Denitrification fractionation effect

Small enrichments of stable isotopes can be used for detailed studies of specific processes such as denitrification. If these processes are important in the flux of material in the ecosystem from an isotopic mass-balance standpoint, then process rates and associated isotopic fractionations must be measured independently. Alternatively, sufficient isotope must be added to enrich the pool of interest to a level at which the magnitude of fractionation effects is negligible. For example, an enrichment of ammonium by 1 order... 

The main processes involved in the biologieal utilization of nitrogen are all associated with kinetic fractionation effects, nevertheless they exhibit different fractionation factors. The isotope effect of nitrogen fixation (a = 1.000 to 1.004) is small relative to the effects of bacterial nitrification, denitrification, or anammox (a = 1.02 to 1.04) (see Montoya et al. 1994 Table 1). The results by Miyake and Wada (1971) indicate that little overall isotope fractionation occurs in the... 

Microbial reduction of nitrate to N2, known as denitrification, is similar. It is kinetically inhibited in the absence of bacteria and is known to induce a kinetic isotope effect (Blackmer and Bremner 1977 Kohl and Shearer 1978 Mariotti et al. 1981 Bryan et al. 1983 Htibner 1986 Mariotti et al. 1988). W N shifts ranging from 6.5%o to 20%o have been observed experimentally. As with sulfate, microbial fractionations appear to depend on the metabolic states of the microbes. 

Bruchert V, Knoblauch C, Jorgensen BB (2001) Controls on stable sulfur isotope fractionation during bacterial sulfate reduction in Arctic sediments. Geochim Cosmochim Acta 65 763-776 Bryan BA, Shearer G, Skeeters JL, Kohl DH (1983) Variable expression of the nitrogen isotope effect associated with denitrification of nitrate. J Biol Chem 258 8613-8617 Canfield DE (2001) Biogeochemistry of sulfur isotopes. Rev Mineral Geochem 43 607-636 Chau YK, Riley JP (1965) The determination of selenium in sea water, silicates, and marine organisms. Anal Chim Acta 33 36-49... 

Because water-column denitrification occurs in the subsurface and because it consumes only a fraction of the nitrate plus nitrite available, its isotope effect is more completely expressed in the d N of subsurface nitrate. In denitrifying regions of the water column, the d N of nitrate in the subsurface is commonly elevated to 15%o or higher (Figure 8). The... 

Paul and Clark (11), pp. 147-158. Denitrification is also a particularly effective way of removing that fraction of fertilizer nitrogen that reaches estuary and shelf waters see Nixon, S. W., et al. 1996. The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean. Biogeochemistry 35 141-180. Dissolved nitrate in ground waters with low... 

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