Disappearance Of Nitrate Research Articles

Modeling of nitrate disappearance and sludge rising in a settling column system

The determination of different rates of endogenous nitrate respiration due to biomass stratification throughout the depth of a sludge blanket is essential to assess the factors affecting the sludge rising in secondary clarifiers. In this study, an extension of the solids flux theory in conjunction with nitrate mass balance was used to model the fate of nitrate in a sludge settling column. The model-predicted nitrate concentrations agree well with those experimentally determined. A new term, sludge stability index, was introduced to reflect the sludge rising time and the corresponding critical nitrate concentration necessary for causing sludge rising. The model predicted well the observed sludge rising times occurring under batch settling column experiments with initial biomass and nitrate concentration ranging from 2000 to 5000 mg l −1 and 10 to 30 mg-N l −1, respectively. Furthermore, simulation results indicated that both the sludge rising time and CNC are significantly affected by k ENR.

Cellular regulation of nitrate uptake in denitrifying Flexibacter canadensis

Nitrate uptake and its regulation were investigated using an ion-specific nitrate electrode for denitrifying Flexibacter canadensis under anaerobic conditions. Glucose supported a greater rate of nitrate uptake than did glycerol, glutamate, lactose, cellobiose, or ethanol. Nitrate uptake closely approximated Michaelis--Menten kinetics; the estimated Ks(glucose) and apparent Km(nitrate) for nitrate uptake were 21 and 44 microM, respectively. Nitrate disappearance was correlated with nitrite accumulation, and nitrate had an inhibitory effect on nitrite reduction. Oxygen inhibition of nitrate uptake increased as the percent air saturation increased, and reversed readily as the percent air saturation decreased. The minimal air saturation showing inhibition of nitrate uptake was about 2-4%. Azide and cyanide completely inhibited nitrate uptake. No nitrate uptake was observed in cells grown in the presence of 1 or 5 mM tungstate (no added molybdate). When molybdate (100-200 microM) was present in the medium, nitrate uptake was exhibited by organisms grown with 1 mM, but not with 5 mM, tungstate, indicating that nitrate uptake was dependent on the presence of an active nitrate reductase, and that competition between tungsten and molybdenum occurred during the formation of nitrate reductase. Nitrite production from nitrate by whole cells but not cell-free extracts was inhibited by 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone, indicating that nitrate and (or) nitrite transport depended upon the electrochemical proton gradient.

Nitrate Disappearance in an lrrigation Pond

Nitrate Disappearance in an lrrigation Pond

Real-Time Control of Wastewater Treatment Systems Using ORP

Oxidation-Reduction Potential (ORP) can be used as a process control parameter for real-time automated control of batch sewage treatment systems. Results suggest that ORP has great potential for the control of anoxic sequences, since the distinct breakpoint in the ORP-time curve correlates to the disappearance of nitrates.

Nitrate reduction in seedlings of carob (Ceratonia siliqua L.)

summaryThe distribution of nitrate reduction in young carob plants (Ceratonia siliquaL. cv. Mulata) was studied. Plants (three months old) were grown in aerated nutrient solutions under greenhouse conditions. Reduction of nitrate was estimated both in the leaves and in the roots by: (a) accumulation of nitritein vitro, (b) accumulation of nitritein vivoand (c) disappearance of nitratein vivo.Disappearance of nitratein vivooffered the closest estimation of the rate of nitrate reduction.Leaves consistently showed rates of nitrate reduction lower than those in roots, regardless of assay method. Lowering root temperature had no marked effect on the distribution of nitrate reductase activity in the plant; increasing nitrate concentration in the shoot, however, markedly increased leaf nitrate reduction. The relatively low level of nitrate reductase in leaves appears to be caused mainly by a limitation of nitrate transport from root to shoot. Nitrate reduction takes place in both the root and the shoot of young carob plants with the shoot accounting for approximately 20% of total nitrate reduction in the plant.

Metabolism of pyridine and 3-hydroxypyridine under aerobic, denitrifying and sulfate-reducing conditions

The transformation of pyridine and several hydroxypyridines was investigated under different physiological conditions. Pyridine and 2-, 3- and 4-hydroxypyridine were metabolized aerobically within 9 days in a mineral salt medium inoculated with 10% sewage sludge. Under anaerobic conditions in the presence of nitrate or sulfate, pyridine and 3-hydroxypyridine were metabolized after a lag period of 2 months, while no transformation of 2- or 4-hydroxypyridine was detected. Experiments with14C-labeled-pyridine showed that under denitrifying as well as under sulfate-reducing conditions pyridine was oxidized to carbon dioxide. Disappearance of nitrate and sulfate under anaerobic conditions was 79% and 85%, respectively, of the amount predicted from the stoichiometric equation for the complete transformation of pyridine.

Reduction of Nitrate in Aquifer Microcosms by Carbon Additions

AbstractAquifer microcosms were used to examine the effects of NO−3 and C amendments on groundwater from the Claiborne aquifer. Nitrate concentrations of 12.17 mg L−1 in aquifer microcosms were reduced 0.92%/d to 5.84 mg L−1 by the addition of 10 mg C L−1 for 35 d. Nitrate disappearance correlated with increases in number of denitrifiers and dissolved N2O concentration and decreases in dissolved oxygen, suggesting biological denitrification. Nitrate/chloride ratios decreased in microcosms with 10 mg C L−1 added and then increased when the C addition was removed. Carbon additions of 0.4 mg C L−1 had no effect on the microbial or chemical properties of the microcosms. Nitrous oxide levels in wells sampling the Claiborne aquifer showed an increase with depth, indicating N2O production within the aquifer. Microcosms are useful tools to examine biological transformations of chemical contaminants in unconsolidated aquifer material. The remediation of NO−3 contaminated aquifers by organic infusion is possible and appears to be a function of microbial denitrification.

Direct measurements of nanomolar nitrate uptake by the marine diatom Phaeodactylum tricornutum (Bohlin). Implications for studies of oligotrophic ecosystems

A new automated procedure for nanomolar nitrate analysis was applied to the study of uptake of low nitrate concentrations (< 100 ngat l−1) by phytoplankton. The precision of this analytical method (± 3 ngat l−1) made it possible to monitor the absorption of very low quantities of nitrate over short term periods by a low cell-density culture of the marine diatom Phaeodactylum tricornutum, where the levels of particulate nitrogen and chlorophyll were equivalent to those found in oligotrophic areas (0.5 µgat N l−1 and 0.4 µg l−1 respectively). By continuous monitoring of nitrate disappearance from the culture medium, we are able to describe accurately the transient uptake responses of the diatom after a spike addition of trace quantities of nitrate and thus to provide new information on the still largely unknown small-scale phenomenon of pulsed nitrate supply in the upper layer of stratified oceans and rapid uptake of these nitrate patches by phytoplankton. The results show that a N-limited culture of Phaeodactylum tricornutum is immediately capable of taking up trace quantities of nitrate (< 100 ngat l−1) at high rates (0.10–0.14 h−1) . These initial rates are one order of magnitude higher than the theoretical rates calculated from the Michaelis-Menten equation and are close to the level of V max (0.15 h−1) obtained when cells are exposed to saturating nitrate concentrations. This rapid initial uptake would be a considerable advantage in oligotrophic areas where nanomolar nitrate supply is thought to be episodic. The present results suggest that phytoplankton evolve adaptations to utilize the available nitrate at the spatial and temporal scales at which it occurs. On the other hand, we can consider this physiological adaptation as evidence of nitrate pulses in the field which would invalidate the steady-state approach to the oligotrophic ecosystems.

On the discrepancies between a colorimetric and isotopic method for measuring nitrate utilization in nutrient-depleted waters: implications for the design of experimental protocols in new production studies

Colorimetric analyses of nitrate disappearance from seawater have been compared with isotopic analyses of 15N-labelled nitrate incorporation into particulate matter. The slope (1.41) of a regression line calculated from 19 sample pairs gathered during 6 time-series experiments and 2 single end-point incubations showed that nitrate incorporation is positively related to changes in nitrate concentration but that it accounts only for 71% of nitrate disappearance. 15N-isotope dilution as a consequence of nitrification, if any, would not fully explain discrepancies between the two analytical procedures. A further possible mechanism responsible for the imbalance between nitrate-incorporation and -disappearance rates suggests losses of 15N label from plankton biomass to an unanalyzed pool (dissolved organic nitrogen?) which increase (up to 65%) with incubation time. The lack of 15N-mass balance calls for the need to consider additional nitrogen pools in 15N budgets of isotope experiments and not only substrate and biomass pools as has been done so far.

Observations of phytoplankton and nutrients from a Lagrangian drifter off northern California

A Lagrangian drifter was deployed in a cold filament off northern California as part of the Coastal Transition Zone program. The drifter was equipped with an optical package (consisting of a spectroradiometer, a fluorometer, and a beam transmissometer) suspended at 8.5‐m depth and a water sampler suspended at 16.3‐m depth. The drifter was recovered after 8 days. Optical, chemical, and biological properties changed considerably as the drifter moved offshore in the cold filament. Concentrations of phytoplankton chlorophyll increased rapidly in the first 2 days, in parallel with the disappearance of nitrate and nitrite. After this initial period, chlorophyll decreased gradually over the next 6 days with prominent diurnal fluctuations present in the last 3 days. Water transparency also showed similar long‐term as well as diurnal fluctuations. The phytoplankton community became increasingly dominated by large centric diatoms throughout the deployment. Although total cell volume was higher towards the middle of the deployment, this increase occurred without a parallel increase in chlorophyll. In addition, total particulate concentrations were highest nearshore. Although the drifter slippage was approximately 1 cm/s, the biological, chemical, and physical characteristics of the water were affected by both in situ changes and vertical motions of the water. These results are generally consistent with results from other up welling studies.

Biodegradation of 2-furaldehyde under nitrate-reducing and methanogenic conditions

Nitrate-reducing and methanogenic microbial consortia capable of using 2-furaldehyde (furfural) as a sole source of carbon and energy were isolated from a mixture of soil and municipal sewage and from municipal anaerobic digestor sludge, respectively. Under nitrate-reducing conditions, more than 97% of the furfural was biodegraded in 0.25, 1.5, 4 and 32 d at initial substrate concentrations of 0.5, 5, 50 and 500 ppm, respectively. In all cases microbial populations were able to reduce furfural levels to less than the detection limit of 20 ppb as measured by HPLC. At 500 ppm, there was a 12-d lag period before detectable activity was noted, while there was no lag period at the lower concentrations tested. When the disappearance of both furfural (50 ppm) and nitrate was measured, the molar ratio of nitrate to furfural consumed was approximately 4.2:1, Which is in good agreement with the theoretical ratio of 4.0:1. The biodegradation of furfural was generally more rapid under methanogenic than under nitrate-reducing conditions. The methanogenic consortium was able to metabolize 97% of the furfural in 2, 4, 48 and 144 h at initial concentrations of 0.5, 5, 50 and 500 ppm, respectively. No lag period was noted at any concentrations tested. As under nitrate-reducing conditions, populations were able to reduce furfural levels to less than 20 ppb. Complete metabolism of furfural in cultures that received an initial concentration of 50 ppm resulted in the production of 0.056 mM methane or 43% of the theoretical yield that would result from complete conversion of the material to carbon dioxide and methane. This is the first report of the biodegradation of furfural under nitrate-reducing conditions.

In vitro and in situ studies on nitrate disappearance in water-sediment systems of the Camargue (southern France)

Results of in vitro and in situ experiments on nitrate disappearance from water-sediment systems in the Camargue are described. In the in vitro experiments two factors were studied: temperature and organic matter. After a first addition of KNO3 to these sediments, the concentration of organic matter exerted a strong influence on the disappearance rate of nitrate at 25 °C and 15 °C but not at 2 °C. After a second addition of nitrate at 25 °C and 15 °C the denitrification rate increased by approximately 10%, probably because the activity of the bacterial population had increased. Experiments in situ in freshwater temporary marshes showed that nitrate disappeared at approximately twice the rate at similar temperature in vitro. After the first addition of nitrate in the in vitro experiments the concentration of nitrite in the water above the sediment reached about 10% of the concentration of total dissolved inorganic nitrogen at 2 °C and 15 °C. These high concentrations were not found after the first addition at 25 °C or after the second addition of nitrate at 25 °C and 15 °C. In the in situ experiments, however, high concentrations of nitrite were found.

Denitrification losses from puddled rice soils in the tropics

Although denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice (Oryza sativa L.) soils, direct field measurements of denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of denitrification in rice fields. The direct recovery of (N2+N2O)-15N from 15N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N2+N2O)-15N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the 15N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N2+N2O)-15N from added nitrate. In the absence of runoff and leaching losses, the amount of (N2+N2O)-15N evolved from 15N-labeled nitrate was consistently less than the unrecovered 15N in 15N balances with labeled nitrate, which presumably represented total denitrification losses. This finding indicates that the measured recoveries of (N2+N2O)-15N had underestimated the denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N2+N2O)-15N failed to confirm the appreciable denitrification losses often estimated by the indirect difference method. This method, which determines denitrification losses by the difference between total 15N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and 15N-balance studies suggest that nitrification-denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of denitrification losses when soils are flooded and puddled for production of rice.

Short-term regulation of nitrate uptake by a ‘pump and leak’ mechanism in the acidophilic nonvacuolated alga, Cyanidium caldarium

In the nonvacuolated acidophilic thermophilic red alga, Cyanidium caldarium , nitrate uptake and reduction can be separated by measuring disappearance of nitrate from the suspension medium using, in in vivo experiments, cyanate, a competitive inhibitor of algal nitrate reductase. Cyanate selectively inhibited nitrate reduction at concentrations that did not significantly affect nitrate uptake, photosynthesis or respiration. Its use proved that short-term control of intracellular nitrate through the increase of a carrier-mediated nitrate efflux took place when nitrate reduction was inhibited. The occurrence of the high- and low-affinity nitrate uptake systems in cells grown in nitrogen-limited conditions, as previously reported, suggests a ‘pump and leak’ mechanism operating at the plasmalemma level to regulate nitrate uptake and intracellular nitrate: the high-affinity nitrate transport system mediated by proton cotransport (irreversible) operates the influx, while the low-affinity transport (reversible) operates influx or efflux according to cell requirements. Kinetic analysis of cyanate inhibition in cells taken from low-nitrate medium supports this hypothesis and reveals that, in Cyanidium , intracellular nitrate is probably compartmented in the cytosol.

The nitrogen cycle in shallow water sediment systems of rice fields. Part 1: The denitrification process

Denitrification causes important losses of N-fertilizer in rice-fields, where high temperature and high production of organic matter favour denitrification losses. Two techniques have been used to quantify the denitrification losses: the 15N technique, which can be used to quantify the amount finally incorporated, and the acetylyne inhibition technique which is a direct measure of the quantities lost. Both techniques were applied in enclosures (diameter = 44 cm) in the field while moreover bio-assays in 3 l glass beakers were carried out. In all experiments where nitrate was added we found a rapid decrease of nitrate; usually about 30–50% of the nitrate that disappeared was recovered as N2O. As in one experiment, in which we measured the N2O disappearance rate as well, the N2O itself decreased at a rather constant rate of 20% per day, a correction must be made for this N2O decrease in the calculations of the nitrate disappearance rate. Although we have only one series in which the decrease of N2O was measured, the mathematical analysis indicates that as much as 80% of the N-fertilizer is actually lost. This figure is in full agreement with the 15N experiments; if the 15N was applied early only about 7% was recovered in soil and plants, while if it was applied later (after 7 weeks) about 20% was incorporated. Denitrification rate could be fitted on an negative exponential regression line; the rate constant increased during the summer. It is suggested that organic matter caused this increase. During denitrification considerable quantities of nitrite appear, which later on disappear again by processes still unknown; the nature of the available organic matter may be important for this nitrite production. With N-serve we tried to inhibit NH3 oxidation. In this way we tried to prevent the considerable N losses and to demonstrate that the nitrite produced in our experiments was not derived from NH3 oxidation. N-serve, however, had very little influence. It is probably inactivated by absorption onto the sediments. From these results it is suggested that the efficiency of N-application may be considerably increased by using low doses of N-fertilizer, but applied late in the growing season, e.g. 7 weeks after sowing. This favours environmental protection as well.

Nitrogen Utilization in Lemna

(13)N-labeled nitrate was used to trace short-term nitrate influx into Lemna gibba L. G3 in experiments where disappearance of both radioactivity and total nitrate from the incubation medium was measured continuously and simultaneously. In plants performing net nitrate uptake from an initial nitrate concentration of 40 to 60 micromolar, there was no discrepancy between net uptake and influx, irrespective of the N status of the plants, indicating that concomitant nitrate efflux was low or nil. Plants treated with tungstate to inactivate nitrate reductase were able to take up nitrate following induction of the uptake system by exposure to a low amount of nitrate. Also, in this case, net uptake was equivalent to influx. In tungstate-treated plants preloaded with nitrate, both net uptake and influx were nil. In contrast to these observations, a clear discrepancy between net uptake and influx was observed when the plants were incubated at an initial nitrate concentration of approximately 5 micromolar, where net uptake is low and eventually ceases. It is concluded that plasmalemma nitrate transport is essentially unidirectional in plants performing net uptake at a concentration of 40 to 60 micromolar, and that transport is nil when internal nitrate sinks (vacuole, metabolism) are eliminated. The efflux component becomes increasingly important when the external concentration approaches the threshold value for net nitrate uptake (the nitrate compensation point) where considerable exchange between internal and external nitrate occurs.

Ammonium thresholds for simultaneous uptake of ammonium and nitrate by oyster-pond algae

Natural microalgal populations and axenic algal isolates from oyster ponds have been grown either in situ or in controlled conditions, in the presence of ammonium and nitrate as nitrogen sources. Both ions were added at various concentrations, up to 50 μg-at. N·l −1; other nutrients were in excess. In one experiment, urea was also added. Uptake of nitrate was followed by measuring disappearance of nitrate from the medium, and by incorporation of 15NO 3; nitrate reductase (NR) activity and the intracellular nitrate pool were also measured. The uptake of nitrate was prevented by the presence of ammonium above a concentration which varied according to species. The ammonium threshold (in units of μg-at. N·l −1) was ≈ 30 for natural populations and the diatom Navicula ostrearia Bory, ≈ 21 for Nitzschia ovalis (sensu Hustedt), and ≈ 44 for Amphora coffeaeformis (sensu Hendey). Nitrate uptake started at a rate which was ≈ 39% of the eventual maximum rate observed for the natural populations, and from 11 to 17% for cultured strains. The initial low rate was maintained until the ambient ammonium concentration had decreased to ≈ 7.5 μg-at. N·l −1, except for A. coffeaeformis which shifted from slow to fast nitrate uptake at 23.5μg-at. N·l −1. The nitrate uptake system then operated at a slightly higher rate than the one for ammonium (ammonium uptake/nitrate uptake = 0.86). Cultures with an initial ammonium concentration lower than the threshold values did not show an initial low rate or a lag phase for uptake of nitrate. NR activity was detectable even in the presence of ≈ 30 μg-at. NH 4-N·l −1 in the external medium. When urea and nitrate were presented simultaneously, urea was not taken up preferentially, as reported elsewhere; uptake was initially at a reduced rate until the external nitrate concentration decreased to 3.7 μg-at. N·l −1. Then the rate of urea uptake increased to a maximum. It is suggested that because oyster-pond algae have evolved in an environment where concentrations of ammonium, nitrate, and organic nitrogen are continuously high, the threshold of inhibition by ammonium of uptake of these compounds is much higher than for similar pelagic and neritic species, so that they are able to assimilate other sources of nitrogen, such as nitrate and urea, simultaneously with ammonium.

Denitrification studies in a temperate forest catena soil

Formation of ammonium during the reduction of nitrate under moderate and strict anaerobic incubation of two topsoils of a temperate forest catena, an acid mull and an anmoor was studied. In mull, both conditions of incubation caused reduction of nitrate and release of ammonium. The accumulation of ammonium continued even when there was no nitrate left hence indicating the formation of ammonium apparently through desamination of organic matter. Whereas, in anmoor neither any such formation of ammonium nor any significant reduction of nitrate was observed in the case of moderate anaerobic incubation. But under strict anaerobic incubation, progressive disappearance of nitrate was encountered from the beginning up to 30 days and this was accompanied by an increasing accumulation of ammonium in this soil. Yet this accumulation stopped when there was no nitrate left. Thus, the formation of ammonium is caused by the reduction of nitrate in anmoor.

The activities of two pathways of nitrate reduction in Rhodopseudomonas capsulata

(1) The disappearance of nitrate from suspensions of intact, washed cells of Rhodopseudomonas capsulata strain N22DNAR+ was measured with an ion selective electrode. In samples taken from phototrophic cultures grown to late exponential phase, nitrate disappearance was partially inhibited by light but was not affected by the presence of ammonium. Nitrate disappearance from samples from low density cultures in the early exponential phase of growth was first inhibited and later stimulated by light. In these cells ammonium ions inhibited the light-dependent but not the dark disappearance of nitrate. It is concluded that cells in the early exponential phase of growth possess both an ammonium-sensitive, assimilatory pathway for nitrate reduction (NRI) and an ammonium-insensitive pathway for nitrate reduction (NRII) which is linked to respiratory electron flow and energy conservation. In cells harvested in late exponential phase only the respiratory pathway for pitrate reduction is detectable. (2) Nitrate reduction, as judged by the oxidation of reduced methyl viologen by anaerobic cell suspensions, was measured at high rates in those strains of R. capsulata (AD2, BK5, N22DNAR+) which are believed to possess NRII activity but not in those strains (Kbl, R3, N22) which only manifest the ammonium-sensitive NRI pathway. On this basis we have used nitrate-dependent oxidation of reduced methyl viologen as a diagnostic test for the nitrate reductase of NRII in cells harvested from cultures of R. capsulata strain AD2. The activity was readily detectable in cells from cultures grown aerobically in the dark with ammonium nitrate as source of nitrogen. When the oxygen supply to the culture was withdrawn, the level of methyl viologen-dependent nitrate reductase increased considerably and nitrite accumulated in the culture medium. Upon reconnecting the oxygen supply, methyl viologen-dependent nitrate reductase activity decreased and the reduction of nitrate to nitrite in the culture was inhibited. It is concluded that the respiratory nitrate reductase activity is regulated by the availability of electron transport pathways that are linked to the generation of a proton electrochemical gradient.

Endogenous nitrate loss as an assay for nitrate reduction in vivo

An in vivo assay method for nitrate reduction is proposed, based on the use of endogenous nitrate rather than on the accumulation of nitrite. Loss of endogenous nitrate and accumulation of nitrite were studied in barley (Hordeum vulgare L. cv. Gars Clipper ex Napier) leaves. Leaf sections were incubated in the dark in a gaseous environment of air or N2. Nitrate disappeared under both conditions, the highest loss being observed in tissue under anaerobiosis. Nitrite accumulated only in leaf sections under anaerobiosis, but the amount of nitrite accumulated was much lower than the amount of nitrate lost. A comparative study of the capacity of barley leaf sections to use endogenous nitrate and accumulate nitrite showed that both activities were dependent on temperature in a manner characteristic of enzymatic reactions. Disappearance of endogenous nitrate increased with increasing levels of nitrate in the tissue.