Chemical decomposition and fixation of nitrite in acidic pasture soils and implications for measurement of nitrification

The fate of added ¹⁵N-labelled nitrite (¹⁵NO₂^?-N) was investigated in a laboratory experiment with two acidic pasture soils collected from northeast Victoria (Maindample and Ruffy) and an alkaline soil collected from Waurn Ponds, Victoria, Australia. Two and a half hours after mixing and extraction, the ¹⁵NO₂^?-N recovered in 2 M KCl extracts was 22% and 33% of the applied NO₂^? in Maindample and Ruffy soils, respectively, and 100% in the Waurn Ponds soil. There was no difference in NO₃^? recovered with and without NaClO₃ addition during this procedure, suggesting that biological oxidation of the applied NO₂^? was not the cause of the low recovery. Of the applied ¹⁵NO₂^?-N, 21% and 20% in the acidic Maindample and Ruffy soils, respectively, were recovered from the organic pool where it is believed to have been chemically fixed, leaving the total loss of ¹⁵NO₂^? as 57% and 47% from these two soils, most likely due to chemical self-decomposition to NO and NO₂. When extracted with 0.005 M KCl, the salt concentration used in the short-term nitrification assay (SNA) 51% and 42% of applied ¹⁵NO₂^? were recovered in the extract from Maindample and Ruffy soils, respectively, but the total losses were only 9% and 10% of the applied ¹⁵NO₂^?-N, respectively. The chemical fixation and self-decomposition of NO₂^? in acidic soils are likely to cause an underestimate of nitrification rates by SNA.     

Trends and Spatiotemporal Patterns of Tropospheric NO<Subscript>2</Subscript> over China During 2005–2014

Nitrogen dioxide (NO₂) is one of the major atmospheric pollutants, and the concentration of NO₂ is regarded as one of the indicators of air quality. In the past decades, China has experienced rapid economic growth and severe NO₂ pollution to match. We evaluate the trends and spatiotemporal patterns of tropospheric NO₂ over mainland China from 2005 to 2014 using vertical column density (VCD) datasets retrieved from the Ozone Monitoring Instrument (OMI). Results show that from 2005 to 2014, NO₂ pollution regions have enlarged at the national scale, and high NO₂ VCDs are mainly concentrated over highly populated regions in eastern China. The year 2011 is the turning point. Tropospheric NO₂ VCDs first significantly increase by 0.19?×?10¹⁵ molec cm^?2?year^?1 (R ²?=?0.94, P?=?0.002) from 2005 to 2011, and then decrease by 0.21?×?10¹⁵ molec cm^?2?year^?1 (R ²?=?0.97, P?=?0.016) from 2011 to 2014. Since 2011, tropospheric NO₂ VCDs over central-east China decrease remarkably. Tropospheric NO₂ VCDs is higher in November (3.630?×?10¹⁵ molec/cm²), December (4.758?×?10¹⁵ molec/cm²), and January (4.863?×?10¹⁵ molec/cm²), while lower in July (1.684?×?10¹⁵ molec/cm²), August (1.627?×?10¹⁵ molec/cm²), and September (1.703?×?10¹⁵ molec/cm²), indicating that winter and spring are the most polluted seasons. Due to the huge gap in population density and industry development between western and eastern China, the spatial pattern of tropospheric NO₂ VCDs shows large west-east difference.     

Simultaneous Absorption of SO2 and NO in a Stirred Tank Reactor with NACLO2/NAOH Solutions

The wet scrubbing combined SO_x/NO removal system is one ofthe advanced air pollution control devices. This study tries tounderstand the kinetics of the absorption in the system. The absorption of SO₂ and simultaneous absorption of SO₂ and NO, whose concentrations are typical for flue gases emittedfrom coal-fired power plants, in a stirred tank reactor with NaClO₂/NaOH solutions were carried out at 50 °C.The liquid-side and gas-side mass transfer coefficients of the system were determined. The results indicate that the absorptionof SO₂ is completely gas-film controlled if the NaOH concentration is greater than 0.1 M or the NaClO₂ concentration is greater than 0.2 M. Adding SO₂ would decrease the absorption rate of NO; however, the addition of NO has no effect on the absorption rate of SO₂. The existence of O₂ has no significant effect on the absorption rate of SO₂ and NO in the combined SO_x/NO removal tests.     

Biological oxidation of nitric oxide in a humisol

Consumption of nitric oxide (NO) in a humisol was studied at 0.1–2 ppmv NO, a range representative of NO concentrations in ammonium-fertilized soil. Denitrification was not a major sink for NO. The principal NO-consuming reaction was a biological oxidation, leading ultimately to nitrate (NO₃ ^–). Nitrogen dioxide (NO₂) and nitrite (NO₂ ^–) may have been intermediates in this pathway. An abiological reaction accounted for about 25% of the NO-consuming activity in soil at 90% H₂O (d.w.) and 25^oC, but contributed relatively more to total NO consumption at higher temperatures. Biological NO-consuming activity was highest at 25^oC, while the abiological activity increased exponentially with temperature. The product of the abiological reaction was neither NO₃ ^–, NO₂ ^–, nor nitrous oxide (N₂O), and the reaction did not require O₂. Received: 12 March 1996     

Influence of pH on the release of NO and N2O from fertilized and unfertilized soil

Summary NO and N₂O release rates were measured in an acidic forest soil (pH 4.0) and a slightly alkaline agricultural soil (pH 7.8) after the pH was adjusted to values ranging from pH 4.0 to 7.8. The total release of NO and N₂O during 20 h of incubation was determined together with the net changes in the concentrations of NH ₄ ⁺ , NO ₂ ^– and NO ₃ ^– in the soil. The release of NO and N₂O increased after fertilization with NH ₄ ⁺ and/or NO ₃ ^– ; it strongly decreased with increasing pH in the acidic forest soil; and it increased when the pH of the alkaline agricultural soil was decreased to pH 6.5. However, there was no simple correlation between NO and N₂O release or between these compounds and activities such as the NO ₂ ^– accumulation, NO ₃ ^– reduction, or NH ₄ ⁺ oxidation. We suggest that soil pH exerts complex controls, e.g., on microbial populations or enzyme activities involved in nitrification and denitrification.     

Influence of ambient acidity on the absorption of NO3 − and NH4 + by tomato punts

Abstract

The effects of ambient acidity on NO₃ ^? and Nh₄ ⁺ absorption by 26‐day‐old tomato plants (Lycopersicon esculentum Mill.) were examined in solution culture. The absorption rate per unit root mass was measured for 6 hr. The NO₃ ^? absorption rate from 0.4 mM NaNO, was 36% greater at pH 4.5 than at pH 6.5. In contrast, the NhY absorption rate was approximately 42% greater at pH 5.5 or 6.5 than at pH 4.5. The presence of equimolar NHr from 0.4 mM NH^NO, decreased the NO, absorption rate at pH 5.5 or 6.5 but did not reduce the rate at pH 4.5. The NO, absorption rate was inhibited less at pH 5.5 when equimolar NHr was supplied from 0.2 mM (NH₄)₂S0₄ as opposed to NH₄NO₃. At pH 5.5, the N0₃ ^? absorption rate increased with increased #OPNH₄#CP₂SO₄ concentration. The presence of equimolar NO₃ ^? supplied as either NaNO₃ or NH₄NO₃ had no effect on the NH₄ ⁺ absorption rate at pH 5.5 or 6.5. However, at pH 4.5, the NH₄ ⁺ absorption rate was slightly reduced from NH₄NO₃ solutions relative to that from a (NH₄)₂S0₄ solution.     

Contrasting response of two forest soils to nitrogen input: rapidly altered NO and N2O emissions and nirK abundance

Denitrification represents one of the main microbial processes producing the primary and secondary greenhouse gases nitrous oxide (N₂O) and nitric oxide (NO) in soils. It is well established that abiotic factors like the soil water content and the availability of nitrogen (N) are key parameters determining the activity of denitrifiers in soils. However, soils differing regarding their characteristics such as the content of C_org, the soil texture or the pH value may respond in specific manners to equivalent changes in soil moisture and N input. Thus, short-term incubation experiments were performed to test and compare the capacity of two contrasting Austrian forest soils to respond to mineral N application at increased soil water contents. Soils from the pristine Rothwald forest (rich in C_org) and the more acidic Schottenwald forest (poor in C_org) were amended with either NH ₄ ⁺ -N or NO ₃ ^? -N and were incubated at 40% and 70% water-filled pore space for 4 days. Changes in mineral N pools, nitrite reductase activity and NO and N₂O emission rates were measured, and the abundance and structural community composition of the functional group involved in nitrite reduction were analysed via quantitative real-time polymerase chain reaction and terminal restriction fragment length polymorphism analysis of the nirK gene. Rapid and distinct activity responses to increased soil moisture and altered mineral nitrogen availability were observed in two contrasting forest soils. In both soils, nitrogen oxide emission rates were stimulated by N inputs and, depending on the soil moisture status, either NO or N₂O emission was prevailing. However, different N cycling processes appeared to predominate in either soil under equivalent treatment. Nitrogen oxide emissions peaked following NO ₃ ^? application in Schottenwald soils but were the highest after NH ₄ ⁺ application in Rothwald soils. Denitrifying (nirK) communities differed significantly in Rothwald and Schottenwald soils; however, changes in the community structure were marginal during the short-term incubation. Abundances of nirK genes remained unaffected by N application in either soil. The soil water content affected nirK gene abundances only in Rothwald soil, indicating a distinct reaction of nitrite reducing communities in the two soils.     

N2O and NO production in various Chinese agricultural soils by nitrification

Eleven types of agricultural soils were collected from Chinese uplands and paddy fields to compare their N₂O and NO production by nitrification under identical laboratory conditions. Before starting the assays, all air-dried soils were preincubated for 4 weeks at 25 °C and 40% WFPS (water-filled pore space). The nitrification activities of soils were determined by adding (NH₄)₂SO₄ (200 mg N kg⁻¹ soil) and incubating for 3 weeks at 25 °C and 60% WFPS. The net nitrification rates obtained fitted one of two types of models, depending on the soil pH: a zero-order reaction model for acidic soils and one neutral soil (Group 0); or a first-order reaction model for one neutral soil and alkaline soils (Group 1). The results suggest that pH is the most important factor in determining the kinetics of soil nitrification from ammonium. In the Group 1 soils, initial emissions (i.e. during the first week) of N₂O and NO were 82.6 and 83.6%, respectively, of the total emissions during 3 weeks of incubation; in the Group 0 soils, initial emissions of N₂O and NO were 54.7 and 59.9%, respectively, of the total emissions. The net nitrification rate in the first week and second-third weeks were highly correlated with the initial and subsequent emissions (i.e. during the second and third weeks), respectively, of N₂O and NO. The average percentages of emitted (N₂O+NO)-N relative to net nitrification N in initial and subsequent periods were 2.76 and 0.59 for Group 0, and 1.47 and 0.44 for the Group 1, respectively. The initial and subsequent emission ratios of NO/N₂O from Group 0 (acidic) soils were 3.77 and 2.52 times, respectively, higher than those from Group 1 soils (P<0.05).     

Effects of acidity of the water culture solution on uptake of nutrients by the root of Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa)

The condition around coniferous trees in the soil is becoming gradually acidic when acid rain falls continuously. Nutrient uptake by the roots of coniferous trees could be affected in such environmental change of root zone. The experiments of water culture of coniferous seedlings in modified systems were carried out using (2-and, 3-year-old) of Japanese cedar(Cryptomeria japonica) and, Japanese cypress(Chamaecyparis obtusa) that are the typical Japanese forest trees. Nine major nutrients such as Na⁺, NH₄ ⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, NO₃ ^?, PO₄ ^3?, and SO₄ ^2?, were given in the water culture solution and growth of trees was observed for two years. The aspects of nutrient uptake by these seedlings and the effects of acidity in culture solution were observed. The following results were obtained. 1) Japanese cedar of 50% and Japanese cypress of 30 % in tested seedlings could live for two years. 2) All Japanese cedar and cypress that started in the strong acidic condition ( pH=3.0) were dead within three months. 3) The minimum pH value in the acidic condition is estimated as 3.2 for these coniferous seedlings, and it means that they can live at least for two years in this condition. 4) The seasonal pattern of the uptake of nitrogen nutrient by Japanese cedar was determined.     

Estimation of source-receptor matrices for deposition of NOx-N

The contributions of the anthropogenic sources of NO_x from various combinations of contiguous U.S. states or Canadian provinces to integrated deposition across selected states or provinces are estimated with the Advanced Statistical Trajectory Regional Air Pollution (ASTRAP) model. The model assumes linearity between emissions and deposition, and uses the same parameterization methods, although with different rates, as in simulations of transport and deposition of SO_X. Vertical distributions of emissions for the two classes of pollutants are substantially different in the gridded inventories used in simulations, with a weighted mean effective emission height of 160 m for NO_X and 310 m for SO_X. This might be expected to lead to an effective transport distance before deposition shorter for NO_X than for SO_X. However, the calculated fraction of NO_X emissions deposited within the contiguous United States and Canada south of 60 deg N (57%) is not greatly different from the fraction calculated for SOX emissions (54%). This suggests that there may be compensating factors in the horizontal distribution of NO_X emissions, and in the lower dry deposition velocities for NO/NO₂ than for SO₂ in ASTRAP.     

Average critical loads for nitrogen and sulfur and its use in acidification abatement policy in the Netherlands

Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO₃ pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol _c ha^?1 yr^?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol _c ha^?1 yr^?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha^?1 yr^?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol _c ha^?1 yr^?1 has been set in the Netherlands from which the N input should be less than 1000 mol _c ha^?1 yr^?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO₂, NO _x and NH₃ in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.     

Kinetic and Product Studies of the Reactions of NO2, with Hg0 in the Gas Phase in the Presence of Titania Micro-Particle Surfaces

As global mercury emissions from coal fire power plants increase with the continuing rise of coal consumption, mercury capture methods are being developed to prevent mercury??s escape into the atmosphere. Titanium dioxide (TiO₂) in the presence of ultra violet light (UV-A; ?? _max ??360?nm) and oxygen will capture mercury as the solid product HgO_(s). Testing the effects of TiO₂ in the presence of other pollutants has so far been limited. We have performed kinetic and product studies of mercury adsorption in the presence of the gaseous flue co-pollutant NO_2(g). We extensively studied the gas-phase reaction of NO₂(g) with Hg _(g) ⁰ . We compared the gas-phase reaction to the same reaction performed in the presence of thin TiO₂ particle surfaces from 0 to 100?% relative humidity. The second-order rate constant was measured to be k?=?(3.5?±?0.5)?×?10^?35?cm⁶ molecules^?2?s^?1, independent of the presence of titania or the total surface area available for adsorption. Exposure of NO_2(g) to titania surfaces that were already saturated in captured mercury (HgO_(s)) increased total mercury uptake onto the surface. We discuss the implications of this study to the capture of mercury emissions prior to release to the atmosphere.     

Hydroxyl release by maize (Zea mays L.) roots under acidic conditions due to nitrate absorption and its potential to ameliorate an acidic Ultisol

Purpose

Hydroxyl ion release by maize (Zea mays L.) roots under acidic conditions was investigated with a view to develop a bioremediation method for ameliorating acid soils in tropical and subtropical regions.

Materials and methods

Two hydroponic culture experiments and one pot experiment were conducted: pH, nitrogen state, and rhizobox condition, which investigated the effects of different nitrogen forms on hydroxyl release by maize roots under acidic conditions.

Results and discussion

The pH of the culture solution increased as culture time rose. The gradient of change increased with rising NO₃ ^?/NH₄ ⁺ molar ratios. Maize roots released more hydroxyl ions at pH 4.0 than at pH 5.0. The amount of hydroxyl ions released by maize roots at a constant pH was greater than those at a nonconstant pH. Application of calcium nitrate reduced exchangeable acidity and increased the pH in an Ultisol rhizosphere, compared with bulk soil. The increasing magnitude of soil pH was greater at higher doses of N. The absorption of NO₃ ^?–N increased as the NO₃ ^?/NH₄ ⁺ molar ratios rose, which was responsible for hydroxyl ion release and pH increases in culture solutions and rhizosphere.

Conclusions

Root-induced alkalization in the rhizosphere resulting from nitrate absorption by maize plants can be used to ameliorate acidic Ultisols.     

Determination of (Nitrate + Nitrite )‐N in alkaline permanganate solutions

Abstract

The quantitative reduction of nitrate in an acid medium with reduced Fe was applied to the alkaline permanganate solution used to absorb NO and NO₂ evolved from soils during denitrification reactions. The method involves addition of H₂SO₄ to acidify the solution and ensure oxidation of nitrite to nitrate, and treatment with reduced Fe at 100°C to reduce nitrate to ammonium. The solution is made alkaline with NaOH and ammonium determined by standard distillation procedures. It is simple and precise, and applicable to nitrogen isotope ratio analysis of NO and NO₂ evolved from soils.     

Influence of soil properties on the turnover of nitric oxide and nitrous oxide by nitrification and denitrification at constant temperature and moisture

 Soils are a major source of atmospheric NO and N₂O. Since the soil properties that regulate the production and consumption of NO and N₂O are still largely unknown, we studied N trace gas turnover by nitrification and denitrification in 20 soils as a function of various soil variables. Since fertilizer treatment, temperature and moisture are already known to affect N trace gas turnover, we avoided the masking effect of these soil variables by conducting the experiments in non-fertilized soils at constant temperature and moisture. In all soils nitrification was the dominant process of NO production, and in 50% of the soils nitrification was also the dominant process of N₂O production. Factor analysis extracted three factors which together explained 71% of the variance and identified three different soil groups. Group I contained acidic soils, which showed only low rates of microbial respiration and low contents of total and inorganic nitrogen. Group II mainly contained acidic forest soils, which showed relatively high respiration rates and high contents of total N and NH₄ ⁺. Group III mainly contained neutral agricultural soils with high potential rates of nitrification. The soils of group I produced the lowest amounts of NO and N₂O. The results of linear multiple regression conducted separately for each soil group explained between 44–100% of the variance. The soil variables that regulated consumption of NO, total production of NO and N₂O, and production of NO and N₂O by either nitrification or denitrification differed among the different soil groups. The soil pH, the contents of NH₄ ⁺, NO₂ ^– and NO₃ ^–, the texture, and the rates of microbial respiration and nitrification were among the important variables. Received: 28 October 1999     

Sur une nouvelle methode de dosage du dioxyde d'azote present dans les atmospheres polluees,derivee de la methode de Griess-Saltzmann

This paper discusses a procedure involving absorption of NO₂ on triethanolamine impregnated-papers according to a recent study of Levaggi, Siu and Feldstein. The used solid surfaces are Millipore filters, first impregnated by stirring them in a solution containing triethanolamine, glycerol and acetone before drying in an oven. Storage is made in a closed glass container. For sampling, check air flow rate to be about 30 l h^?1 through filters. The sampling time depends on the actual concentration. Samples are then analyzed in a laboratory under Saltzman's colorimetric reaction. The composition of the reagents is slightly modificated (acetic acid is replaced by phosphoric acid to obtain pH 1). Color development needs 30 min and then absorbance is compared with a standardization curve built from dilute solutions of Na NO₂. Absorption efficiencies of over 95% are attained with two impregnated filters in a filter holder and at about 301 h^?1 flow rate. Stability of filters after sampling is evaluated at 2 or 3 weeks, so it is possible to store several filters before sending them (for example by mail) to the laboratory for analysis. The stoichiometric factor depends on the weight (expressed in μg) of NO₂ collected on the filters and varies between 1.0 and 0.84. To measure NO, oxidation into NO₂ is first required, for example with an O₃ lamp.     

Distribution of bacteria in a continuous-flow nitrification column

Nutrient solution containing (NH₄)₂SO₄ was supplied at a constant rate to Nitrosomonas europaea and Nitrobacter agilis growing in a column packed with glass beads. Conversion of NH₄⁺ to NO₂^? and NO₃^? was incomplete indicating that growth of the bacteria was not nutrient limited. After 7 months the column was dismantled and the arrangement of the bacteria on the beads examined using a scanning electron microscope. Nitrifying bacteria were found only in the upper regions of the column. They occurred most commonly in monolayers, less commonly in layers of about 20 cells and rarely in piles of about 100 cells in depth. Further down the column the glass beads were covered in a layer of slime and no bacteria were seen. This suggests that growth of the nitrifiers was neither controlled by diffusion of metabolites through a microbial film nor limited by competition between the bacteria for space on the surface of the glass beads.     

Nonsteady state studies of nitrification in soil: Theoretical considerations

Equations are derived for the reactions NH₄⁺ → NO₂^? → NO₃^? in a column of inert particulate material containing Nitrosomonas and Nitrobacter and through which a solution is flowing with constant flow rate. The equations are solved analytically for two different assumptions about the growth rates of the nitrifying organisms. The effects of factors such as diffusion, ion exchange and fixation of nutrients by nitrifiers are neglected. The work generalizes a paper of McLaren and corrects a second by the same author.     

A regional scale model for the calculation of episodic concentrations and depositions of acidifying components

An eulerian long-range transport model for the calculation of concentrations of SO₂, SO₄, NO _x , and NO₃ and wet and dry depositions of SO _x (sum of SO₂ and SO₄) and NO _y (sum of NO, NO₂ and NO₃) over Europe is presented. The model is developed in such a way that only routinely available, analyzed or prognostic meteorological fields are required as input data. In this way it is possible to obtain a forecast of the air quality during smog episodes. For evaluation of smog episodes the model provides a way to estimate the contributions of different sources and the effect of emission scenarios. The model has been evaluated for four winter and three summer episodes. The modeled concentrations of SO₂ and SO, are in agreement with the available measurements. A less good agreement is found for NO₂ and NO _x (sum of NO and NO₂) concentrations. For these components the model tends to underpredict the measured values.     

Effects of phosphorus addition with and without ammonium, nitrate, or glucose on N2O and NO emissions from soil sampled under Acacia mangium plantation and incubated at 100 % of the water-filled pore space

An incubation experiment was conducted to examine the effects of phosphorus (P) addition with and without ammonium, nitrate, or glucose on N₂O and NO emissions from soil taken under Acacia mangium plantation and incubated at 100 % water-filled pore space (WFPS). Additions of NO ₃ ^? stimulated the N₂O and NO emissions while NH ₄ ⁺ did not, showing that denitrification was the main process of N₂O and NO production in the study condition. When NO ₃ ^? was added with P significantly (P?<?0.05) increased N₂O emissions regardless of the ratio of the added nitrogen and carbon, suggesting that P addition stimulated denitrification activity. The activation of denitrification by P addition is possibly attributed to two mechanisms: (1) the added-P stimulated denitrification by relieving P shortage for denitrifying bacteria and (2) the added-P stimulated activity of heterotrophic soil microflora with increased O₂ consumption promoting the development of anaerobic conditions with stimulation of denitrification.