Organic matter manganese reduction

Soil pH affects the transformation of Cr between Cr(III) and Cr(VI) in soils. Since Cr(VI) has greater bioavailability and mobility in soils than Cr(III), which is strongly bound by soil solid matrix (Han and Banin, 1997). Cr(III) can be oxidized by soil manganese oxides into Cr(VI), while Cr(VI) can be reduced by organic matter, Fe(II) and microorganisms in soils. Reduction of Cr(VI) has been found to occur much slower in alkaline soils compared to acid soils (Cary et al., 1997). 

A few examples of chemoautolithotrophic processes have been mentioned in this chapter, namely anaerobic methane oxidation coupled to sulfate reduction and the ones listed in Table 12.2 involving manganese, iron, and nitrogen. Another example are the microbial metabolisms that rely on sulfide oxidation. Since sulfide oxidation is a source of electrons, it is a likely source of energy that could be driving denitrification, and manganese and iron reduction where organic matter is scarce. 

Canfield, D.E., Thamdrup, B., and Hansen, J.W. (1993) The anaerobic degradation of organic matter in Danish coastal sediments iron reduction, manganese reduction, and sulfate reduction. Geochim. Cosmochim. Acta 57, 3867-3883. 

Anoxic NH3 oxidation, whether it results directly in N2 formation (as in anammox) or in NOs production (when linked to manganese reduction), would introduce new links into the aquatic and sediment N cycle. Failure to account for anoxic NH3 oxidation might lead to an underestimate of NH4+ removal, because the products do not accumulate they are either lost to the atmosphere immediately, or rapidly reduced by the next step in the anaerobic cychng of organic matter. 

Okita P. M., Maynard J. B., Spiker E. C., and Force E. R. (1988) Isotopic evidence for organic matter oxidation by manganese reduction in the formation of stratiform manganese carbonate ore. Geochim. Cosmochim. Acta 52, 2679-2685. 

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