High Nitrification Rates Research Articles

Simultaneous Nitrification and Denitrification in Aerobic Chemostat Cultures of Thiosphaera pantotropha

Thiosphaera pantotropha is capable of simultaneous heterotrophic nitrification and aerobic denitrification. Consequently, its nitrification potential could not be judged from nitrite accumulation, but was estimated from complete nitrogen balances. The maximum rate of nitrification obtained during these experiments was 93.9 nmol min mg of protein. The nitrification rate could be reduced by the provision of nitrate, nitrite, or thiosulfate to the culture medium. Both nitrification and denitrification increased as the dissolved oxygen concentration fell, until a critical level was reached at approximately 25% of air saturation. At this point, the rate of (aerobic) denitrification was equivalent to the anaerobic rate. At this dissolved oxygen concentration, the combined nitrification and denitrification was such that cultures receiving ammonium as their sole source of nitrogen appeared to become oxygen limited and the nitrification rate fell. It appeared that, under carbon-and energy-limited conditions, a high nitrification rate was correlated with a reduced biomass yield. To facilitate experimental design, a working hypothesis for the mechanism behind nitrification and denitrification by T. pantotropha was formulated. This involved the basic assumption that this species has a "bottleneck" in its cytochrome chain to oxygen and that denitrification and nitrification are used to overcome this. The nitrification potential of other heterotrophic nitrifiers has been reconsidered. Several species considered to be "poor" nitrifiers also simultaneously nitrify and denitrify, thus giving a falsely low nitrification potential.

Nitrogen Transformations in Lake Ontario

Concentrations of ammonium plus nitrite in Lake Ontario were highly correlated with ammonium regeneration from zooplankton excretion (r = 0.966), inferring that elevated nitrite concentrations result from nitrification. Nitrapyrin-sensitive dark 14C-labeled bicarbonate assays confirmed high rates of nitrification by chemoautotrophic bacteria. 15N-labeled nitrate experiments showed that nitrate, not ammonium, was the principal form of N used for total microbial protein synthesis. Size fractionation experiments also suggested that small cells were responsible for most of the ammonium uptake, while large cells used mostly nitrate. Nitrate depletion in the surface waters during summer stratification resulted from movement to particulate N, nitrite, and ammonium as well as losses in particulate N due to sedimentation. At least one third, however, was unaccounted for (i.e. 30 mg N∙m−2∙d−1) and may have been converted to protein which would move up the food chain to larger organisms (e.g. fish) not sampled during conventional water chemistry. Nitrous oxide profiles showed that nitrate losses through denitrification are unlikely to occur. Consequently, unless nitrate loading to Lake Ontario is reduced, nitrate concentrations should be expected to continue to increase.

Nitrification and sulphur oxidation by Aspergillus flavus growing in medium containing reduced nitrogen and sulphur

Aspergillus flavus oxidized elemental sulphur in vitro to thiosulphate, tetrathionate and sulphate, and mineralized peptone oxidizing the liberated ammonium to nitrite and nitrate. When elemental sulphur was added to peptone-containing medium the fungus oxidized sulphur but its ability to nitrify was inhibited. Such inhibition could have resulted from the reduction in medium pH following S-oxidation. Nitrification was still inhibited however, when S-oxidation occurred in medium buffered to pH 7.0, which suggests that pH was not the only factor inhibiting nitrification. Thiosulphate inhibited nitrification by A. flavus at concentrations similar to that produced by the fungus when oxidizing sulphur. Higher rates of nitrification by A. flavus occurred in medium containing ammonium sulphate and acetate, and in this medium thiosulphate (100 μg ml−1) prevented nitrification by A. flavus for one week, and reduced the rate of nitrification after three weeks. A. flavus appears to be incapable of simultaneously nitrifying and oxidizing sulphur due to the inhibitory effect of thiosulphate.

The effect of five years acid treatment on leaching, soil chemistry and weathering of a humo-ferric podzol

This paper describes the effect of treating a nutrient-poor forest soil in monolith lysimeters with H2SO 4, pH 3.0, for 4.75 yr. The lysimeters were instrumented with porous cup probes to distinguish processes occurring in each soil horizon. In the A horizon base cation exchange and sulphate absorption were the principal proton- consuming processes whereas lower down the profile Al3+ dissolution from hydrous oxides dominated. Acid treatment thus reduced the amount of amorphous Al in the lower horizons, but exchangeable Al was unaffected. Sulphate absorbtion was positively correlated with the distribution of Al hydrous oxides. High rates of nitrification reduced the differences between acid and control monoliths, but acid treatment significantly reduced soil pH down to 75 cm and reduced the levels of exchangeable base cations in the litter and A horizons. Acid treatment increased the leaching rates of base cations and Al. Consideration of the total base cation content shows that acid treatment increased the rate of weathering by 0.7–1.4 k eq ha−1 yr−1. The results should be useful in modelling more realistic rates of acid input to similar soils.

Microclimatic controls of nitrogen mineralization and nitrification in shortgrass steppe soils

The depth distributions of rates of net nitrogen mineralization and nitrification were measured in a series of field and laboratory incubations. Field studies suggested that the highest rates of mineralization and nitrification occurred in the surface 2.5 cm such that forty to sixty percent of the N mineralization in 20-cm soil column occurred in the surface 2.5cm. Some upward nitrate movement occurred but laboratory studies suggested that surface rates were not an artifact of nitrate mobility alone. Microclimatic data indicate that either dew or upward movement and condensation of soil water vapor may drive biological activity at the soil surface. High rates of N mineralization even in dry horizons were sustained as long as water was stored within the 0-to 20-cm depth. High rates of nitrification were found in all incubations, and field measurements showed NO3− to be the predominant form of inorganic N, despite previous characterization of the shortgrass steppe as an NH4+-dominated system.

Simultaneous estimation of several nitrogen cycle rates using 15N: Theory and application

Principles of isotope dilution, modeling, and nonlinear parameter estimation were used to simultaneously determine N cycle rates. Analysis of the sensitivity coefficients for the models used in this study demonstrated that the four parameters of interest—the rates or rate constants of mineralization, immobilization, nitrification, and denitrification—were estimable. This analysis also illustrated which sampling design would be best for the experiments performed.We found that both zero- and first-order models could describe N cycling, with the first-order model being more generally appropriate. The estimates obtained for mineralization, immobilization, and nitrification had relatively small standard errors; however, denitrification parameters were poorly estimated. This is due in part to the much lower rate of denitrification (~1000 times smaller) when compared to the rates of the other processes and also to the insensitivity of the measured responses to changes in the denitrification parameter.The rates or rate constants for the four processes compared favorably with those reported by others. Highest nitrification rates were found in agricultural soils [1–5 and 1–34 mg N kg−1 day−1) compared with a forest soil (< 1 mg N kg−1 day−1). Rates of mineralization (0.6–1.5 mg N kg−1 day−1) and immobilization (0.1–4 mg N kg−1day−1) were similar in all soils, although immobilization was favored in the agricultural sandy loam. Denitrification was considerably higher in the agricultural clay loam (> 500 μg N kg−1day−1) than in the coarser textured soils (~10 μg N kg−1day−1).Some experimental data could not be fit with zero- or first-order kinetics, however this was most likely because the model did not account for all of the processes occurring in these soils, rather than limitations to the parameter estimation procedure itself. Even with the relatively high degree of experimental variability inherent in measuring N pool sizes and 15N ratios, reasonably good parameter estimates were obtained in these laboratory incubations, demonstrating the feasibility of simultaneously estimating the rates of several N cycle processes. The trends in N cycle rates among the soils investigated were consistent with those normally associated with forest and agricultural soils, further corroborating the utility of this method.

Nitrogen transformation in coastal sands and dune soils

Nitrification, N-leaching and NO 3 − -N reduction were studied in coastal sands and dune soils. Surprisingly high rates of nitrification were found when immature dune sands (that is uncolonized sands; and those from below Ammophila and H. rhamnoides ) were incubated at 25 °C with (NH 4 ) 2 SO 4 ; with rates of NO 3 − -N production eventually reaching those found in mature dune and garden soils. Unlike soils, the process occurred in sands only after an initial 7 day lag following substrate addition, presumably the time required for a substantial population of nitrifiers to develop. High concentrations of NO 2 − -N accumulated in immature dune sand, but not soil samples, a feature related to the alkalinity (pH 8·5) of the sands. Nitrate reduction was rapid in immature sands, and dune and garden soils, with NO 2 − -N accumulating in immature sands, but not soils. Both added NO 2 − -N and NO 3 − -N were readily leached by water from sand and dune soil, while NH 4 + -N was relatively fixed. The relevance of these results to N-fertilization of coastal sand dunes is commented upon.

Influence of Liming Rate on Holly, Azalea, and Juniper Growth in Pine Bark

Abstract Rooted cuttings of Ilex crenata Thunb. ‘Helleri’, Rhododendron obtusum Planch. ‘Rosebud’, and Juniperus chinensis L. ‘San Jose’ were grown in a 100% pine-bark medium amended with dolomitic limestone at 0 to 8 kg m-3 with resulting pH from 3.4 to 7.2. Except for juniper at 2 kg m-3, growth was not increased by liming, and 8 kg m-3 tended to reduce shoot and root growth. This reduced growth was attributed in part to greater NH4 adsorption by the bark, reducing the amount available for plant uptake, and a higher nitrification rate, leading to an elevated NO3 to NH4 ratio in the medium. Liming pine bark to improve growth of these woody plants may be unnecessary.

Overturn in a hypertrophic, warm, monomictic impoundment (Hartbeespoort Dam, South Africa)

A major decrease in air temperature with an increase in wind stress created thermal instability resulting in overturn. Surface oxygen values decreased from 12.6 (170% saturation) prior to overturn to 0.4 mg · l−1 (5.7%) after overturn. Recovery of surface oxygen concentrations to supersaturation took approximately three months. Changes in the nitrogen balance after overturn indicated that extremely high rates of nitrification occurred. Little change in phosphorus concentration was observed. Surface chlorophyll concentrations decreased from 235 to approximately 2 mg · m−3, resulting in very low primary production values (Amax = 12.4 mg C m−3 h−1). Reduced rates of primary production were maintained for several months after overturn, mainly owing to the low ratio of Zeu/Zm (0.17). No significant changes occurred in the total bacterial population other than a redistribution within the water column. Significant changes occurred in the distribution and density of the zooplankton population. No fish kills were observed although fish populations were oxygen-stressed.

THE DESIGN OF A NEW HIGH RATE NITRIFICATION FILTER FOR AQUACULTURE WATER REUSE

AbstractA new design in a high rate nitrification system has been tested at the laboratory scale. Ammonia removal rates per unit of filter volume at influent ammonia levels of 0.02 mg NH3‐N were observed to be 5 to 10 times more rapid than rates observed in conventional field‐scale nitrification filters. At these levels 95 to 99% ammonia removal has been achieved with filter detention times as short as 3 minutes. The data are compared to data for various field units and the reasons for the observed high removal rates are discussed. The possibility of retaining these high efficiencies in scaled‐up filters is also discussed.

Nitrification in relation to growth in Aspergillus flaws

Relatively high nitrification rates were attained with Aspergillus flavus grown aerobically with high concentrations of glucose and peptone. l-Aspartate added after depletion of glucose gave only a moderate increase in the total nitrate yield, but a marked specific response was observed when l-aspartate was added as nitrate production started to level off. The effect of glucose, glucosamine and N-acetylglucosamine on actively nitrifying cultures was studied. The first two had an inhibitory effect due to nitrate assimilation, while N-acetylglucosamine had virtually no effect. Young mycelium had a cytochrome type of terminal oxidase which was observed to shift to a flavoprotein type as the mycelium became fully grown.