This study explores the use of N2O and its isotopic composition to investigate nitrogen processes in groundwater aquifers. Groundwater sampling was undertaken in 2008-2009 at two septic system sites (Long Point site and Lake Joseph site) and two agricultural sites (Strathroy site and Woodstock site). All of these four sites have been studied previously, and denitrification zones were identified by using NO3- isotopes. Extremely broad ranges of N2O-N concentrations are present at septic system sites (1 to 1071 μg/L at Long Point and 0.1 to 106 μg/L at Lake Joseph). N2O concentrations at the agricultural sites show lower levels and narrower ranges (0.1 to 3.3 μg/L at Strathroy and 14.6 to 40.5 μg/L at Woodstock site). However, N2O-N concentrations at four sites except Strathroy are higher than the atmospheric equilibrium values (0.27 to 0.37 μg/L at 8 to 17°C) as well as N2O-N values in surface water (0.2 to 1.2 μg/L, Grand River). This provides indication of N2O production in subsurface in both septic system sites and agricultural sites. Using reported enrichment factors and measured ranges for NH4+ and NO3- isotopic values, ranges were calculated for the isotopic composition expected for N2O produced by nitrification and denitrification. At Long Point site, δ15N-N2O and δ18O-N2O ranging from -43.9 to +24.9 ‰ and +20.6 to +89.4 ‰ indicates that nitrification is mainly responsible for N2O accumulation in both proximal shallow and deep zones while some N2O at the bottom of the aquifer is presumably produced from denitrification. After N2O is produced in the plume core, δ15N and δ18O in N2O reveal that N2O is further consumed to N2. Also, N2O isotopic values cleanly show seasonal N2O production shifted from mostly nitrification in early season to primarily denitrification in late season. At Lake Joseph, δ15N-N2O and δ18O-N2O varying from -4.4 to -43.2 ‰ and +24.7 to +56.7 ‰ reveal that nitrification N2O was mainly present in aerobic zone whereas denitrification zone was found in downgradient anaerobic area. At Strathroy site, δ15N-N2O (+1.7 to -29.7 ‰) and δ18O-N2O (+33 to +65 ‰) show that N2O in shallow aquifer (< 5m depth) is presumably derived from atmosphere and nitrification whereas in deep aquifer (>5m depth), N2O formation occurs during denitrification. At Woodstock site, δ15N-N2O (-4.7 to -15.9 ‰) and δ18O-N2O (+30.7 to +37.1 ‰) at Woodstock provide indication of N2O production from a mixing of denitrification N2O and tropospheric N2O. N2O isotopic signatures are highly useful to identify N2O sources which include nitrification, denitrification, and dissolution of atmospheric N2O at both septic system sites and agricultural sites. Further, at Lake Joseph site and Woodstock site, denitrification evidence from NO3- concentration/isotopes is lacking but N2O isotopes suggest the occurrence of denitrification. At Long Point site, N2O isotopes indicated N2O production was by denitrification occurred early in the season; however, no NO3- isotopic enrichment was t that depth until in late season. These sites provide evidence that N2O is an early and sensitive indicator of denitrification in groundwater at both septic system and agricultural sites. Additionally, N2O isotopes are valuable for detecting N2O consumption whereas NO3- isotopes cannot provide insight into this process.

This study explores the use of N2O and its isotopic composition to investigate nitrogen processes in groundwater aquifers. Groundwater sampling was undertaken in 2008-2009 at two septic system sites (Long Point site and Lake Joseph site) and two agricultural sites (Strathroy site and Woodstock site). All of these four sites have been studied previously, and denitrification zones were identified by using NO3- isotopes. Extremely broad ranges of N2O-N concentrations are present at septic system sites (1 to 1071 μg/L at Long Point and 0.1 to 106 μg/L at Lake Joseph). N2O concentrations at the agricultural sites show lower levels and narrower ranges (0.1 to 3.3 μg/L at Strathroy and 14.6 to 40.5 μg/L at Woodstock site). However, N2O-N concentrations at four sites except Strathroy are higher than the atmospheric equilibrium values (0.27 to 0.37 μg/L at 8 to 17°C) as well as N2O-N values in surface water (0.2 to 1.2 μg/L, Grand River). This provides indication of N2O production in subsurface in both septic system sites and agricultural sites. Using reported enrichment factors and measured ranges for NH4+ and NO3- isotopic values, ranges were calculated for the isotopic composition expected for N2O produced by nitrification and denitrification. At Long Point site, δ15N-N2O and δ18O-N2O ranging from -43.9 to +24.9 ‰ and +20.6 to +89.4 ‰ indicates that nitrification is mainly responsible for N2O accumulation in both proximal shallow and deep zones while some N2O at the bottom of the aquifer is presumably produced from denitrification. After N2O is produced in the plume core, δ15N and δ18O in N2O reveal that N2O is further consumed to N2. Also, N2O isotopic values cleanly show seasonal N2O production shifted from mostly nitrification in early season to primarily denitrification in late season. At Lake Joseph, δ15N-N2O and δ18O-N2O varying from -4.4 to -43.2 ‰ and +24.7 to +56.7 ‰ reveal that nitrification N2O was mainly present in aerobic zone whereas denitrification zone was found in downgradient anaerobic area. At Strathroy site, δ15N-N2O (+1.7 to -29.7 ‰) and δ18O-N2O (+33 to +65 ‰) show that N2O in shallow aquifer (< 5m depth) is presumably derived from atmosphere and nitrification whereas in deep aquifer (>5m depth), N2O formation occurs during denitrification. At Woodstock site, δ15N-N2O (-4.7 to -15.9 ‰) and δ18O-N2O (+30.7 to +37.1 ‰) at Woodstock provide indication of N2O production from a mixing of denitrification N2O and tropospheric N2O. N2O isotopic signatures are highly useful to identify N2O sources which include nitrification, denitrification, and dissolution of atmospheric N2O at both septic system sites and agricultural sites. Further, at Lake Joseph site and Woodstock site, denitrification evidence from NO3- concentration/isotopes is lacking but N2O isotopes suggest the occurrence of denitrification. At Long Point site, N2O isotopes indicated N2O production was by denitrification occurred early in the season; however, no NO3- isotopic enrichment was t that depth until in late season. These sites provide evidence that N2O is an early and sensitive indicator of denitrification in groundwater at both septic system and agricultural sites. Additionally, N2O isotopes are valuable for detecting N2O consumption whereas NO3- isotopes cannot provide insight into this process.

The transfer of N from legume green manures (GMr) can satisfy the needs of a successive cash crop, but rotations that have over-wintering legumes also carry an increased risk of off-season (Sep.–June) N losses, especially during spring thaw. Spring-wheat yield among four GMr systems were evaluated with respect to off-season (GMr; Sep.–June) and in-season (wheat; June–Sep.) N2O emissions, as well as full-year NO3– leaching and dissolved N2O losses during spring-thaw from a tile-drained sandy loam soil in Atlantic Canada over 2 rotations (2011–2013). Four GMr systems (treatments) differed in the timing and season of GMr incorporation and the use of additional N as fertilizer or manure. The majority (66%) of cumulative N2O emissions were measured during the off-season because of high N2O emissions events during spring thaw. There was no clear effect of GMr system on these emissions, which may have been a result of the pattern and duration of soil freezing and thawing. Spring thaw also coincided with the highest dissolved N2O concentrations (100–300 µg N2O-N L–1) in tile-drained water, which represented potential N2O emissions of 21 to 116 g N2O-N ha–1. Belowground N2O concentrations and soil water content measurements during winter provided further evidence of the relationship of N2O dissolved in drainage water and N2O emissions at the soil surface. Wheat yield among treatments in either year of study were not different, but was 1.5 times greater in Year 2 (2.62 ± 0.27 Mg ha–1), than Year 1 (1.05 ± 0.12 Mg ha–1). The highest NO3– concentrations in drainage water (Oct.; 13.8 mg NO3–-N L–1) were measured from the GMr system with the earliest fall incorporation (i.e., Sep.) and the addition of spring fertilizer when compared to the mean of all other treatments (9.8 mg NO3–-N L–1). The use of supplemental N did not translate into additional gains in yield, yet increased in-season N2O emissions and greater NO3– leaching. Off-season N losses proved to be a substantial part of the annual N loss budget and dissolved N2O in drainage water was identified as an additional pathway for N loss at spring thaw.

No description available.

Effective control of nitrification processes employed at municipal wastewater treatment plants is essential for maintaining process reliability and minimizing environmental impacts and operating costs. While a range of process control strategies are available, they share a dependence on invasive liquid phase monitoring and are based on a periphery understanding of the metabolic status of the processes being controlled. Utilization of off-gas nitrous oxide (N2O) monitoring as a real-time indicator of the process metabolic status is a novel process control concept with the potential to address these concerns. This thesis details the development and evaluation of an off-gas N2O stress response based control technique. Examination of the stress response relationship demonstrated that it met the majority of the criteria of interest for process control. A simple feedback aeration control strategy was developed and evaluated through process simulation to determine the feasibility of implementation, cost effectiveness and associated environmental benefits. The off-gas N2O based control strategy provided better matching between aeration supply and metabolic demand, allowing the process to be maintained at the desired operating setpoints and avert nitrification failure. Performance was demonstrated to be similar to dissolved oxygen based feedback aeration control, although slightly more efficient at reduced dissolved oxygen concentrations. A technical, economic and environmental evaluation indicated that aeration control based on non-invasive off-gas N2O monitoring is technically feasible and has the potential to offer significant environmental and economic benefits including reductions in operating costs and process capital investment, as well as improved effluent compliance and reductions in emissions of gaseous pollutants including greenhouse gases. Overall, while off-gas N2O monitoring based aeration control techniques have the potential to provide significant economic and environmental benefits, a number of research questions remain to be answered. Future work in the form of long-term field trials is required to address these issues and allow quantification of economic and environmental benefits.

Abstract Methane (CH4) and nitrous oxide (N2O) are not only important but also long-lived greenhouse gases. Unfortunately, in Taiwan, although there are some data on CH4 emission from rivers and lakes there is no data about N2O emission from rivers, lakes and coasts. So this study investigated CH4 and N2O distribution in natural waters around Taiwan. In Taiwan, the average CH4 concentration in rivers is about 3082¡Ó12399nM (n=152). The average CH4 concentration in mountain lakes is about 2899¡Ó7291nM (n=51). The average CH4 concentration in lower elevation lakes and reservoirs is about 1825¡Ó2755nM ppmv (n=95). The average CH4 concentration in near-shore waters is about 36.7¡Ó285nM (n=476). The CH4 distribution is rivers> mountain lakes>low-elevation lakes and reservoirs >seawater. In southeastern China, the average CH4 concentration in rivers is about 1029¡Ó2487nM ppmv (n=36). The average CH4 concentration of samples taken from rivers in southeastern China is lower than Taiwan rivers. But the highest CH4 concentration of all samples is in Chih-Kan river of southeastern China (14914nM), due to uneven population distribution as well as different levels of development among cities and suburbs. In Taiwan, the average N2O concentration in rivers is about 32.8¡Ó69.1nM (n=58). In southeastern China, the average N2O concentration in rivers is about 29.7¡Ó9.05nM (n=36). The average N2O concentration in Taiwanese rivers is higher than found in southeastern China. This is likely because farmers in Taiwan use more synthetic fertilizers so the soil becomes full of N element, and then rivers and rains rinse the soil. This process has increased the concentration of N and N2O in rivers. In summer, the average CH4 and N2O concentrations in northern Taiwan Strait are about 3.27¡Ó2.42nM and 7.22¡Ó0.62nM (n=7), respectively; and the average CH4 and N2O fluxes are about 0.17¡Ó0.43£gmol/m2/h and 0.14¡Ó0.26 £gmol/m2/h, respectively. The average CH4 and N2O concentrations in southern Taiwan Strait are about 3.35¡Ó1.97nM and10.31¡Ó2.51nM (n=30), respectively; and the average CH4 and N2O fluxes are about 0.04¡Ó0.09£gmol/m2/h and 0.19¡Ó0.22 £gmol/m2/h, respectively. In winter, the average CH4 and N2O concentrations in northern Taiwan Strait are about 4.74¡Ó1.43nM and 8.41¡Ó0.46nM (n=9), respectively; and the average CH4 and N2O fluxes are about 0.10¡Ó0.14£gmol/m2/h and 0.008¡Ó0.033 £gmol/m2/h, respectively. The average CH4 and N2O concentrations in southern Taiwan Strait are about 4.70¡Ó2.42nM and 8.36¡Ó0.97nM (n=17), respectively; and the average CH4 and N2O fluxes are about 0.17¡Ó0.46£gmol/m2/h and 0.11¡Ó0.12 £gmol/m2/h, respectively. Taiwan Strait is a source of CH4 and N2O regardless of whether it is summer or winter. In summer, the average CH4 and N2O concentrations in the South China Sea are about 4.34¡Ó2.33nM and 8.23¡Ó1.5nM (n=55), respectively; and the average CH4 and N2O fluxes are about 0.33¡Ó0.35£gmol/m2/h and 0.20¡Ó0.24 £gmol/m2/h, respectively. It is a source of CH4 and N2O to the atmosphere. In summer, the average CH4 and N2O concentrations in the West Philippines Sea are about 3.18¡Ó1.57nM and 4.64¡Ó0.39nM (n=60), respectively; and the average CH4 and N2O fluxes are about 0.23¡Ó0.33£gmol/m2/h and -0.28¡Ó0.30 £gmol/m2/h, respectively. It is a source of CH4 but a sink of N2O to the atmosphere.

No description available.

No description available.

Effective control of nitrification processes employed at municipal wastewater treatment plants is essential for maintaining process reliability and minimizing environmental impacts and operating costs. While a range of process control strategies are available, they share a dependence on invasive liquid phase monitoring and are based on a periphery understanding of the metabolic status of the processes being controlled. Utilization of off-gas nitrous oxide (N2O) monitoring as a real-time indicator of the process metabolic status is a novel process control concept with the potential to address these concerns. This thesis details the development and evaluation of an off-gas N2O stress response based control technique. Examination of the stress response relationship demonstrated that it met the majority of the criteria of interest for process control. A simple feedback aeration control strategy was developed and evaluated through process simulation to determine the feasibility of implementation, cost effectiveness and associated environmental benefits. The off-gas N2O based control strategy provided better matching between aeration supply and metabolic demand, allowing the process to be maintained at the desired operating setpoints and avert nitrification failure. Performance was demonstrated to be similar to dissolved oxygen based feedback aeration control, although slightly more efficient at reduced dissolved oxygen concentrations. A technical, economic and environmental evaluation indicated that aeration control based on non-invasive off-gas N2O monitoring is technically feasible and has the potential to offer significant environmental and economic benefits including reductions in operating costs and process capital investment, as well as improved effluent compliance and reductions in emissions of gaseous pollutants including greenhouse gases. Overall, while off-gas N2O monitoring based aeration control techniques have the potential to provide significant economic and environmental benefits, a number of research questions remain to be answered. Future work in the form of long-term field trials is required to address these issues and allow quantification of economic and environmental benefits.

L’objectif de ma thèse est de conduire et d’utiliser les observations de haute précision de gaz à effet de serre pour estimer les émissions de ces gaz à différentes échelles en France, du locale au régionale. Le réseau français de mesure de gaz à effet de serre, géré par l’équipe RAMCES, est constitué de trois observatoires équipés de systèmes de mesure par chromatographie en phase gazeuse. Ces chromatographes en phase gazeuse sont situés à Gif-sur-Yvette, Trainou (forêt d’Orléans) et au sommet du Puy-de-Dôme. Ils ont été optimisés pour la mesure continue et de haute précision des principaux gaz à effet de serre : CO2, CH4, N2O et SF6. Ayant installé le GC au Puy-de-Dôme au cours de l’année 2010, je présenterai et analyserai en détail la série temporelle obtenue depuis son installation. Les mesures de gaz à effet de serre et des traceurs associés m’ont permis d’utiliser une approche multigaz pour contraindre leurs émissions à différentes échelles. A une échelle départementale et régionale, j’ai utilisé le 222Rn comme traceur de masses d’air pour quantifier les flux surfaciques mensuels de N2O à Gif-sur-Yvette et Trainou. Les émissions annuelles de N2O estimées à Gif-sur-Yvette et Trainou sont respectivement de 0.34/0.51 et 0.52 g(N2O) m-2 a-1. Le cycle saisonnier des émissions de N2O a permis de mettre en évidence l’impact de l’agriculture sur les émissions lors de l’apport d’engrais azoté dans les sols. J’ai mis en évidence une corrélation entre les flux de N2O annuels et les précipitations annuelles à Gif-sur-Yvette. A une échelle locale, j’ai utilisé le CO2 et ses isotopes mesurés lors d’une campagne réalisée pendant l’hiver 2010 à Paris, pour estimer les flux de CO2 parisien. Les mesures de 14CO2 atmosphérique m’ont permis de montrer que les flux de CO2 parisien en hiver sont essentiellement anthropiques (77 %) avec une contribution significative des émissions biogéniques (23 %). L’analyse du 13CO2 à quant à lui mis en évidence que les 77 % d’émission de CO2 d’origine fossile sont dues à 70 % à l’utilisation de gaz naturel et 30 % à l’utilisation de pétrole. / The aim of my PhD is to use high precision measurements to evaluate greenhouse gas emissions at different scales in France, from local to regional. These measurements are made in the framework of the French greenhouse gases network operated by the RAMCES team. Three stations in France are equipped with gas chromatography measurement systems located at Gif-sur-Yvette, Trainou (Orléans forest) and on the summit of Puy-de-Dôme. They were optimized to measure continuously with high precision the main greenhouse gases: CO2 , CH4 , N2O and SF6. In July 2010, I have installed the gas chromatograph at Puy-de-Dôme and I present here the analysis of the past two years. I used an approach with measurements of greenhouse gases and related trace gases to constrain the emissions of greenhouse gases at different scales. At a regional scale, I used the 222Rn as an air mass tracer to quantify the monthly N2O fluxes at Gif-sur-Yvette and Trainou. Annual N2O emissions, derived from the atmospheric approach at Gif-sur-Yvette and Trainou are 0.34/0.51 and 0.52 g(N2O) m−2 a−1 , respectively. I found a clear seasonal cycle of N2O emissions with larger values in spring and summer, demonstrating the large contribution of agricultural emissions from fertilized soils. A correlation between annual N2O fluxes and annual precipitations was observed at Gif-sur-Yvette. At a local scale, I used carbon isotopes to estimate the fossil fuel CO2 contribution. Measurements were performed during a campaign in winter 2010 in Paris. Atmospheric 14 CO2 measurements showed that 77 % of total CO2 emissions are anthropogenic with a significant contribution of biospheric fluxes (23 %). Additionally, 13CO2 analysis showed that natural gas and fuel combustion amounted to 70 % and 30 %, respectively, of fossil fuel emissions.