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Denitrification, natural

Another Nr species emitted to the atmosphere, N2O, bears mention. Produced by nitrification and denitrification, natural emissions of N2O are —9.6TgNyr primarily from the oceans and tropical soils (Mosier et at, 1998). As compiled in... [Pg.4432]

Fig. 12-7. Fixation-denitrification cycle. Each arrow represents one flux. The magnitude of the flux is given in Tg N/yr. Where two numbers are given, the top value is the anthropogenic contribution and the lower number is the total flux (natural + anthropogenic). Fig. 12-7. Fixation-denitrification cycle. Each arrow represents one flux. The magnitude of the flux is given in Tg N/yr. Where two numbers are given, the top value is the anthropogenic contribution and the lower number is the total flux (natural + anthropogenic).
Sigman et al. [134] have described a bacterial method for measuring the isotopic composition of seawater nitrate at the natural-abundance level. The method is based on the analysis of nitrous oxide gas (N2O) produced quantitatively from nitrate by denitrifying bacteria. The classical denitrification pathway consists of the stepwise reduction of nitrate (NOp to nitrite (N02), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) ... [Pg.89]

Each of these steps is carried out by a dedicated enzyme encoded by a distinct gene. There is a rich literature on natural and genetically modified bacterial strains that lack discrete components of the denitrification pathway [ 140]. The... [Pg.89]

The maximum critical load for nitrogen acidity represents a case of no S deposition. The value of CLmaxN not only takes into account the nitrogen sinks summarized as CLminN, but consider also deposition-dependent denitrification as a denitrification fraction /de. Both sulfur and nitrogen contribute to acidification, but one equivalent of S contributes, in general, more to excess acidity than one equivalent of N, since nitrogen is also an important nutrient, which is deficient in the most natural ecosystems. [Pg.54]

The global ocean balance between N2 fixation and the loss of fixed nitrogen through anammox and denitrification. Source From Arrigo, K. R. (2005). Nature 437, 349-351. [Pg.690]

Given all these uncertainties, it is not currently possible to determine whether the nitrogen and/or phosphorus cycles are in a steady state. Indeed, anthropogenic inputs of both are now so large that the maintenance of a steady state seems unlikely. As noted earlier, natural deviations from a steady state in the nitrogen cycle are also deemed likely given the large spatial separation between the locales where denitrification and BNF take place. [Pg.699]

In the case of nitrogen, some is transferred to the atmosphere as a consequence of denitrification, which takes place in soils, sewage treatment plants, and natural waters. Some nitrogen is also volatilized as ammonia from animal feedlots. [Pg.784]

There are also significant natural sources of oxides of nitrogen, in particular nitric oxide, which is produced by biomass burning as well as by soils where nitrification, denitrification, and the decomposition of nitrite (N02) contribute to NO production. Figure 2.4b, for example, shows the relative emission rates for biogenically produced NO in the United States in 1990 (EPA, 1995). [Pg.17]

In short, the overall features of the chemistry involved with the massive destruction of ozone and formation of the ozone hole are now reasonably well understood and include as a key component heterogeneous reactions on the surfaces of polar stratospheric clouds and aerosols. However, there remain a number of questions relating to the details of the chemistry, including the microphysics of dehydration and denitrification, the kinetics and photochemistry of some of the C10x and BrOx species, and the nature of PSCs under various conditions. PSCs and aerosols, and their role in halogen and NOx chemistry, are discussed in more detail in the following section. [Pg.680]

Nitrous oxide is important not only as a greenhouse gas but, as discussed in Chapter 12, as the major natural source of NC/ in the stratosphere, where it is transported due to its long tropospheric lifetime (Crutzen, 1970). The major sources of N20 are nitrification and denitrification in soils and aquatic systems, with smaller amounts directly from anthropogenic processes such as sewage treatment and fossil fuel combustion (e.g., see Delwiche, 1981 Khalil and Rasmussen, 1992 Williams et al., 1992 Nevison et al., 1995, 1996 Prasad, 1994, 1997 Bouwman and Taylor, 1996 and Prasad et al., 1997). The use of fertilizers increases N20 emissions. For pastures at least, soil water content at the time of fertilization appears to be an important factor in determining emissions of N20 (and NO) (Veldkamp et al., 1998). [Pg.779]

Ammonia is oxidized in nature to nitrate via several intermediates in the process of nitrification. Nitrate may be reduced to nitrite by either a dissimilatory or an assimilatory process. Nitrite may be assimilated into the cell via reduction to ammonia, or it may be reduced by microorganisms to N20 and N2 in denitrification. A major part of the total nitrogen in this pathway is lost to the atmosphere. However, in turn, atmospheric dinitrogen is converted to ammonia by various bacteria in nitrogen fixation. [Pg.717]


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