Organic carbon oxidation-reduction balance

The values for the organism yield constants are assumed to be somewhat higher than for acetic acid since they are expressed on a molar basis and more than one species may participate in the reaction. The yield constants for carbon dioxide and methane are developed from the oxidation-reduction balances. 

By constraining the fraction of the total FeS that is from SO4- reduction based on isotope mass balance, the amount of CO2 produced from respiration of Fe3+ can then be calculated from the remaining portion of the total organic carbon oxidized. 

It is also often taken for granted that many of the Earth s subsystems are exposed to free oxygen (O2), leading to a range of one-way reactions of reduced materials (such as organic carbon or metal sulfides) to an oxidized form. As pointed out many times in earlier chapters, the oxidation-reduction status of the planet is the consequence of the dynamic interactions of biogeochemical cycles. As is the case with the acid-base balances, there is considerable sensitivity to perturbations of "redox" conditions, sometimes dramatically as in the case of bodies of water that suddenly become anaerobic because of eutrophication. Another extreme... 

The EOI of organic species appears, at first glance, to have little to do with metal removal from effluents. That is until one considers that for every electro-oxidation/reduction of a metal there must be a respective electro-reduction/oxidation of another species to maintain a charge balance. In many cases the other species is an organic molecule which can be easily oxidised/reduced phenols are examples. Phenols are oxidised to benzoquinones and catechols (scheme 14.5) which themselves can be oxidised to water and carbon dioxide. 

On a time series of Quaternary marine terraces in northern California, Brimhall et al. (1992) conducted the first mass balance analysis of soil formation over geologic time spans. This analysis provided quantitative data on well-known qualitative observations of soil formation (i) the earliest stages of soil formation (on timescales of 10 -10 yr) are visually characterized by loss of sedimentary/rock structure, the accumulation of roots and organic matter, and the reduction of bulk density and (ii) the later stages of soil development (>10 yr) are characterized by the accumulation of weathering products (iron oxides, silicate clays, and carbonates) and the loss of many products of weathering. 

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