Nitrogen isotopic fractionation process

Figure 34.3 Nitrogen isotopic fractionation processes. The vectors approximate the isotopic changes associated with the indicated addition or removal of nitrogen from an initial nitrate pool with a of 5%o (black filled circle). Note that the fractionating processes (water column deni-...

Wada, E. (1980) Nitrogen isotope fractionation and its significance in biogeochemical processes occurring in marine environments. In Isotope Marine Chemistry (Goldberg, E.D., Horibe, Y., and Saruhashi, K., eds.), pp. 375-398, Uchida Rokakudo, Tokyo. 

This phenomenon forms the basis for the formulations of Urey (1947) and Bigeleisen and Mayer (1947) for the temperature dependence of isotopic exchange between two molecules. With the nearly simultaneous development of the isotope-ratio mass spectrometer by Nier et al. (1947), the potential for application of stable isotopes was created. Other isotopic fractionation processes are observed in kinetics, diffusion, evaporation-condensation, crystallization, and biology (e.g., photosynthesis, respiration, nitrogen fixation, sulfate reduction, and transpiration). The concomitant isotopic fractionations can also be used to provide details of the relevant process. 

Stable isotopes of each of these elements have played important roles in elucidation of their chemistries. Specifically, and have been used as stable tracers for research on N-chemistry dealing with food and fiber production, metabolic pathways, and environmental control. Their value is ultimately limited because macroscopic amounts of carrier often exceed in situ concentrations (and therefore influence the biochemistry), and natural nitrogen isotope fractionation leads to variances in natural abundance. Nevertheless, stable tracers have been used effectively in many studies, including foflowing N-cycle processes in soils (1) and unraveling metabolic pathways (2,3). 

Various isotope effects are the ultimate cause of natural variations in the distribution of the stable isotopes of nitrogen. There are two types of isotope effect (i) physical, and (ii) chemical. Physical effects are associated with processes such as freezing/melting, evap-oration/condensation, adsorbtion, diffusion, etc chemical effects occur in both inorganic and biochemical reactions and are the dominant reason for observed N-isotopic variations in living and sedimentary OM. Isotope effects are manifest as differences in the relative distribution of N and N between reactants and products, the result of such changes is commonly referred to as isotope fractionation. Processes like those outlined above typically have a characteristic fractionation associated with the reaction. The fundamental cause of the... 

The most abundant isotope is which constitutes almost 99% of the carbon in nature. About 1% of the carbon atoms are There are, however, small but significant differences in the relative abundance of the carbon isotopes in different carbon reservoirs. The differences in isotopic composition have proven to be an important tool when estimating exchange rates between the reservoirs. Isotopic variations are caused by fractionation processes (discussed below) and, for C, radioactive decay. Formation of takes place only in the upper atmosphere where neutrons generated by cosmic radiation react with nitrogen ... 

Mariotti, A., Germon, J.C., Hubert, P., Kaiser, R, Letolle, R., Tardieux, A. and Tardieux, P. 1981 Experimental determination of nitrogen kinetic isotope fractionation some principles illustration for the denitrification and nitrification processes. Plant and Soil 62 413-430. 

Santruckova H, Bird MI, Lloyd J (2000) Microbial processes and carbon-isotope fractionation in tropical and temperate grassland soils. Funct Ecol 14 108-114 Sisti CPJ, Dos Santos HP, Kohhann R, Alves BJR, Urquiaga S, Boddey RM (2004) Change in carbon and nitrogen stocks in soil under 13 years of conventional or zero tillage in Southern Brazil. Soil Fill Res 76 39-58... 

The complex biochemical paths in organisms offer many ways to fractionate isotopes by both kinetic and equilibrium processes. It is therefore expected, and is observed, that the different carbon, hydrogen, oxygen and nitrogen atoms in organic residues show compound and atom-site specific isotope fractionations... 

In recent years, tremendous progress has been achieved in the analysis of the isotope composition of important trace compounds in the atmosphere. The major elements - nitrogen, oxygen, carbon - continually break apart and recombine in a multitude of photochemical reactions, which have the potential to produce isotope fractionations (Kaye 1987). Isotope analysis is increasingly employed in studies of the cycles of atmospheric trace gases e.g., CH4 and N2O, which can give insights into sources and sinks and transport processes of these compounds. The rationale is that various sources have characteristic isotope ratios and that sink processes are accompanied by isotope fractionation. 

Fractional distillation of NO is an effective method for concentrating N. Chemical exchange processes for nitrogen isotope separation include the following ... 

It appears that FTT reactions can account reasonably well for most features of organic matter in meteorites. The only alternative process, the Miller-Urey synthesis, fails to account for the aliphatic and aromatic hydrocarbons, nitrogen heterocyclics, many oxygen compounds, the polymer, and carbon isotope fractionations, though it remains an alternative and perhaps superior source of amino acids and may, in an extended sense, be responsible for the deuterium enrichments. 

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