Le nitrate, source majeur d’azote pour la plupart des plantes,n’est pas seulement un élément nutritif mais est aussi une molécule signale. Il existe cependant des réponses au nitrate contrastées entre les différentes plantes supérieures. Chez Medicago truncatula, espèce modèle de la famille des légumineuses, le nitrate a un effet inhibiteur sur la croissance de la racine primaire en phase post-germinative. Une étude de génétique quantitative a montré qu’un transporteur de nitrate se situe au pic d’un QTL impliqué dans la croissance de la racine primaire. La caractérisation fonctionnelle de ce transporteur, nommé MtNRT1.3 et renommé MtNPF6.8, a montré que celui-ci est à double affinité pour le nitrate. Ce transporteur est alors susceptible de participer à l’influx de nitrate dans la plante. Après l’obtention de trois génotypes mutants RNAi stables, les expérimentations utilisant duK15NO3 ont montré que ce transporteur participe effectivement à l’influx de nitrate lié au système de transport à faible affinité inductible dans la plante (iLATS). En revanche,la mutation de MtNPF6.8 ne semble pas avoir de conséquence sur le métabolisme azoté. Par ailleurs, les études sur la croissance de la racine primaire ont permis de confirmer l’implication du transporteur sur ce caractère phénotypique. L’inhibition de croissance de la racine primaire observée sur nitrate chez le génotype sauvage est alors imputée, à l’échelle cellulaire, à une modulation de l'élongation cellulaire. La possibilité que l’ABA, hormone végétale, joue un rôle dans la médiation de cette réponse dépendant du nitrate, est fortement favorisée. L’ensemble de résultats, conforté par une étude de mutants exprimant ce transporteur chez A. thaliana, indique donc que MtNPF6.8 est un senseur de nitrate pour la plante en phase post germinative,ceci indépendamment de sa fonction de transport de nitrate. / Nitrate, a major nitrogen source for most plants, is not only anutrient but also a signaling molecule. However, there arecontrasting responses to nitrate between different higherplants. In the model legume Medicago truncatula, nitrate hasan inhibitory effect on the primary root growth in postgerminationphase. A quantitative genetic study has shownthat a nitrate transporter is localized at the peak of a QTLinvolved in the primary root growth. Functionalcharacterization of the transporter, named MtNRT1.3 andrenamed MtNPF6.8, showed that it encodes a dual affinitynitrate transporter. MtNPF6.8 is likely to participate in thenitrate influx in the plant. After obtaining three knockdownlines by RNA interference, experiments using K15NO3 showedthat this transporter is effect involved in nitrate influx relatedto the inducible low affinity transport system (iLATS).However, mutation in MtNPF6.8 does not any effect onnitrogen metabolism. In addition, studies on the primary rootgrowth have confirmed the involvement of the transporteron phenotypic trait. In wild-type plants, cortical cell sizedecreased after nitrate treatment, showing that primary rootgrowth was due to this reduced cell elongation. Thepossibility that ABA also plays a role in mediating this nitratedependent response is heavily favored. All these results,reinforced by a study of mutants expressing this transporterin A. thaliana, indicate that MtNPF6.8 is a nitrate sensor forMedicago in the post-germination phase, independently ofits nitrate transport activity.

The aim of this study was to apply a variety of investigative methods to identify the causes of elevated concentrations of nitrate reported in an unconfined aquifer around the township of Coonawarra in the South East region of South Australia. For nearly 30 years elevated nitrate concentrations have been of concern to Government Departments, however the source of these elevated nitrate concentrations remained unknown. Examination of an extensive historical water quality dataset for the study area identified that while nitrate concentrations were elevated during the late 1970s – early 1980s, they have declined since this time. The study demonstrates a variety of inherent biases that can exist within nitrate groundwater datasets, and presents methods that can be used for determining temporal trends in concentration that minimise the impacts of these characteristics. The quantification and spatial variability of diffuse recharge was investigated using groundwater tritium concentrations measured in the aquifer during the late 1970s. The modelling produced estimated recharge rates that were generally below those now adopted for the study area, and the methodology may not be appropriate in areas where high irrigation rates are occurring. The assessment of the variability of recharge illustrates that the high recharge areas corresponded to the previously identified areas of higher nitrate concentrations in groundwater. This correlation was further investigated statistically, and used a dual isotopic technique that applied the natural variability of nitrogen and oxygen isotopes (of nitrate) to source determination. The statistical approach was only able to explain 39% of the variability observed in groundwater nitrate concentrations using field observations. This approach indicated that there was a significant spatial relationship between bores located in close proximity to septic tanks and elevated nitrate concentrations in groundwater. The applications of the dual nitrate isotopic method further demonstrated that nitrate in the groundwater is from multiple sources, with septic tanks being a probable source of nitrate. This isotopic method is shown to be effective in source determination, with the results comparing well to literature and field observations. Modelling of diffuse inputs from the main landuse types supports the conclusion that the elevated nitrate levels are most likely due to localised sources. It is concluded that while high nitrate concentrations have existed within the Coonawarra area, the data interpretation methods previously used to report the ‘plume’ of nitrate contamination have over-estimated the extent of nitrate in groundwater. The elevated nitrate concentrations in the groundwater are primarily the result of anthropogenic sources (e.g. septic tanks) and natural sources (e.g. the mineralisation of soil organic nitrogen).

Au cours de ce travail, le mécanisme réactionnel de réduction des ions nitrate à une électrode de cuivre en milieu neutre a été étudié et comparé aux résultats obtenus en milieux acide et alcalin. Pour ce faire, des études avec un des intermédiaires réactionnels, les nitrites, ont également été menées. En présence d'ions nitrate, trois vagues de réduction apparaissent sur le voltampérogramme vers -0,9, -1,2 et -1,3 V/ECS. Des mesures avec une électrode tournante nous ont permis de déterminer le nombre d'électrons échangés pour chaque vague, à savoir 2 (nitrites), 6 (hydroxylamine) et 8 (ammoniaque). Ces résultats ont été confirmés par voltampérométrie cyclique. Des électrolyses prolongées ont été effectuées en présence d'ions nitrate, à trois potentiels. Les analyses par spectrométrie UV-vis ont permis de détecter la présence de nitrites, hydroxylamine et ammoniaque au sein du catholyte. L'analyse par DEMS de la phase aqueuse a mis en évidence la production de protoxyde d'azote N2O à -1,2 V/ECS. Par ailleurs, une étude a été menée afin expliquer le blocage progressif de l'électrode de cuivre observé lors de la réduction des ions nitrate dans une cellule électrochimique à un seul compartiment. Ce blocage pourrait provenir du masquage des sites d'adsorption des ions nitrate par NO, ce dernier étant produit à la contre électrode suite à l'oxydation de l'ammoniaque par les radicaux hydroxyle. Enfin, la présence systématique d'une branche inductive sur les spectres d'impédance électrochimique (SIE) relevés lors de la réduction des ions nitrate constitue la signature d'un intermédiaire adsorbé impliqué dans le processus réactionnel. Finalement, l'étude SIE sur électrode tournante nous a permis de déterminer le coefficient de diffusion des ions nitrate à 25°C, valeur sur laquelle existait une certaine confusion dans la littérature. Cette valeur a conduit à une détermination précise du nombre d'électrons échangés lors de la réduction des ions nitrate.

A nitrogen fertility study with Vaughn’s hybrid bermudagrass conducted on a Crider silt loam soil (fine, silty, mixed, active, mesic Typic Paleudalfs) over three (3) years (2008-2011) at the Highland Rim Research and Education Center near Springfield, Tennessee is evaluated in this manuscript. Nitrogen applications are evaluated in both irrigated and non-irrigated plots at five (5) different application rates: 0, 56, 112, 168, and 224 kg N ha-1. These rates are applied beginning in late April, and three (3) additional times upon harvests occurring in June, July, and August. Irrigation plots receive enough water to bring total weekly water up to 2.24 cm/plot whenever rainfall is less than that amount. Normalized difference vegetative index (NDVI) measurements are collected mid harvest and on harvest dates to investigate new nitrogen status indicators between Vaughn’s hybrid bermudagrass yields. Plant tissue samples are collected at harvest. Soil samples are collected mid harvest to investigate soil nitrate nitrogen and its relationship with bermudagrass yields. The results of the study show irrigation has no effect on yields during the period of this study. There is a significant effect resulting from the interaction between month and nitrogen application on yield. Investigation of this interaction reveals two (2) distinct periods of production potential during the growing season. A low to medium yielding period produces an average harvest yield maximum of 3.14 Mg ha-1. A medium to high yield period produces an average harvest yield maximum of 5.4 Mg ha-1. Based on an analysis of variance and mean separation, a nitrogen rate of 56 kg N ha-1 rate is recommended for harvests occurring during the low to medium yielding period, and a nitrogen rate of 113 kg N ha-1 is recommended for those occurring during the high to medium yielding period. NDVI is highly correlated with yield on date of harvest. The results also show NDVI is correlated with mid-harvest yields also, which suggests a possible development of using NDVI as a mid harvest nitrogen status indicator. The results show soil nitrate is not correlated with yield, but did indicate accumulation in the soil as the growing season progressed.

Numerical models of flow and transport are commonly applied for the sustainable management of water resources and for the selection of appropriate remediation techniques. However, these numerical models are not always accurate due to uncertain parameters and the disparity of scales across which observations are made, hydrological processes occur, and modeling is conducted. The modeling framework becomes further complex because hydrologic processes are coupled with chemical and biological processes. This dissertation focuses on the most widespread contaminants of surface and ground water, which are E. coli and nitrate, respectively. Therefore, this research investigates the linkages between bio-chemical and hydrologic processes for E. coli transport, explores the spatio-temporal variability of nitrate, quantifies uncertainty, and develops models for both E. coli and nitrate transport that better characterize these biogeochemical linkages. A probabilistic framework in the form of Bayesian Neural Networks (BNN) was used to estimate E. coli loads in surface streams and was compared with a conventional model LOADEST. This probabilistic framework is crucial when water quality data are scarce, and most models require a large number of mechanistic parameters to estimate E. coli concentrations. Results indicate that BNN provides better characterization of E. coli at higher loadings. Results also provide the physical, chemical, and biological factors that are critical in the estimation of E. coli concentrations in Plum Creek, Texas. To explore model parameters that control the transport of E. coli in the groundwater (GW) and surface water systems, research was conducted in Lake Granbury, Texas. Results highlight the importance of flow regimes and seasonal variability on E. coli transport. To explore the spatio-temporal variability of nitrate across the Trinity and Ogallala aquifers in Texas, an entropy-based method and a numerical study were employed. Results indicate that the overall mean nitrate-N has declined from 1940 to 2008 in the Trinity Aquifer as opposed to an increase in the Ogallala Aquifer. The numerical study results demonstrate the effect of different factors like GW pumping, flow parameters, hydrogeology of the site at multiple spatial scales. To quantify the uncertainty of nitrate transport in GW, an ensemble Kalman filter was used in combination with the MODFLOW-MT3DMS models. Results indicate that the EnKF notably improves the estimation of nitrate-N concentrations in GW. A conceptual modeling framework with deterministic physical processes and stochastic bio-chemical processes was devised to independently model E. coli and nitrate transport in the subsurface. Results indicate that model structural uncertainty provides useful insights to modeling E. coli and nitrate transport.

The increased use of both organic and synthetic fertilizers on agricultural land has lead to rising groundwater nitrate concentrations in some areas of southern Ontario. This has occurred at the Thornton Well Field in Oxford County, likely as a result of impacts from legacy agricultural activities in the area. In an attempt to mitigate the impact on water quality within the well field, the County purchased some of the agricultural land in the vicinity of the well field in 2001 with plans to reduce nutrient loading through the implementation of Beneficial Management Practices (BMPs). Since the initiation of the BMPs, the nitrogen application rates within the study site were reduced by 20 to 100% relative to historical rates. The objectives of this study were to provide a unique, five year data set which can assist in BMP development and provide direction for regional scale agricultural policy; evaluate the nitrate mass flux at numerous locations through the unsaturated zone beneath a BMP-activated agricultural field within a complex moraine environment; develop and compare various methods to upscale point measurements of mass flux to mass loading (t N03-N/yr) at the field and regional scale; evaluate standardized methods of assessing aquifer vulnerability and compare results within the context of non-point source agricultural contaminants at the field and regional scale; and determine whether monitoring water levels and temperature within monitoring wells is able to aid in evaluating vulnerability to surface contaminants. Information collected over two years was combined with data gathered by former researchers at the field site to create a unique and extensive data set. Nineteen new monitoring wells, including two Continuous Multilevel Tubes (CMT), were installed to further develop the geological conceptual model and identify crucial discontinuities in the aquitard units. This network was devised and installed by a team of hydrogeologists. Eight geologically and topographically diverse monitoring locations or “stations” had been previously established and monitored by Bekeris (2007) to track changes in soil nitrate mass within the unsaturated zone through successive geologic coring. This study involved the selection of seven new locations that were predicted to behave similarly to one of the original eight stations in order to assess the predictive capability of scaling up point measurements. The upscaling criteria were based primarily on near surface geology, topography and field observations, with the former being determined as exerting the greatest influence on the results. Recharge rates estimates were combined with unsaturated zone soil nitrate data obtained from geologic coring events to produce nitrate mass flux estimates. Four methods of scaling up point estimates of mass flux made at fourteen of the stations to produce mass loading estimates across the whole field site were compared. The best method displayed nitrate mass loading having decreased within Parcel B from 6.77 t/yr in May 2006 to 2.55 t/yr in May 2008 resulting in a total mass reduction rate of 4.20 t/yr or 62 % which verifies the effectiveness of the BMPs. This corresponds well with the 46% decrease in applied nitrogen associated with the BMP. Groundwater quality measured using standard monitoring wells with long screens indicated that nitrate concentrations have ceased to increase, while groundwater taken from the discrete sampling ports of the CMT wells shows significantly lower concentrations of nitrate within the ports located closer to the water table. This further validates the success of the BMPs but suggests that there is a long lag time between BMP implementation and the flushing of deeper aquifer zones with cleaner, recharging water. Despite the decrease in applied nitrogen, crop yields have remained at or above historical values. Three commonly applied vulnerability assessment methods including the Aquifer Vulnerability Index (AVI), Intrinsic Susceptibility Index (ISI) and Surface to Aquifer Advection Time (SAAT) were utilized to rank the vulnerability of the Thornton Well Field to surface contaminants. The results highlighted how complex hydrogeology may result in inconsistent rankings of vulnerability by each of the methods. The results from analyzing temperature and pressure data collected from pressure transducers within wells across the site suggest that these data can verify and improve the results from standardized vulnerability assessment techniques, especially during highly vulnerable snow melt events.

The increased use of both organic and synthetic fertilizers on agricultural land has lead to rising groundwater nitrate concentrations in some areas of southern Ontario. This has occurred at the Thornton Well Field in Oxford County, likely as a result of impacts from legacy agricultural activities in the area. In an attempt to mitigate the impact on water quality within the well field, the County purchased some of the agricultural land in the vicinity of the well field in 2001 with plans to reduce nutrient loading through the implementation of Beneficial Management Practices (BMPs). Since the initiation of the BMPs, the nitrogen application rates within the study site were reduced by 20 to 100% relative to historical rates. The objectives of this study were to provide a unique, five year data set which can assist in BMP development and provide direction for regional scale agricultural policy; evaluate the nitrate mass flux at numerous locations through the unsaturated zone beneath a BMP-activated agricultural field within a complex moraine environment; develop and compare various methods to upscale point measurements of mass flux to mass loading (t N03-N/yr) at the field and regional scale; evaluate standardized methods of assessing aquifer vulnerability and compare results within the context of non-point source agricultural contaminants at the field and regional scale; and determine whether monitoring water levels and temperature within monitoring wells is able to aid in evaluating vulnerability to surface contaminants. Information collected over two years was combined with data gathered by former researchers at the field site to create a unique and extensive data set. Nineteen new monitoring wells, including two Continuous Multilevel Tubes (CMT), were installed to further develop the geological conceptual model and identify crucial discontinuities in the aquitard units. This network was devised and installed by a team of hydrogeologists. Eight geologically and topographically diverse monitoring locations or “stations” had been previously established and monitored by Bekeris (2007) to track changes in soil nitrate mass within the unsaturated zone through successive geologic coring. This study involved the selection of seven new locations that were predicted to behave similarly to one of the original eight stations in order to assess the predictive capability of scaling up point measurements. The upscaling criteria were based primarily on near surface geology, topography and field observations, with the former being determined as exerting the greatest influence on the results. Recharge rates estimates were combined with unsaturated zone soil nitrate data obtained from geologic coring events to produce nitrate mass flux estimates. Four methods of scaling up point estimates of mass flux made at fourteen of the stations to produce mass loading estimates across the whole field site were compared. The best method displayed nitrate mass loading having decreased within Parcel B from 6.77 t/yr in May 2006 to 2.55 t/yr in May 2008 resulting in a total mass reduction rate of 4.20 t/yr or 62 % which verifies the effectiveness of the BMPs. This corresponds well with the 46% decrease in applied nitrogen associated with the BMP. Groundwater quality measured using standard monitoring wells with long screens indicated that nitrate concentrations have ceased to increase, while groundwater taken from the discrete sampling ports of the CMT wells shows significantly lower concentrations of nitrate within the ports located closer to the water table. This further validates the success of the BMPs but suggests that there is a long lag time between BMP implementation and the flushing of deeper aquifer zones with cleaner, recharging water. Despite the decrease in applied nitrogen, crop yields have remained at or above historical values. Three commonly applied vulnerability assessment methods including the Aquifer Vulnerability Index (AVI), Intrinsic Susceptibility Index (ISI) and Surface to Aquifer Advection Time (SAAT) were utilized to rank the vulnerability of the Thornton Well Field to surface contaminants. The results highlighted how complex hydrogeology may result in inconsistent rankings of vulnerability by each of the methods. The results from analyzing temperature and pressure data collected from pressure transducers within wells across the site suggest that these data can verify and improve the results from standardized vulnerability assessment techniques, especially during highly vulnerable snow melt events.

The export of nitrogen (N) and phosphorus (P) from agricultural catchments is a major problem worldwide. The export of these nutrients is largely driven by storm events, and the hydrologic response of catchments varies within and between storm events. Antecedent soil moisture and rainfall rates have both been shown to affect the discharge and nutrient export from agricultural catchments, but their relationship to nutrient export is not fully understood. Currently, there are no studies that examine the leaching of both nitrate and phosphate from soil pools under the combined influence of differences in soil moisture and rainfall rates. The objectives of this study were to examine the combined effect of antecedent soil moisture and rainfall rates on the hydrologic response of soil and the export of nitrate and phosphate from the soil. The approach used intact soil monoliths in two experiments to first characterize the hydrologic response of the soil, and secondly to assess how the hydrologic response of the soil affects the leaching of nitrate and phosphate from soil pools. Differences in antecedent soil moisture and rainfall rates influenced both the amount of discharge and the hydrologic flow paths in the soil. As was expected, antecedent soil moisture governed the depth of discharge, with more discharge (runoff ratios= 0.89 to 0.91) produced by wet soil and the least runoff produced by dry soil (runoff ratios= 0.08 to 0.14) although this was not affected by the rainfall rate. Instead, rainfall rates predominantly affected hydrologic flow paths in the soil, with preferential flow at the beginning of the leaching period under high intensity rainfall (especially in wet soil), and predominantly matrix flow occurring under low intensity rainfall. The rainfall intensity did not appear to affect discharge volume. The mass of both nitrate and phosphate exported was higher under low intensity rainfall, ranging from 11.2 to 60.1mg/mU+00B2 and 77 to 4980μg/mU+00B2, respectively and from 0.9 to 34.4mg/mU+00B2 and 18.4 to 732μg/mU+00B2, respectively under high intensity rainfall. Antecedent soil moisture was significantly positively correlated with the depth of discharge produced, which also had a significant positive relationship with the mass of nitrate and phosphate exported (Spearman’s ρ= 0.75 to 0.81, p= <0.001), with greater masses of both nutrients exported from wet soil than dry soil. Soil moisture had contrasting influences on the nitrate concentrations in leachate, where nitrate concentrations and soil moisture were negatively related under low intensity rainfall and positively related under high intensity rainfall. Concentrations of phosphate in leachate were more variable, with no clear relationship to soil moisture, discharge, rainfall rate or soil phosphate pools. Antecedent soil moisture and the rainfall rate have a combined influence on the concentration of nitrate in leachate and an influence on the mass of both nitrate and phosphate exported. Although different hydrologic flow paths (matrix, preferential) were observed under the variable antecedent conditions and rainfall rates, this did not appear to affect nutrient fluxes from soil. This may be related to available nutrient pools and distributions in the soil in the current study. Understanding of the influence of flow types on the export of soil nutrient pools requires further study in a lab and a comparison of the breakthrough of nitrate and phosphate from soil pools with that of a conservative tracer (chloride). Nutrient and tracer breakthrough could then be compared to the hydraulic conductivity of the soil and the progression of the wetting front to fully understand the flow paths occurring and their effect on nutrient leaching.

In the U.S. Chemical Safety and Hazard Investigation Board (CSB) report, Improving Reactive Hazard Management, there are 37 out of 167 accidents, which occurred in a storage tank or a storage area. This fact demonstrates that thermal runaway problems in chemical storage processes have not been give enough attention. Hydroxylamine Nitrate (HAN) is an important member of the hydroxylamine compound family and its diluted aqueous solution is widely used in the nuclear industry for equipment decontamination. It is also used as a solid or aqueous propellant. Due to its instability and autocatalytic behavior, it has been involved in several incidents at the Hanford and Savannah River Sites (SRS). Much research has been conducted on HAN in different areas, such as combustion mechanism, decomposition mechanism, and runaway behavior. However, the autocatalytic behavior of HAN at runaway stage has not been fully addressed due to its highly exothermic and rapid decomposition behavior. This work focuses on extracting its autocatalytic kinetics mechanism and studying its critical behavior from adiabatic calorimetry measurements. The lumped autocatalytic kinetics model, the associated model parameters and HAN critical condition are determined for the first time. The contamination effect of iron ions and nitric acid on diluted hydroxylamine nitrate solution is also studied. This work also identified the safe storage conditions for a small quantity HAN diluted solution with thermal explosion theory. Computational Fluid Dynamics (CFD) was used to further study the influence of natural convection and system scale on the critical behavior for a large quantity of chemical and thus proposed the practical storage guidelines for industrial practice.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvi, 176 p.; also includes graphics (some col.). Includes abstract and vita. Advisor:, Dept. of Biochemistry. Includes bibliographical references (p. 168-176).