Coupled geochemical cycle

Fig. 10.1. Extension of Salomons (1993) concept of coupled geochemical cycles...

Coupled Geochemical Cycle Sulfur-Carbon-Oxygen (S-C-O) Cycle... 

In Chap. 5, fundamental equations on geochemical cycle and examples of global carbon and other (S, Sr) cycles and climate change deduced from the global carlxMi cycle simulations are presented. However, recent investigatiOTis of coupled geochemical cycles (C, S, Sr, O etc) are not described. 

Tajika, E. (1992) Evolution of the atmosphere and ocean of the Earth global geochemical cycles of C,H,0,N, and S, and degassing history coupled with thermal history. Doctoral Thesis, University Tokyo, 416 pp. 

Selenium, in the form of selenate or selenite, is toxic to D. desulfuricans (Tomei et al. 1995) and Wolinella succinogenes (Tomei et al. 1992) at elevated levels. At sublethal levels of 0.1-1. OmM selenite or 10 mM selenate, minimal levels of growth is observed with both D. desulfuricans and Wolinella succinogenes. With both selenate and selenite, colloidal elemental selenium (Se°) is produced inside the cell and released into the culture fluid after cell death. This reduction of Se(VI) and Se(IV) by these anaerobes is not coupled to growth and proceeds by mechanisms that have not yet been identified. Selenite and selenate reduction with formation of elemental selenium by these nonrespiratory processes serve to detoxify the environment for future bacteria and may be important for the geochemical cycle of selenium. 

Fig. lb). Iron and manganese particles often accumulate at redox boundaries (Davison, 1985 De Vitre et al., 1988) and supply reactive mineral surfaces in zones with high chemical electron fluxes. Oxidation-reduction reactions of metal ions at mineral surfaces thus play a key role in the geochemical cycling of electrons . The distribution and fate of many inorganic species is coupled with the reductive dissolution and the oxidative precipitation of manganese and iron at redox boundaries. 

The organometallic chemistry of molybdenum has been reviewed and papers published in 1971 dealing with this area of chemistry for molybdenum and tungsten have been surveyed. " Reviews discussing aspects of catalysis by tungsten compounds and the geochemical cycle of molybdenum in the environment have been published. Coupled proton-electron transfer mechanisms have been proposed for the action of molybdenum in several enzymes to explain many experimental observations. ... 

The conceptual approach of "storage capacity-controlling properties" forms the link between the geochemical cycles comprising driving forces such as organic matter/redox-sensitive elements and cycles of mobilizable micropollutants. This concept of coupled cycles has been designed by Salomons (1993 Fig. 10.1). 

Geochemical cycle of each element interrelates. During recent years, large number of coupling geochemical modeling have been carried out (Kashiwagi et al. 2008 etc.). 

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