Reaction with sedimentary organic matter

The pathways for sedimentary microbial metabolism are outlined in Table 2. They are presented in order of decreasing free energy yield for reaction of each oxidant (shown in bold type in the table) with sedimentary organic matter (Froelich et ai, 1979). Pore-water data support the assertion that the electron acceptors are used in this order of decreasing free energy yield. The order of the NO N2 and Mn02 Mn(II) reactions is uncertain, however, and examples exist in the literature for which Mn(IV) appears to be used before NO )" (Froelich et al., 1979 Klinkhammer, 1980) or for which NO appears to be used first (e.g., Shaw et al., 1990 Lohse et al., 1998). Thus, the order of electron acceptor use is O2, NO ... 

Pyrite is a major sink for reduced sulfur from the JH S/S0/]- system to the extent that reactive iron is available. In sediments with limited amounts of reactive iron, reduced sulfur species in the H2S/S°/H2SX system are available for reaction with the sedimentary organic matter. 

In the environment. More generally, the results imply that a major chemical pathway for the Incorporation of sulfur into organic geopolymers is by reaction of HS with reactive sites, e.g. oleflnlc double bonds, displaceable halogens (39). within sedimentary organic matter. The Michael addition reaction of HS to acrylic acid may be used as a model case of such interactions. 

Many such studies of sedimentary phosphorus profiles, also incorporating pore water measurement of soluble reactive phosphate, have demonstrated that redox-controlled dissolution of iron (hydr)oxides under reducing conditions at depth releases orthophosphate to solution. This then diffuses upwards (and downwards) from the pore water maximum to be re-adsorbed or co-precipitated with oxidized Fe in near-surface oxic sections. The downwards decrease in solid phase organic phosphorus indicates increasing release of phosphorus from deposited organic matter with depth, some of which will become associated with hydrous iron and other metal oxides, added to the pool of mobile phosphorus in pore water or contribute to soluble unreactive phosphorus . The characteristic reactions involving inorganic phosphorus in the sediments of Toolik Lake, Alaska, are shown in... 

However, I2 and HOI are the likely intermediates formed by both abiotic and biotic processes during L oxidation. These intermediates, if formed, can be reduced back to I react with organic matter to form particulate or dissolved organic iodine (RI) compounds or be volatilized to the atmosphere as I2, HOI, or CH3I. Iodate can also react directly with humic material during reduction to form RI (58), but this reaction is more important in sedimentary environments and has not been documented in the photic zone. 

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