Nitrate reduction reductant, sources

Biodegradation of fuel oils in sediments is inhibited under anaerobic conditions (Bartha and Atlas 1977). Under anaerobic conditions, some soil microorganisms are capable of nitrate reduction using fuel oils as the carbon source, although nitrite may be an unwanted by-product. However, the addition of a small amount of oxygen (0.2 volume percent oxygen) to the medium can accelerate the degradation of the oil without the concomitant production of nitrite (Riss and Schweisfurth 1987). 

Practical considerations and implementation. Most investigations involve the use of distilled/deionised water with KNO3 as the nitrate ion source thereby avoiding any potential impact of water hardness and dissolved salts on the catalytic removal of nitrates. It has been pointed out that in the presence of anions such as S04 and bicarbonates, which may be present in tap-water at concentrations of above 90 ppm, reduced nitrate reduction rates are to be expected as a result of competitive anion adsorption. Pintar and co-workers have indicated that nitrate removal rates are reduced when using drinking water as opposed to distilled water. Chloride ion is known to reduce the rate of nitrate removal while the choice of cation as counter ion influences the rate in the order, < Na < Ca < Mg + <... 

Figure 16.2 The redox intermediate, nitrite (N02 ), occupies a central position in the marine N-cycle. Shown are the various processes that are either sources or sinks for N02. Abbreviations include (clockwise from top) ANR = assimilatory nitrate reduction, Nit = nitrification, photolysis = UV-driven photocatalysis, DNR/DN = dissimilatory nitrate reduction/denitrification, ANR and Nit = as above, Anammox = Anaerobic ammonium oxidation.

Several comprehensive studies of N assimilation in the North Pacific trades biome have been conducted over the past several decades. Gundersen and his colleagues (1974, 1976) were the first to estabhsh N2 fixation as a source of new N to the open ocean ecosystem, and concluded that it was a more important source of fixed N than wet deposition from the atmosphere (see Case Studies section). They also made measurements of the rates of nitrification, denitrification and assimilatory nitrate-reduction. These latter experiments involved the addition of fairly high concentrations of exogenous N substrates (NH4 , N02, NOa ) and extended incubations (days to months), so the rates reported must be viewed as potential rates at best. 

Welsh, D. T., CastadeUi, G., Bartoli, M., Poli, D., Careri, M., de Wit, R., and Viaroh, P. (2001). Denitrification in an intertidal seagrass meadow, a comparison of N-isotope and acetylene-block techniques DissimUatory nitrate reduction to ammonia as a source of N2O Mar. Biol. 139, 1029-1036. 

Ammonia. The greatest amounts of ammonia enter into the atmosphere during the biological decomposition of organic matter and in the reduction of nitrites and/or nitrates. The anthropogenic sources are lower by several... 

The nitrate reduction is an important process, since it facilitates the entrance of NO3 into the plant metabolism. The resorbed ammonia nitrogen, urea nitrogen and amino acids can be easily utilized by the plants. Nitrates accepted are used for the synthesis of nitrogen-containing organic substances only after their reduction to ammonia. This reduction is sensitive to the environmental conditions. In the case of a lack of saccharides as energy sources, or if the activity of the reductases is lessened, nitrate nitrogen can be accumulated in plant tissues. 

Another mechanism of fixed N loss that occurs in sediments and the water column is anaerobic ammonium oxidation, or anammox , in which nitrite (from nitrate reduction or ammonium oxidation) is used to oxidize ammonium to N2 (N02 + Nl-l4+ N2+ 2H2O). This process has unknown effects on isotope distributions in the ocean. The effects of anammox on N isotopes must depend on the organism-scale isotope effects, the sources of nitrite and ammonium substrates for the reaction, and the degree to which these substrates are consumed. For instance, if nitrate reduction by denitrifiers is the source of the nitrite, remineralization processes are the source of the ammonium, and both the nitrite and ammonium are completely consumed in the environment where anammox occurs, then the isotope discrimination would simplify to that of the nitrate reduction by denitrifiers averaged with any isotope discrimination during the remineralization that produces the needed ammonium. It should be noted that many water-column-derived... 

Heterotrophic bacteria require the presence of an organic carbon source. Methanol proved to be the most suitable for giving maximal rate of nitrate reduction. The optimal methanolinitrate ratio is 2.A7 (g/g), which corresponds to a C N mole ratio of 1 (1). 

In wetlands, nitrate is used by microbes and plants as a nitrogen source or as an electron acceptor to support catabolic activities of select heterotrophic bacteria. As early as 1882, Maquenne reported the following observations on nitrate reduction in soils ... 

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