Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Netzer, D.W. Second Reader: Shreeve, R.P. "September 1990." Description based on title screen as viewed on December 17, 2009. DTIC Identifier(s): Nitrogen oxide, NOx control, gas turbine combustors, gas turbine fuel additives, soot control, pollution control. Author(s) subject terms: NOx control, gas turbine combustors, gas turbine fuel additives, soot control, pollution control. Includes bibliographical references (p. 65-66). Also available in print.

Human activities have doubled the loading of ecosystems with reactive nitrogen (N) contributing to many serious problems such as eutrophication, climate change and pollution. As most anthropogenic reactive N is created to supply plant-available N in agriculture, one of the ways to mitigate the situation is to improve N use efficiency in crop production. It is also potentially more sustainable to supply N to crops using biological N fixation (BNF) rather than synthetic N fertilisers, because BNF does not rely on energy from fossil fuels to create plant-available N. Soil pH affects N transformations (e.g. nitrification is generally slower in low pH), but pH effects during decomposition of green manure and pH interactions with physico-chemical properties of the plant material are not well known. Here, effects of soil pH on N release, mineral-N dynamics and N2O emissions during plant material decomposition were studied. One of the objectives was to establish if regulation of soil pH could be used to manipulate N supply from green manures to crops. It was the first time such study was conducted using a long-term pH gradient (Woodlands Field, Craibstone, Aberdeen, UK). This enabled to avoid short-term effects of pH change on soil biochemical processes and confounding effects of other variables, such as soil texture and organic matter content, which vary when soils from different locations are used. Field and laboratory experiments showed that soil acidification is unlikely to be useful as a means regulate N supply from green manure (e.g. to reduce risk of nitrate leaching) as it did not significantly affect N release and nitrate dynamics. Comparison of different green manure species showed that tannin-rich plant material and purified tannins can interact with soil pH affecting soil microbial community composition and N2O emissions, but the effects were not related causally, which warrants further investigation.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Field and laboratory studies were performed to estimate fluxes of the a-ace gases nitrogen monoxide (NO), nitrous oxide (N2O), and methane (CH4) in an organic soil, to determine the microbial processes involved, and to assess how soil water and nitrogen controlled flux rates. Metabolic inhibitors showed microbial nitrification to be the major NO source, regardless of the soil moisture content. Nitrification also produced N 2O, but denitrification losses of this gas from flooded, anaerobic soil were much higher. Up to 26% of nitrified N was converted to NO, but most of this (95%) was consumed microbially before it could escape across the soil surface. The NO-consuming process appeared to be co-oxidation by soil heterotrophs, not coupled to energy production. Organic matter content and CO2 production were therefore good predictors of NO oxidation rates across soil types, and NO oxidation was stimulated by manure addition. / Soil water and nitrogen had nonlinear effects on trace gas fluxes, acting on both production and consumption. Kinetic analysis showed that nitrate was a weak noncompetitive inhibitor, but ammonium a strong competitive inhibitor of soil CH4 oxidation at field fertilization rates. However, spatial and temporal factors complicated fertilization effects on CH4 oxidation in situ. Ammonium was immobilized in surface soil and rapidly nitrified, limiting its inhibitory effect on CH 4 oxidation. Fertilizer N stimulated nitrification and denitrification and therefore gaseous N-oxide production, but other, unexpected fertilizer effects were also observed. Ammonium fertilizer decreased NO oxidation rates. Nitrate and other salts stimulated NO and N2O losses during nitrification, an effect apparently related to soil nitrite accumulation. / The controls exerted on trace gas fluxes by soil water were mediated primarily through diffusion rates. Oxygen diffusion controlled the balance of anaerobic (methanogenesis and denitrification) versus aerobic (CH 4 oxidation and nitrification) processes. Soil moisture content also controlled the diffusion rate of atmospheric CH4 to soil methanotrophs, and the escape of gaseous N-oxides from production sites across the soil surface.

Traditionally, agricultural nitrous oxide (N₂O) emission of New Zealand has been measured using chambers or lysimeters, and micrometeorological flux measurement experiments have been very few. Since micrometerological flux measurement systems have the advantage of measuring spatially integrated flux values for longer time periods compared to measurements made using chambers, development and verification of such a system was needed for New Zealand's agro-meteorological conditions. In this study, efficacy of such a combined flux gradient (FG) - eddy covariance (EC) micrometeorological flux measurement system is verified by continuously measuring N₂O fluxes from some control and mitigated agricultural plots of New Zealand. The control fields had natural N₂O emission, whereas, the mitigated plots were treated with chemicals to reduce N₂O emission. In this combined FG-EC method, the turbulent eddy diffusivities were estimated using the Monin-Obukhov (M-O) similarity theory based parameterization (where diffusion velocity `dhp' was used) and a thermal approach (where eddy diffusivity `kht' was used) from the EC measurements. These transfer coefficients (kht and dhp) along with the measured N₂O concentration differences were then fitted to the traditional FG equation to compute final flux values. As the primary objective of this study, measured fluxes from two different seasons and from two approaches were compared for consistency and then verified against published results. Under this wider objective of verification of the FG-EC micrometeorological method of N₂O flux estimation, this research thesis addresses three key issues: (i) assessment of error propagation in the measured flux through the eddy diffusivity - to understand the random error dynamics of the system and to estimate precision of the overall method, (ii) quantification and separation of N₂O source area emission rates from adjacent plots - to identify the contribution of an individual plot to the measured flux when multi-plot fluxes were measured from sources with different biogenic characters, and (iii) quantification of the effect of animal grazing and mitigation on the measured flux and actual emission rate of N₂O - to assess robustness of the FG-EC micrometeorological system. As a fourth objective of this study, (iv) new scaling properties of a turbulence surface layer model of a convective atmosphere is investigated as an alternative to the standard M-O similarity theory, as significant questioning of the M-O theory has been reported in some recent publications. Results from the verification experiment showed that the daily measured flux values obtained from this combined micrometeorlogical system for control plots varied between 0-191.9 and 0-491.8 gN₂O-N.ha⁻¹.day⁻¹ for autumn and spring experiments, respectively, for the parameterization method. Similarly, the daily mean flux values were found to be 10.9 ± 0.98 and 11.7 ± 0.57 gN₂O-N.ha⁻¹.day⁻¹ for the autumn and spring seasons, respectively. All these values were found to be of the same order of previously reported values in the literature and found to verifying that this FG-EC system works well under a range of meteorological conditions within a defined error range. Therefore, when the propagated random error was computed in the final flux value using kht and dhp, the mean relative error in kht was found to be higher than the mean relative error in dhp, irrespective of stability. From a Monte-Carlo type simulation of the random error, it was found that the maximum error can be up to 80% for kht irrespective of stability, and 49% and 35% for dhp respectively for stable (1/L ≥ 0, where L is Obukhov length) and unstable (1/L < 0) atmosphere. Errors in the concentration differences were estimated based on the minimum resolvable estimates from the gas analyzer and the associated random errors were found to be 6% and 8% for unstable and stable conditions. Finally, the total mean random error in the N2Oflux values was found to be approximately of the order of 9% and 12% for the parameterization method for unstable and stable conditions, respectively, and 16.5% for the thermal method, irrespective of stability. Objective (ii) of this research was addressed by developing a `footprint fraction' based inverse footprint method. Results of the footprint analysis method were assessed, first, by comparing footprint fractions obtained from both an analytical footprint model and a `forward' simulation of a backward Lagrangian stochastic (bLs) model; and second, by comparing the source area emission rates of a control plot obtained from the footprint analysis method and from the `backward' simulation of the bLs model. It was observed that the analytical footprint fractions were realistic as they compared well with the values obtain from the bLs model. The actual emission rates were found to be on average 2.1% higher than the measured flux values for the control plots. On average 4.3% of the measured fluxes were found to be contributed by source areas outside of the field domain. Again, the proposed footprint method of emission rate estimation was found to work well under a wider range of atmospheric stability, as the inverse footprint model and bLs model based emission rates were found to correlate well (0.70 and 0.61 for autumn and spring, respectively) with a 99% statistical significance. Similarly when the effect of grazing on the N₂O fluxes was considered, a 90% enhancement in the flux values was observed after grazing, followed by a decreasing trend in fluxes. However, contrary to existing knowledge of mitigation of N₂O flux by an inhibitor, this study found no statistically significant effect of mitigation in the pastoral emission of N₂O. Error accumulation, lesser soil N₂O production potential and/or inefficiency of the FG-EC method was conjectured to be reason/s for such discrepancy and some alternative convective boundary layer turbulence scaling was tested. Separate field measurement data, including the vertical profile measurements of the convective boundary layer and sonic anemometer measurements within the surface layer were used for this purpose. The spectral analysis of the vertical wind component, temperature and heat flux revealed that this new model of the convective boundary layer, which explains atmospheric boundary layer turbulence in terms of some nonlocal parameters, is more suitable than the traditional Monin-Obukhov similarity theory based model of atmospheric turbulence where the atmospheric flow properties are local. Therefore, it can be concluded that this new model of turbulence might provide the framework for a newer model of flux estimation in future. Overall, the FG-EC model of N₂O flux estimation method seems to work well within a certain error range. However, more field applications of this FG-EC method are needed for different agro-meteorological conditions of New Zealand before this method is accepted as a standard method of flux estimation, particularly, inefficiency in detecting the effect of mitigation should be tested. Development of an alternative flux gradient model which includes nonlocal atmospheric surface parameters might also be considered as a future research objective.

Nitrous oxide (N???O) is a potent greenhouse gas, an important driver of climate change, and its concentration in the atmosphere is rising at an unprecedented rate. Agriculture is the leading contributor of all the anthropogenic N???O sources, and the vast majority of agricultural N???O emissions originate from soil. Of all the natural N???O emissions, two-thirds originate from soil and temperate forests contribute approximately one-sixth of the natural soil emissions. Consequently, there is great interest in understanding the soil nitrogen processes responsible for N???O production so that effective policies and management practises can be implemented to successfully mitigate climate change. The stable isotopes of nitrogen (N) and oxygen (O) in soil N???O emissions are hypothesized to be useful indicators of the biogeochemical processes that produce and consume N???O, and they may be used to apportion different environmental sources. The primary objective of this thesis was to assess the utility of ???????N and ???????O values to differentiate N???O produced by nitrification and denitrification. Most of the previous research on N???O isotopes has utilized microbial cultures of single organisms; yet natural systems contain a consortium of N-metabolizing microorganisms so the relevance of this early work to natural environments is uncertain. This thesis presents the results of experimental incubations of soil from an agricultural site and a temperate forest located within Ontario, Canada. Two well-drained soils (upland), two poorly-drained soils (wetland), and one stream sediment were incubated under varying conditions (temperature, moisture, and N-availability) to achieve a wide range in the rate of N???O production. The ???????N and ???????O values of N???O produced from the different experiments were characterized and the isotope effects (??) of N???O production were calculated. Experiments were conducted in aerobic or anoxic atmospheres to stimulate N???O formation by nitrification and denitrification, respectively. The ???????N-N???O produced by denitrification in all soils was 7???35??? lower than the ???????N-nitrate (NO??????). The ???????N-N???O produced by nitrification in the upland forest soil and the agricultural soils was 28???54??? lower than the ???????N-ammonium. Nitrification in the forested wetland soil yielded higher ???????N-N???O values (?? = ???16???), which was likely caused by an increase in the ???????N-substrate. With the exception of the latter soil, there was clear ?????N-separation between the nitrification- and denitrification-derived N???O in all soils. Consequently, ???????N values can be used to apportion different environmental sources of N???O on a site-by-site basis, provided that the rates of N metabolism are known and the isotopic endmembers are well-characterized. A novel approach was employed in this thesis to help unravel the key controls of ???????O-N???O and ???????O-NO?????? formation. Different ?????O-labelled soil waters were used to demonstrate that the abiotic exchange of oxygen atoms between water and nitrite (in equilibrium) is an important control of the ???????O-N???O formed by nitrifier-denitrification and the ???????O-NO?????? formed by nitrification. O-exchange in these incubations was highly variable between soils (37???88%) and it appeared to be rate-related. Furthermore, the ???????O value of microbial NO?????? is partially controlled by ?????O/?????O fractionation that occurs during O-exchange (equilibrium fractionation) and the uptake of molecular oxygen (O???) and water (H???O) (kinetic fractionation). This research showed that the ???????O value of microbially-produced NO?????? cannot be successfully predicted in soils based upon the commonly used ???one third, two-thirds rule???, which only takes into account the ???????O values of O??? and H???O. Successful predictions of ???????O-NO?????? using this rule appear to be fortuitous and are because of the range of ???????O-H???O at natural abundance and the magnitude of the isotope effects involved. Enzyme-catalyzed (biotic) O-exchange between water and nitrite/nitric oxide in denitrification was also quantified for the first time in soils. O-exchange during denitrification was significant and variable (39???95%), but uniquely confined to narrow ranges for each soil type. Almost complete O-exchange occurred in the well-drained agricultural and forested soils (86???95%); less O-exchange occurred in the agricultural and forested wetland soils (63???70%); and even less O-exchange occurred in the agricultural stream sediment (39???51%). The magnitude of O-exchange during denitrification was independent of soil temperature and moisture for a given soil, and it was not related to the rate of N???O production. This implies that the amount of O-exchange that occurs during soil denitrification is controlled by the dominant microbial community. For the first time, estimates of the net O isotope effect were determined for N???O production by soil denitrifiers that accounted for the complicating effects of O-exchange. The net ?????O-discrimination (N???O???NO??????) ranged between +32??? and +60???, with the exception of one treatment that was cooled (?? = +17???). The O isotope separation (??) that is actually observed in natural systems is often much lower, and in some cases negative. This is because the atomic O-exchange between water and nitrite/nitric oxide effectively diminishes the net ?????O separation between NO?????? and N???O because ???????O values of environmental water are usually lower than the ???????O values of N???O-precursors. The determinants of ???????O-N???O produced by nitrification pathways are complex and there is no holistic explanation of the O isotope dynamics in the literature. This thesis provides the first systematic model to describe ???????O-N???O formation by aerobic pathways. In addition to O-exchange between water and nitrite (at equilibrium), ???????O-N???O is controlled by ?????O/?????O fractionation that results from this O-exchange mechanism, and from fractionation that occurs during ammonia-oxidation and nitrite-reduction. Although explaining ???????O-N???O values produced by nitrification is complex, reports of nitrifier-derived ???????O-N???O in the literature and this thesis are narrowly confined between +13??? and +31??? (rel. VSMOW). This is distinct from much of the denitrifier-produced ???????O-N???O, which is often ?????O-enriched and higher than +33???. In three out of the five different soils investigated in this thesis, ???????O-N???O could be used to separate N???O formed by nitrification and denitrification. There was poor ???????O separation between nitrifier- and denitrifier-derived N???O in the well-drained soils because high amounts of biotic O-exchange and reduced O isotope separations yielded lower (predicted) estimates of denitrifier-produced ???????O-N???O. On the other hand, ???????N values could be used to apportion nitrifier- and denitrifier-derived N???O sources in these soils. Thus, stable isotope ratios of N???O are a valuable and promising tool that may help differentiate nitrifier-N???O from denitrifier-N???O in natural soil environments.

The effect of acetylene (C(,2)H(,2)) on nitrifying microorganisms and the production of nitrous oxide (N(,2)O) by the ammonia-oxidizing chemoautotroph Nitrosomonas europaea was measured in culture medium and in sterilized soil. / Acetylene strongly inhibited (K(,i) 0.66 Pa) the oxidation of NH(,4)('+) to hydroxylamine (NH(,2)OH) but not of NH(,2)OH to nitrite (NO(,2)('-)) by N. europaea. The oxidation of NH(,4)('+) to NH(,2)OH and NO(,3)('-) by the heterotrophic nitrifier, Arthrobacter sp. was not affected by C(,2)H(,2) (10 kPa). / Observed patterns of N(,2)O production by N. europaea in the presence of various combinations of NH(,4)('+), NO(,2)('-), C(,2)H(,2) and oxygen (O(,2)) supported earlier published suggestions that N(,2)O may be formed via an oxidative route from NH(,4)('+) and (or) NH(,2)OH, or via a reductive route from NO(,2)('-). The former process was O(,2)-dependent and inhibited by C(,2)H(,2), while the latter process was inhibited by O(,2) but not by C(,2)H(,2). / Sodium chlorate (NaClO(,3), 10 mM) inhibited the oxidation of both NH(,4)('+) and NO(,2)('-) in dual axenic suspensions of N. europaea and Nitrobacter winogradskyi. N. winogradskyi reduced ClO(,3)('-) to ClO(,2)('-) under both aerobic and anaerobic conditions. Evidence is presented which suggests that NH(,4)('+) oxidation is inhibited by the ClO(,2)('-) so produced.

Nitrous oxide (N2O) produced from agricultural activities must be determined if management procedures to reduce emissions are to be established. From 1994 to 1996, N20 emissions were determined under continuous corn and corn-legume rotations in different soils of Quebec. Continuous corn was studied on four sites, two from a long-term experiment, a Ste. Rosalie heavy clay (Humic Gleysol) and a Chicot sandy loam (Gray-Brown Luvisol), at 0, 170,285 and 400 kg N ha-1, and two from a corn rotation study, a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Treatments in the rotation study included no-till (NT) and conventional tillage (CT), monocropped corn, monocropped soybean-, corn-soybean; and soybean-corn-alfalfa phased rotations. Nitrogen rates of 0, 90, and 180 kg N ha-1 for corn and 0, 20, and 40 kg N ha-1 for monocropped soybean were used, and soybean/alfalfa with no fertilizer N following corn. Rates of N2O emissions were significantly affected by N fertilization, tillage and soil moisture content. Generally, N2O emissions were higher in the NT systems, with corn, and increased with increasing N rates. Increased nitrogen applications led to linear increases in N2O emission over the three years for both Ste. Rosalie (2) and Ormstown soils at a rate of 1.0 to 1.6 percent of added N. The N 2O emission rates were significantly related to soil denitrification rates, water filled pore space, and soil NH4+ and NO3-- concentrations in all three years. A corn system using conventional tillage, legumes in rotation and reduced N fertilizer would decrease N2O emission from agricultural fields.

This study investigated possible reasons for the failure of the acetylene inhibition assay of denitrification in highly reducing environments and resulted in the isolation of a denitrifying Cytophaga from soil enriched by anaerobic incubation with glucose, nitrous oxide (N(,2)O), acetylene (C(,2)H(,2)), and sulfide (S('2-)). Such soil enrichments and pure cultures of the isolated Cytophaga (Is-11) reduced N(,2)O rapidly even in the presence of a normally inhibitory concentration of C(,2)H(,2) (4 kPa), providing S('2-) was present 8.0 umol (g soil)('-1) or 0.4 umol (mL culture)('-1) . The observed reaction appears to be unique to this soil Cytophaga since other organisms tested, using the same or similar experimental conditions, failed to show this response. / The isolate was characterized, after extensive comparative studies with five Cytophaga johnsonae strains, as a pigmented, Gram-negative, non-motile, gliding filamentous bacillus. Although these features established a taxonomic link with the family Cytophagaceae, the inability of Is-11 to digest chitin and DNA base composition of about 42.5 mol% (G+C) make the organism's specific affiliation uncertain.

Thesis (M.S. in environmental engineering)--Washington State University, May 2009. / Title from PDF title page (viewed on May 21, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 87-91).