Nitrous oxide (N2O) is a powerful greenhouse gas and a major contributor to ozone layer depletion. The application of nitrogenous fertilisers to agricultural soils is a major source of N2O on a global scale. Arable soils receive significant rates of synthetic nitrogen (N) and thus have a considerable N2O footprint. The reduction of the N2O footprint of agricultural systems is a key target for those countries that seek to reduce their contribution to climate change and achieve a more sustainable agriculture. These twin targets are part of Scotland's agro-environmental policy. Because soil N2O emissions vary significantly both temporally and spatially, measuring N2O emissions across wide agricultural areas is impractical. However, the quantification of the N2O footprint of important agricultural regions is very valuable to scientists, farmers and policymakers alike. In this context, agro-ecosystem biogeochemistry models are scientific tools, which are developed using in-depth knowledge on the underlying processes, and are used to quantify N2O emissions across spatial and temporal scales. In Scotland, arable agriculture is concentrated at the Eastern part of the country where wheat, barley and oilseed rape are the most widely cultivated crops. The main aim of this study was to quantify the amount of N2O that is emitted from arable soils due to the cultivation of these three crops in Eastern Scotland by using the Landscape-DNDC model. Landscape-DNDC is a mechanistic biogeochemistry model that describes the flows of energy, water and nutrients in agricultural ecosystems. As part of the study, the parametric sensitivities of key model outputs have been quantified using well-established sensitivity analysis methods, which were tailored in order to consider the particularities of N cycling in arable soils. Driven by the fact that the existence of spatiotemporal uncertainties around field-measured soil N2O data complicates the evaluation of model performance, a novel model evaluation algorithm has been developed and was used to assess the model's predictive accuracy. By combining the knowledge of the model's parametric sensitivity with the abilities of the evaluation algorithm, nine key parameters of Landscape-DNDC were calibrated to UK edaphoclimatic conditions (using the Metropolis-Hastings Bayesian calibration algorithm). Model calibration led to improved prediction of field-measured soil N2O emissions at a set of sites. The model was then coupled to geographically explicit data on climate, soil N2O and crop management and used to simulate N2O emissions from the arable soils of Eastern Scotland. The results show that, on average, 0.59 % of the applied fertiliser N (kg N ha-1) was lost to the atmosphere as N2O. This factor is much lower than the generic N2O emission factor (EF) of 1% and closer to the UK cropland-specific N2O EF (i.e. 0.79%). The predicted annual N2O was the combined result of different drivers (i.e. fertiliser rate, soil and climate variables) but the geographic distribution of the estimated N2O EFs revealed some hotspots of high N2O EF (larger than 1%). Interestingly, these hotspots were caused by the cultivation of winter oilseed rape on soils with high bulk density and clay content. The comparison of the simulated yields per hectare with respective measured data and of the simulated nitrate (NO-3 ) leaching and crop N uptake factors with respective literature-based values showed that the prediction of soil N2O was not made at the expense of realistic prediction of other important aspects of agro-ecosystem biogeochemistry. Also, the study found that the simulated N2O is almost twice as sensitive to soil input uncertainty as the simulated NO-3 is, while, crop N uptake is rather insensitive to this source of uncertainty. Finally, the study shows that the uncertainty around the nine calibrated model parameters affects the prediction of NO-3 leaching strongly but its role in regards to the simulation of N2O emissions is small.

No description available.

Nitrous oxide (N2O) oxidizes vitamin B12. disrupting deoxyribonucleic acid (DNA) synthesis. Occupational exposures to subanesthetic levels of the gas have been documented that may result in suppressed proliferative cell activities. Male CD-I mice were exposed to 0, 50, 500, and 5000 parts of N2O per million parts of air (ppm) for 6 hr/day, 5 days/week for 2 and 13 weeks. Splenic lymphocytes were assayed for responsiveness to mitogens and for the ability to produce interleukin-2 (lL-2) . Tritiated-thymidine ([3H]-TdR) uptake was measured in CD-I splenic lymphocytes cultured in a mixed-lymphocyte culture (MLC). Cytolytic cell activity was measured by 51chromium release assay. Antibody-mediated immunocompetency was determined for sheep red blood cell (SRBC)-sensitized animals by plaque-forming cell (PFC) assay and sera anti-SRBC antibody titer. Deoxyuridine suppression tests (dUdRST) were performed on bone marrow cells. Serum adrenocorticotropic hormone and corticosterone levels were determined. There was significantly decreased splenic lymphocyte uptake of [3H)-TdR by cells cultured with mitogenic substances and in MLC following 2-week animal exposures to 5000 ppm. After 13-week exposures, the animals' splenic lymphocytes showed decreased [3H]-TdR uptake following low N20 dosing and nonsignificantly increased responsiveness at the higher gas exposures in both the blastogenic and MLC assays. Compared to control animals, the 5000- ppm-exposure group had significantly depressed PFC activity and circulating anti-SRBC immunoglobulin M levels following 13-week gas exposures, and all three subchronic exposure groups demonstrated both decreased liver weights and leukopenia. Bone marrow activity at these dosing levels was dose-responsively depressed following subchronic gas exposures.No hormonal effect appears to be attributable to N20 exposure.

Despite the spatial significance of Canadas boreal forest, there is very little known about greenhouse gas emissions within it. The primary objective of this project was to study the atmosphere-soil exchange of CH4 and N2O in the boreal forest of central Saskatchewan. In the summers of 2006 and 2007, greenhouse gas emissions were measured along transects in three different mature forest stands (trembling aspen, black spruce and jack pine) using a sealed chamber method. In addition, the gross rates of mineralization and nitrification, and the relative contribution of nitrification and denitrification to N2O emissions, were measured at the trembling aspen site using a stable isotope technique in which 15N-enriched nitrate and ammonium were injected into intact soil cores. The amount of 14N found in the labeled pools was used to measure the gross rates, and the amount of 15N found in the emitted N2O was used to determine the relative contribution of the different N pathways to total N2O emissions. Results indicated that the jack pine and black spruce sites were slight sinks of CH4 (-1.23 kg CH4-C ha-1 yr-1and -0.17 kg CH4-C ha-1 yr-1 respectively in 2006 and -0.95 kg CH4-C ha-1 yr-1and 0.45 kg CH4-C ha-1 yr-1 respectively in 2007), whereas the trembling aspen site was a net source (46.7 kg CH4-C ha-1 yr-1 in 2006 and 196.0 kg CH4-C ha-1 yr-1 in 2007). All three sites had very low cumulative N2O emissions, ranging from -0.02 to 0.14 kg N2O-N ha-1 yr-1 in both years. Of the environmental controls examined for CH4, consumption at the jack pine site was correlated positively with organic carbon and negatively with water-filled pore space. Black spruce CH4 emissions were correlated negatively with both organic carbon and clay content, and emissions at the trembling aspen site were positively correlated with soil temperature and organic carbon, while also related to the presence of standing water (2006 and 2007 had very high precipitation, causing a high water table and ponding in depressions). The N2O emissions were not correlated with any of the environmental parameters measured at the jack pine or black spruce sites, but clay content was positively related to emissions at the trembling aspen site. The 15N results indicated that N cycling at the trembling aspen site was very rapid, allowing little N to escape the system as N2O; the majority of emissions that did occur were due to a nitrification-related process.

Nitrate (NO3) contamination in agricultural watersheds is a widespread problem that threatens local drinking supplies and downstream ecology. Dual isotopes of NO3- (d15N and d18O) have been successfully used to identify sources of NO3 contamination and nitrogen (N)-cycle processes in agricultural settings. From 1998 to 2000, tile drainage and stream waters at the Strawberry Creek Catchment were sampled for NO3- concentration and isotopes. The results suggest that tile NO3 were mainly derived from soil organic matter and manure fertilizers, and that they were not extensively altered by denitrification. NO3- concentrations and isotopes in the stream oscillated between the influence of tile inputs, during periods of higher basin discharge, and groundwater inputs, during low basin discharge. The affect of denitrification was evident in stream NO3- samples. Sources and processes of dissolved NO3- and N2O were explored using concentrations and stable isotopes during the 2007 Springmelt and 2008 mid-winter thaw events. Tiles are a source of NO3- to the stream during both events and concentrations at the outflow are above the 10 mg N/L drinking water limit during the 2008 mid-winter thaw. The stream was a source of N2O to the atmosphere during both events. d15N and d18O of N2O reveal that N2O is produced from denitrification during both events. d18O:d15N slopes measured in N2O were due to the influence of substrate consumption (tiles) and gas exchange (stream). The stable isotopes of dissolved NO3- and N2O were also characterized during non-melt conditions (October 2006 to June 2007 and Fall 2007) at the Strawberry Creek catchment. Again, the purpose was to determine the sources and processes responsible for the measured concentrations and isotopic signatures. The isotope data suggests that N2O was produced by denitrification. Furthermore, NO3- consumption and gas exchange altered the original N2O signature. Isotopic distinction between soil gas N2O and dissolved N2O is suggestive of different production mechanisms between the unsaturated and saturated zones. Since the range of dissolved N2O isotopes from the Strawberry Creek catchment are relatively constraned, definition of the local isotopic signature of secondary, agricultural N2O sources was possible.

Riparian zones (RZ) are known to act as buffers, reducing the transfer of potentially harmful nutrients from agricultural fields to surface water bodies. However, many of the same processes in the subsurface that help to reduce this nutrient loading, may also be leading to greenhouse gas (GHG) production and emissions from these areas. Agricultural riparian zones in Southern Ontario are often characterized by a sloped topography, with the highest topographic position being closest to the field edge, decreasing towards an adjacent stream or other surface water body. This topographic variability, combined with lateral chemical inputs from both upland areas and the stream, is expected to cause variable hydrochemical environments throughout the RZ, which may therefore lead to variable N2O dynamics between upland, mid-riparian and lowland areas. The objectives of this study were to examine these spatial trends in N2O production and resulting emissions, as related to the hydrochemical environment in these three distinct zones. Objectives were achieved by instrumenting 6 sites across two transects running perpendicular from the agricultural field edge, towards the stream edge, analyzing for subsurface N2O, moisture and temperature, groundwater NO3, NH4, dissolved organic carbon (DOC), dissolved oxygen, and surface fluxes of N2O. Subsurface N2O concentrations and ground water nutrient concentrations displayed distinct spatial and temporal/seasonal trends in the three positions across the RZ, however N2O fluxes across the soil-atmosphere interface did not display strong or consistent spatial trends. There was a disconnect between the subsurface variables and the fluxes at the surface, in that N2O emissions did not reflect the N2O concentrations produced in the shallow soil profile (150 cm deep), nor were they significantly related to the geochemical environment at each position. The lack of visible spatial trends in N2O fluxes may have been due to an “oxic blanket” effect which may divide the surface from the subsurface soil profile. As N2O fluxes in this study (-0.28 to 1.3 nmol m-2 s-1) were within the range observed at other, similar study sites, the oxic blanket doesn’t appear to impede concentrations of N2O reaching the soil-atmosphere interface. This may suggest that the N2O released as a flux was being produced in the very shallow soil profile (0 – 5 cm), above the soil gas profile arrays installed at this site. Subsurface concentrations of N2O were fairly high at certain depths and times, which was not reflected in the fluxes. This may have resulted from nitrifier denitrification reducing N2O to N2 before it reached the surface, in aerobic zones above the water table. Another potential reason for the lack of connection between subsurface processes and surface emissions was the high heterogeneity observed across the RZ, which may have overshadowed potential differences between positions. Physical soil properties like porosity and bulk density across the RZ also potentially impacted the N2O movement through the soil profile, resulting in similar fluxes among positions, and over time. The missing connection between subsurface N2O concentrations, ground water nutrients, and the surface fluxes was not a hypothesized result, and requires further research and analysis for a better understanding of the production and consequent movement of N2O.

Nitrate (NO3) contamination in agricultural watersheds is a widespread problem that threatens local drinking supplies and downstream ecology. Dual isotopes of NO3- (d15N and d18O) have been successfully used to identify sources of NO3 contamination and nitrogen (N)-cycle processes in agricultural settings. From 1998 to 2000, tile drainage and stream waters at the Strawberry Creek Catchment were sampled for NO3- concentration and isotopes. The results suggest that tile NO3 were mainly derived from soil organic matter and manure fertilizers, and that they were not extensively altered by denitrification. NO3- concentrations and isotopes in the stream oscillated between the influence of tile inputs, during periods of higher basin discharge, and groundwater inputs, during low basin discharge. The affect of denitrification was evident in stream NO3- samples. Sources and processes of dissolved NO3- and N2O were explored using concentrations and stable isotopes during the 2007 Springmelt and 2008 mid-winter thaw events. Tiles are a source of NO3- to the stream during both events and concentrations at the outflow are above the 10 mg N/L drinking water limit during the 2008 mid-winter thaw. The stream was a source of N2O to the atmosphere during both events. d15N and d18O of N2O reveal that N2O is produced from denitrification during both events. d18O:d15N slopes measured in N2O were due to the influence of substrate consumption (tiles) and gas exchange (stream). The stable isotopes of dissolved NO3- and N2O were also characterized during non-melt conditions (October 2006 to June 2007 and Fall 2007) at the Strawberry Creek catchment. Again, the purpose was to determine the sources and processes responsible for the measured concentrations and isotopic signatures. The isotope data suggests that N2O was produced by denitrification. Furthermore, NO3- consumption and gas exchange altered the original N2O signature. Isotopic distinction between soil gas N2O and dissolved N2O is suggestive of different production mechanisms between the unsaturated and saturated zones. Since the range of dissolved N2O isotopes from the Strawberry Creek catchment are relatively constraned, definition of the local isotopic signature of secondary, agricultural N2O sources was possible.

Riparian zones (RZ) are known to act as buffers, reducing the transfer of potentially harmful nutrients from agricultural fields to surface water bodies. However, many of the same processes in the subsurface that help to reduce this nutrient loading, may also be leading to greenhouse gas (GHG) production and emissions from these areas. Agricultural riparian zones in Southern Ontario are often characterized by a sloped topography, with the highest topographic position being closest to the field edge, decreasing towards an adjacent stream or other surface water body. This topographic variability, combined with lateral chemical inputs from both upland areas and the stream, is expected to cause variable hydrochemical environments throughout the RZ, which may therefore lead to variable N2O dynamics between upland, mid-riparian and lowland areas. The objectives of this study were to examine these spatial trends in N2O production and resulting emissions, as related to the hydrochemical environment in these three distinct zones. Objectives were achieved by instrumenting 6 sites across two transects running perpendicular from the agricultural field edge, towards the stream edge, analyzing for subsurface N2O, moisture and temperature, groundwater NO3, NH4, dissolved organic carbon (DOC), dissolved oxygen, and surface fluxes of N2O. Subsurface N2O concentrations and ground water nutrient concentrations displayed distinct spatial and temporal/seasonal trends in the three positions across the RZ, however N2O fluxes across the soil-atmosphere interface did not display strong or consistent spatial trends. There was a disconnect between the subsurface variables and the fluxes at the surface, in that N2O emissions did not reflect the N2O concentrations produced in the shallow soil profile (150 cm deep), nor were they significantly related to the geochemical environment at each position. The lack of visible spatial trends in N2O fluxes may have been due to an “oxic blanket” effect which may divide the surface from the subsurface soil profile. As N2O fluxes in this study (-0.28 to 1.3 nmol m-2 s-1) were within the range observed at other, similar study sites, the oxic blanket doesn’t appear to impede concentrations of N2O reaching the soil-atmosphere interface. This may suggest that the N2O released as a flux was being produced in the very shallow soil profile (0 – 5 cm), above the soil gas profile arrays installed at this site. Subsurface concentrations of N2O were fairly high at certain depths and times, which was not reflected in the fluxes. This may have resulted from nitrifier denitrification reducing N2O to N2 before it reached the surface, in aerobic zones above the water table. Another potential reason for the lack of connection between subsurface processes and surface emissions was the high heterogeneity observed across the RZ, which may have overshadowed potential differences between positions. Physical soil properties like porosity and bulk density across the RZ also potentially impacted the N2O movement through the soil profile, resulting in similar fluxes among positions, and over time. The missing connection between subsurface N2O concentrations, ground water nutrients, and the surface fluxes was not a hypothesized result, and requires further research and analysis for a better understanding of the production and consequent movement of N2O.

Despite the spatial significance of Canadas boreal forest, there is very little known about greenhouse gas emissions within it. The primary objective of this project was to study the atmosphere-soil exchange of CH4 and N2O in the boreal forest of central Saskatchewan. In the summers of 2006 and 2007, greenhouse gas emissions were measured along transects in three different mature forest stands (trembling aspen, black spruce and jack pine) using a sealed chamber method. In addition, the gross rates of mineralization and nitrification, and the relative contribution of nitrification and denitrification to N2O emissions, were measured at the trembling aspen site using a stable isotope technique in which 15N-enriched nitrate and ammonium were injected into intact soil cores. The amount of 14N found in the labeled pools was used to measure the gross rates, and the amount of 15N found in the emitted N2O was used to determine the relative contribution of the different N pathways to total N2O emissions. Results indicated that the jack pine and black spruce sites were slight sinks of CH4 (-1.23 kg CH4-C ha-1 yr-1and -0.17 kg CH4-C ha-1 yr-1 respectively in 2006 and -0.95 kg CH4-C ha-1 yr-1and 0.45 kg CH4-C ha-1 yr-1 respectively in 2007), whereas the trembling aspen site was a net source (46.7 kg CH4-C ha-1 yr-1 in 2006 and 196.0 kg CH4-C ha-1 yr-1 in 2007). All three sites had very low cumulative N2O emissions, ranging from -0.02 to 0.14 kg N2O-N ha-1 yr-1 in both years. Of the environmental controls examined for CH4, consumption at the jack pine site was correlated positively with organic carbon and negatively with water-filled pore space. Black spruce CH4 emissions were correlated negatively with both organic carbon and clay content, and emissions at the trembling aspen site were positively correlated with soil temperature and organic carbon, while also related to the presence of standing water (2006 and 2007 had very high precipitation, causing a high water table and ponding in depressions). The N2O emissions were not correlated with any of the environmental parameters measured at the jack pine or black spruce sites, but clay content was positively related to emissions at the trembling aspen site. The 15N results indicated that N cycling at the trembling aspen site was very rapid, allowing little N to escape the system as N2O; the majority of emissions that did occur were due to a nitrification-related process.

The Gulf of Mexico hypoxic zone is created by strong persistent water stratification and nutrient loading from the Mississippi River which fuels primary production and bacterial decomposition. The Texas-Louisiana shelf becomes seasonally oxygen depleted and hypoxia (O2 less than or equal to 1.4 ml l-1) occurs. Low oxygen environments are conducive for the microbial production of nitrous oxide (N2O), a powerful greenhouse gas found in the atmosphere in trace amounts (319 ppbv). Highly productive coastal areas contribute 61% of the total oceanic N2O production and currently global sources exceed sinks. This study is the first characterization of N2O produced in the Gulf of Mexico hypoxic zone. Because of enhanced microbial activity and oxygen deficiency, it is hypothesized that the Gulf of Mexico hypoxic zone is a source of N2O to the atmosphere. Seasonal measurements of N2O were made during three research cruises in the Northern Gulf of Mexico (Sept. 2007, April 2008, and July 2008). Water column N2O profiles were constructed from stations sampled over time, and bottom and surface samples were collected from several sites in the hypoxic zone. These measurements were used to calculate atmospheric flux of N2O. The Gulf of Mexico hypoxic zone was a source of N2O to the atmosphere, and N2O production was highest during times of seasonal hypoxia. N2O was positively correlated with temperature and salinity, and negatively correlated with oxygen concentration. Atmospheric fluxes ranged from -11.27 to 153.22 umol m-2 d-1. High accumulations of N2O in the water column (up to 2878 % saturated) were associated with remineralization of organic matter at the base of the pycnocline and oxycline. Seasonal hypoxia created a source of N2O to the atmosphere (up to 2.66 x 10-3 Tg N2O for the month of September 2007), but there was a slight sink during April 2008 when hypoxia did not occur. Large fluxes of N2O during the 3 to 5 month hypoxic period may not be counterbalanced by a 7 to 9 month sink period indicating the Gulf of Mexico hypoxic zone may be a net source of N2O to the atmosphere.