b2, b2 2 reflects the rate b2 of transition of sulfur contained in dead organics into the form assimilated by vegetation The coefficient b2>2 indicates the content of sulfur in dead plants. 

It is also possible that bacterial decomposition of sulfur containing organic compounds may account for some DMS in natural waters (31-36). Conversely, bacteria may also utilize DMS and therefore act as a sink (37-39). The contribution of bacterial processes to the DMS/DMSP cycle in open ocean environments has not been addressed and is as yet not understood. However, studies to better understand the biogeochemistry of DMS can not exclude bacterial processes (e.g. 4041). 

Luther III, G.W., Church, T.M., Scudlark, J.R., and Cosman, M. (1986) Inorganic and organic sulfur cycling in salt-marsh pore waters. Science 232, 746-779. 

Heterotrophic respiration fueled by the rain of organic matter from the surface ocean is ubiquitous in marine sediments. Its rate determines one of the important characteristics of the sedimentary environment the depth of redox horizons below the sediment-water interface. Heterotrophic respiration is the process by which carbon and nutrients are returned to the water column it is important in the marine fixed nitrogen and sulfur cycles and the accumulation of metabolic products sets the conditions for the removal of phosphorus from the oceans in authigenic minerals. A great deal of effort has been directed toward quantifying the rates, pathways, and effects of metabolism in sediments. 

In addition, the report by Smock et al (1998) that when thiosulfate is used as the oxidant (instead of sulfate), the fractionation of sulfur is much lower (on the order of 15 per mil), reminds us of two critical items. First, there are many organisms now in culture that contribute to the sulfur cycle, and many of them (and their various chemistries) are not well characterized with regard to sulfur fractionation. Perhaps it would be wise to revisit the fractionation that occurs with the oxidation of various sulfur species, both photosynthetic and nonphotosynthetic. Second, we are reminded that many of the organisms that contribute to the environment today have not been grown in culture. 

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