Nitrification rates

Noncorrosive materials should be used for the dosing equipment. The addition of iron salts also reduces the alkalinity of the wastewater, i.e., it may decrease the pH value. An effect of a low alkalinity of wastewater is a potential reduction of the nitrification rate in the subsequent treatment process. 

Burger M, Jackson LE (2003) Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates in organic and conventional cropping systems. Soil Biol Biochem 35 29-36... 

The pattern of NH4+ and N03 concentrations, and net mineralization and net nitrification rates in soils before and after clearing and burning tropical forest indicate ... 

Table 5. Inorganic N concentrations, mineralization and nitrification rates, and turnover rates ofNH% and NOJ in a chronosequence before and after forest clearing at Nova Vida, Brazil (after Neill et al., 1999).

For the first and second biological nitrification rate steps, the reaction kinetics for any stage n are given by... 

In suboxic waters, a secondary ammonium maximum can also be present. It typically lies just above the secondary nitrite maximum. This secondary maximum is supported by high rates of ammonification. Because the waters are suboxic, nitrification rates are slow permitting the buildup of ammonium. 

Nitrification is limited in most soils by the supply rate of NH4+ (40, 41). Competition exists between nitrifiers and vegetation, which may both be limited by the availability of NH4 +. This microbial demand for NH4 +, coupled with the high cation-exchange capacity of most temperate forest soils, leads to surface-water NH4+ concentrations that are usually undetectable. Nitrification rates may also be limited by inadequate microbial populations, lack of water, allelopathic effects (toxic effects produced by inhibitors manufactured by vegetation), or by low soil pH. 

The overall nitrification rate which describes conversion of NH to NO can be expressed by... 

Urea undergoes microbial hydrolysis catalyzed by urease, leading to loss of as much as 30% of its nitrogen from ammonia volatilization. The reduced nitrogen availability in the soils appears particularly when urea is surface broadcast on soils. The factors that influence ammonia volatilization include levels of urease activity, moisture availability, nitrification rate, and soil texture (Bernard et al., 2009). 

Medina and Cuevas (1994) analyzed available data for potential mineralizaton of nitrogen and nitrification rates from tropical forests. Nitrogen mineralization rates in... 

Amazon terra firme forests are lower than those measured on richer soUs in Costa Rica and Barro Colorado, Panama. In general all the organic N mineralized is subsequently nitrified, leaving little or no free NH4. Under natural conditions, however, NH4 could be incorporated into biomass, immobilized in the soil, or taken up by the vegetation, resulting in a reduction of nitrification rates. 

Montagnini, F., and R. Buschbacher. 1989. Nitrification rates in two undisturbed tropical rain forest and three slash-and-burn sites of the Venezuelan Amazon." Biotropica 21 9-14. 

Five depth profiles of NO and the corresponding NO production rates have been measured in the ETNP (Ward and Zafiriou, 1988) NO concentrations were in the range from 0 up to 65 pmol At four stations located in the open ocean, maximum NO concentrations were observed at the upper boundary of the oxygen minimum zone (OMZ, O2<10 pmol L ), whereas one coastal station showed an increase of NO from Opmol at the surface to about 20 pmol at the bottom in about 250m. Maximum NO production rates were found at the upper boundary of the OMZ at the open ocean stations. However, Ward and Zafiriou (1988) could not unambiguously identify the NO formation process because NO production rates and nitrification rates (i.e., NH oxidation rates) were not correlated. NO accumulation appeared when O2 concentrations were lower than 100 pmol L , whereas in the core of the OMZ with O2 concentrations close to 0 pmol denitrification seemed to cause a rapid turnover of NO. Highest ever-reported concentrations of dissolved NO were found off Peru ranging from 0 up to 400 pmol (Zafiriou, personal communication in Ward and Zafiriou (1988)). 

More simultaneous measurements of NH3 in the ocean and in the atmosphere are needed to reduce the considerable uncertainties of the ocean/atmosphere flux estimates. The ongoing acidification of the ocean will shift the NH3/NH4 equilibrium to NH. On the one hand this might have implication for the atmospheric distribution of NH3, since the uptake capacity of the ocean will be increased with unknown consequences for chemistry of the atmosphere (e.g. the aerosol formation) over the ocean. On the other hand this might have severe implications for the nitrification rates in seawater because they are influenced by the pH. When the pH drops from 8 to 7, nitrification rates can be reduced by 50% (Huesemann et al., 2002). (One explanation for this is that the ammonia monooxygenase enzyme uses rather NH3 than NH4 as substrate.) Most recently it was suggested that atmospheric NH3 serves as a foraging cue for seabirds such as the blue petrel (Nevitt ei a/., 2006) is an excretion product of... 

Methods for measuring nitrification rates in water and sediments 216... 

Environmental Variables Affecting Nitrification Rates and Distributions 234... 

Heterotrophic nitrification has been studied in terrestrial systems, especially acid forest soils, where it has been difficult to document autotrophic nitrification. Experiments using isotopes to differentiate production of N03 from inorganic and organic substrates in a forest system found that heterotrophic nitrification accounted for less than 10% of the total nitrification rate (Barraclough and Puri, 1995). No information of this sort is available on the occurrence or significance of heterotrophic nitrification in aquatic systems. The potential for NH3 and N02 oxidation by heterotrophic bacteria in aquatic systems warrants further exploration, and the capability may be present in many strains already in culture. If heterotrophic nitrification is common in nature, then a focus on autotrophic nitrification as the... 

As with most biogeochemicaUy important processes, there is no perfect method for direct measurement of nitrification rates. Potential artifacts arise from the use of incubations, but incubation free methods can also be problematic. 

To overcome the bias resulting from uneven dispersal of tracer or inhibitor, sediment rate measurements are often made in slurries, which destroy the gradient structure of sediments, which is essential to the in situ fluxes. Slurries may provide useful information on potential rates, but not in situ rates. Potential nitrification rates and rates measured in intact cores were not correlated in estuarine sediments (Caffrey et ah, 2003). The lack of correlation was explained by the inclusion of variable amounts of anoxic sediments in the slurries from which the potential rates were derived. 

The direct radioisotope tracer method, in which the accumulation of radiolabeled product from added radiolabeled substrate over time yields a rate estimate, is not very practical for measuring rates of nitrification in the environment. Capone et al. (1990) were able to quantify nitrification rates using but the isotope is so shortlived (10 min half-life) that its use is usually impractical. 

The approach is most useful in water samples because complete mixing of the tracer is possible. In sediments, rate measurements are constrained by the inhomogeneous nature of the sample and the dependence of rates on the structure of the environment. In this situation, fluxes between overlying water and sediment cores can be analyzed to obtain areal rates. In conjunction with tracer addition, estimates of nitrification rates can be obtained from the dilution ofN02 or N03 in the overlying water due to its production in the sediments (Capone et ai, 1992). The isotope pairing method for measurement of denitrification (Nielsen, 1992 Rysgaard et ai, 1993) is essentially an isotope dilution approach from which both nitrification and denitrification rates can be calculated. 

Nitrification rates in oxygenated water columns show typical depth distributions with maximum rates near the bottom of the euphotic zone and a rapidly declining rate with increasing depth below that. 

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