Small N2O Research Articles

Groundwater seeps are hot spots of denitrification and N2O emissions in a restored wetland

Restorations of former cranberry farms (“bogs”) aim to re-establish native wetland vegetation, promote cold water habitat, and attenuate nitrogen (N) delivery to coastal waters. It is unclear, though, how elements of restoration design such as microtopography, groundwater interception, and plant communities affect N removal via denitrification. In a recently restored riparian cranberry bog with created microtopography, we compared denitrification potential, nitrous oxide (N2O) yield of denitrification (ratio of N2O:N2O + N2 gases), in situ N2O fluxes, soil chemistry, and plant communities at the highest and lowest elevations within 20 plots and at four side-channel groundwater seeps. Denitrification potential was > 2 × greater at low elevations, which had plant communities distinct from high elevations, and was positively correlated with plant species richness (Spearman’s rho = 0.43). Despite detecting high N2O yield (0.86 ± 0.16) from low elevation soils, we observed small N2O emissions in situ, suggesting minimal incomplete denitrification even in saturated depressions. Groundwater seeps had an order of magnitude higher denitrification potentials and 100–300 × greater soil NO3− concentrations than the typically saturated low elevation soils. Groundwater seeps also had high N2O yield (1.05 ± 0.15) and higher, but spatially variable, in situ N2O emissions. Our results indicate that N removal is concentrated where soils interact with NO3–rich groundwater, but other factors such as low soil carbon (C) also limit denitrification. Designing restoration features to increase groundwater residence time, particularly in low lying, species rich areas, may promote more N attenuation in restored cranberry bogs and other herbaceous riparian wetlands.

Adsorption of small gas molecules onto boron nitride nanotubes and their Al-, Ga-, Cr- and Fe-doping derivatives for gas sensing, storage, and catalytic properties: Periodic DFT study

Based on the toxic gases and their conversion to non-toxic gases on the high potentials doping derivatives of boron nitride nanotubes (BNNTs), adsorption abilities of (5,5) and (10,0) BNNTs doped by selected dopants (Al, Ga, Cr and Fe) on small gas molecules was explored. Adsorption of small gas molecules, H2O, H2S, SO2, CO2, CO, NH3, N2O, and NO onto the pristine (5,5) and (10,0) BNNTs, their doping derivatives (Al-, Ga-, Cr- and Fe-doped (5,5) and (10,0) BNNTs) were investigated using periodic DFT method. Strong adsorptions of N2O (-4.26 eV) and SO2 (-2.56 eV) on the Cr-(5,5) and Cr-(10,0) BNNTs were found. Furthermore, the Cr-(5,5) and Cr-(10,0) BNNTs as the catalysts for N2O conversion to N2 and O2 were found. The Al- and Ga-(5,5) BNNTs, Al- and Ga-(10,0) BNNTs are suggested as the NO sensing materials and NH3 storage materials. All the suggested materials such Cr-(5,5), Cr-(10,0), Al-(5,5), Ga-(5,5), Al-(10,0) and Ga-(10,0) BNNTs could be experimentally tested for conversion, sensitivity, and storage of mentioned toxic gases in the future.

Methane and Nitrous Oxide Fluxes with Different Land Uses in the Temperate Meadow Steppe of Inner Mongolia, China

Background and aims: Grazing and mowing are widely adopted management practices for the semiarid steppe in China that profoundly affect the greenhouse gas (GHG) flux in grassland ecosystems. However, the general mechanisms for CH4 and N2O fluxes in response to grazing and mowing remain poorly understood. Thus, we conducted year-round flux measurements of CH4 and N2O fluxes to investigate the effect of grazing and mowing on CH4 and N2O fluxes. Methods: Using manual static chamber and gas chromatography, we measured the fluxes of CH4 and N2O from grazing-exclusion, grazing and mowing sites from June 2019 to June 2020 in the Hulunbuir Grassland, Inner Mongolia. Results: Grazing and mowing increased soil temperature and reduced soil water content and soil inorganic N content. Compared with grazing and mowing, lower mean CH4 uptake (−67.58 ± 8.9 μg m−2 h−1) and higher mean N2O emissions (29.17 ± 6.8 μg m−2 h−1) were found at the grazing-exclusion site. No pulse emissions of N2O were found for all sites during the spring thaw period (STP), and only two small N2O emission peaks due to soil thawing were captured on April 2nd and 5th. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 10%, 13% and 12% of the annual fluxes at the grazing-exclusion, grazing and mowing sites, respectively. Conclusion: Our results indicate that grazing and mowing enhance CH4 uptake and inhibit N2O emissions, primarily due to the increased soil temperature and reduced soil water content and soil inorganic N content. No apparent pulse N2O emissions were observed at any of the three sites during the STP in the Hulunbuir grassland.

One step closer towards a greener NHS: decommissioning of piped nitrous oxide manifolds

Background: Nitrous oxide (N2O) is a widely used anaesthetic gas that is both a powerful greenhouse agent with 298 times the global warming potential of carbon dioxide (CO2)1 and detrimental to the ozone layer. According to NHS Lothian recent investigations, massive N2O leakage from piped manifold systems has been highlighted.2 One simple solution is to decommission N2O manifolds, with small N2O cylinders on the anaesthetic machines reserved for occasional usage. Hence, this project is initiated at Perth Royal Infirmary (PRI) with the goal of decommissioning the piped N2O manifold facility to meet the NHS Scotland Zero N2O emission by year 2027. Methods: A survey was conducted among all anaesthetists in PRI Anaesthetic department to evaluate their N2O usage preference and feasibility of decommissioning the piped N2O manifold. The N2O supply data provided by the pharmacy team was over a period of 10 months for the year 2021–22. To quantify the clinical usage at PRI, we captured the cumulative N2O usage over a 20-day period, using the data obtained from the service mode on each anaesthetic machine. From there, we extrapolated and calculated the annual estimated supply, usage, and wastage amount. Results: From the survey, all anaesthetists reported that their N2O usage is very low. Seventy-one percent of anaesthetists have decreased N2O usage over the past 5 yr, and there are no objections to the decommissioning of the piped N2O manifold. Based on our calculations, only 5475 L N2O are estimated to be consumed as opposed to 126 890 L supplied per annum. This demonstrates that as much as 96% or 121 415 L N2O are wasted. Financially, this is equivalent to 13.5 size G N2O cylinders worth £3145 per annum. To put into perspective, this corresponds to 64 964 kg CO2 equivalent emission or a staggering 541 366 km of car travel. Conclusions: We found significant wastage of N2O, unnecessary long-term financial expenditure, and adverse consequences to planetary health that could all be prevented. Our next step is to execute the plan of decommissioning piped N2O manifolds in accordance with the interim protocol for decommissioning set by the Scottish Government. Although this is a small step towards a greener sustainable future, multidisciplinary efforts from all related departments are essential in making this vision a reality. Eventually, re-audit will be carried out to evaluate the outcome of this action before rolling this improvement plan out to all sites within NHS Tayside. 1.Myhre G, Shindell D, Breon FM, et al. Anthropogenic and natural radiative forcing. In: IPCC Fifth Assessment Report. 2013.2.Chakera A, Fennell-Wells A, Allen A. Nitrous oxide project: piped nitrous oxide waste reduction strategy. Association of Anaesthetists, 2021 Jan 15. Available from: https://anaesthetists.org/Home/Resources-publications/Environment/Nitrous-oxide-project.

Seasonal Variations of SF6, CO2, CH4, and N2O in the UT/LS Region due to Emissions, Transport, and Chemistry

AbstractDistributions of trace gases in the atmosphere provide key information on the transport and chemical properties of the Earth's environment. In this study, we examine the observed seasonal variability of SF6, CO2, CH4, and N2O from commercial aircraft‐based measurements in the upper troposphere and lower stratosphere (UT/LS) in combination with atmospheric chemistry‐transport model (ACTM) simulations. We used a dynamical tropopause defined based on maximum PV gradient that better allows for model‐observation comparisons in the UT and LS regions separately. The ACTM simulated the following observed features well: (1) smaller seasonality in SF6 in the UT than in the LS due to seasonal change in the transport processes, (2) large seasonality in CO2 in the UT, in phase with the source‐sink balance on the Earth's surface, (3) pronounced seasonality in CH4 in the UT with opposite phase in the subtropics and Eurasian high latitudes as contrasting phases of source and chemical loss seasonality develop, and (4) small N2O variability in the UT but stratospheric loss produces distinct seasonality in the LS. Vertical profile comparisons of all the species show that ACTM better simulated the photo‐chemically inert CO2 vertical gradients in all seasons, suggesting a realistic representation of the Brewer‐Dobson circulation in the model. The seasonal variabilities of the long‐lived species in the LS can be explained based on age of air derived from CO2 in the older air regime, except for the months of May‐July, when the model mixes UT and LS air more vigorously than suggested by the observations.

Effect of organic amendments on yield-scaled N2O emissions from winter wheat-summer maize cropping systems in Northwest China.

The effect of dairy manure amendments to agricultural soil on the yield-scaled nitrous oxide (N2O) emissions remains unclear. We hypothesize that an optimum ratio of dairy manure to synthetic fertilizers leads to large nitrogen use efficiency (NUE) and small yield-scaled N2O emissions. The aims of this study were to (1) quantify the variations in the crop yields and N2O emissions from winter wheat-summer maize cropping systems in Northwest China, (2) determine the responses of the NUE and yield-scaled N2O emission to the ratio of organic materials to synthetic fertilizers, and (3) evaluate the relationship between the NUE and yield-scaled N2O emissions. Field measurements were conducted within long- and short-term fertilization experiments between the years of 2014 and 2016. Treatments included synthetic fertilizers, synthetic fertilizers plus crop residues, and synthetic fertilizers plus dairy manure at both sites. The annual grain yields and N2O emissions varied from 13.3 to 18.0 Mg ha-1 and from 1.3 to 3.6 kg N ha-1, respectively, across the treatments. The yield-scaled N2O emissions related negatively to the NUE, suggesting that agronomic aims of improving NUE are an effective approach to mitigate N2O emissions. The ratio of organic materials to synthetic fertilizers was not a significant limit on the NUE and yield-scaled N2O emissions. We conclude that organic amendments appeared to play a minor influence on the promotion of the NUE and N2O mitigation.

Nitrogen and phosphorus cycling in the digestive system and shell biofilm of the eastern oyster Crassostrea virginica

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 621:95-105 (2019) - DOI: https://doi.org/10.3354/meps13007 Nitrogen and phosphorus cycling in the digestive system and shell biofilm of the eastern oyster Crassostrea virginica Nicholas E. Ray1,*, Maria C. Henning2, Robinson W. Fulweiler1,2 1Boston University, Department of Biology, Boston, MA 02215, USA 2Department of Earth and Environment, Boston University, Boston, MA 02215, USA *Corresponding author: nray@bu.edu ABSTRACT: The shell and digestive system of bivalves provide microhabitats for an array of microbes that can mediate biogeochemical cycles. Here, we investigated nitrogen (N) and phosphorus (P) fluxes in these microhabitats in the eastern oyster Crassostrea virginica. From the anoxic oyster digestive system, we measured significant production of dinitrogen gas (N2-N; mean ± SE: 0.59 ± 0.20 µmol ind.-1 h-1) and nitrous oxide (N2O; 0.001 ± 0.0004 µmol ind.-1 h-1), indicative of denitrification. The oxic shell biofilm released N2O (0.0003 ± 0.0001 µmol ind.-1 h-1), as well as ammonium (NH4+; 1.26 ± 0.20 µmol ind.-1 h-1) and nitrite (NO2-; 0.05 ± 0.01 µmol ind.-1 h-1), but not N2-N, suggesting a combination of nitrification and heterotrophic activity. The biofilm released more dissolved inorganic P than the digestive system, although the rate of release from whole oysters was closer to the rate from the digestive system alone. N remineralized by oysters is released almost exclusively as NH4+, at a ratio of 18.4:1 with P, i.e. relatively close to the Redfield ratio (16:1). In an ecological context, this study supports the growing literature on the ability of oysters themselves to engage in denitrification activity and at rates potentially exceeding rates of sediment denitrification. The denitrification in the digestive system appears to proceed to completion and has a very small N2O cost (<1%). Restoring oyster populations may therefore be an important method for N reduction in coastal systems. KEY WORDS: Oyster · Nitrogen · Denitrification · Nitrous oxide · Nitrification · Shellfish Full text in pdf format Supplementary material PreviousNextCite this article as: Ray NE, Henning MC, Fulweiler RW (2019) Nitrogen and phosphorus cycling in the digestive system and shell biofilm of the eastern oyster Crassostrea virginica. Mar Ecol Prog Ser 621:95-105. https://doi.org/10.3354/meps13007 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 621. Online publication date: July 04, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Greenhouse Gas Production and Transport in Desert Soils of the Southwestern United States

AbstractDeserts comprise a large portion of the Earth's land area, yet their role in the fluxes and cycles of greenhouse gases is poorly known and their likely response to climate change largely unexplored. We report a reconnaissance investigation of the concentrations and fluxes of CO2, CH4, and N2O along two elevation (climate) gradients in the southwestern United States. In‐soil concentrations of CO2 increased with elevation (up to 5,000 ppm). Concentrations of CH4 declined with depth in all soils (to less than 1 ppm), but the rates of decrease with depth increased with elevation. In contrast, concentrations and depth trends of N2O varied erratically. Soils were net CO2 sources (0 to &gt;1,500 kg CO2·ha−1·year−1), and net CH4 sinks (0.2 to &gt;3 kg CH4·ha−1·year−1). The small and variable N2O fluxes were inconsistent with the trends in soil N δ15N values, which decreased by 5‰ to 6‰ over about 1,000 m of elevation. The high soil N δ15N values (up to nearly 17‰ at the lowest elevation) indicate that there is a soil N loss mechanism that is highly depleted in 15N, and gaseous losses—either NH3 or N2O/N2—are suspected of driving these values. In summary, there appears to be a strong climate control on both soil CO2 and CH4 concentrations and to a lesser degree on calculated fluxes. The soil N trace gas concentrations indicate that deserts can be either small sources or sinks of N2O and that there may be significant consumption of arid soil N2O.

Contrasting effects of reindeer grazing on CO2, CH4, and N2O fluxes originating from the northern boreal forest floor

AbstractReindeer (Rangifer tarandus L.) is considered to be an important mammalian herbivore, strongly influencing Arctic lichen‐dominated ecosystems. There is no wide knowledge about the effect of reindeer on greenhouse gas (GHG) fluxes in northern boreal forests. Ground vegetation plays an important role in absorbing nitrogen (N) and carbon dioxide (CO2) from the atmosphere. Lately, it has also been found to be a significant source of nitrous oxide (N2O) and a small source of methane (CH4). We investigated the influence of reindeer grazing on field layer GHG (CO2, CH4, and N2O) fluxes, ground vegetation coverage and biomass, and soil physical properties (temperature and moisture) in a northern boreal forest. At our study site, the reindeer‐induced replacement of lichen by mosses had contrasting effects on the GHG fluxes originating from the field layer. Field layer CO2 efflux was significantly higher in grazed areas. The field layer was a CH4 sink in all areas, but grazed areas absorbed more CH4 compared to non‐grazed areas. Although total N2O fluxes remained around 0 in grazed areas, a small N2O sink occurred in non‐grazed areas with lower moss biomass. Our results indicated that grazing by reindeer in northern boreal forests affects GHG fluxes from the forest field layer both positively and negatively, and these emissions largely depend on grazing‐induced changes in vegetation composition.

High-Precision Measurement of N2O Concentration in Ice Cores.

Atmospheric nitrous oxide (N2O) is a greenhouse gas and ozone-depleting substance whose emissions are substantially perturbed by current human activities. Although air trapped in polar ice cores can provide direct information about N2O evolution, analytical precision was not previously sufficient for high temporal resolution studies. In this work, we present a highly improved analytical technique with which to study N2O concentrations in ancient-air-trapped ice cores. We adopt a melt-refreezing method to extract air and use a gas chromatography-electron capture detector (GC-ECD) to determine N2O concentrations. The GC conditions are optimized to improve the sensitivity for detecting N2O. Retrapped N2O in ice during the extraction procedure is precisely analyzed and corrected. We confirmed our results using data from the Styx Glacier ice core in Antarctica by comparing them with the results of a dry-extraction method. The precision estimated from the pooled standard deviation of replicated measurements of the Styx ice core was 1.5 ppb for ∼20 g of ice, a smaller sample of ice than was used in previous studies, showing a significant improvement in precision. Our preliminary results from the Styx Glacier ice core samples have the potential to define small N2O variations (a few parts per billion) at centennial time scales.

Soil responses to non-nitrogenous amendments in a nitrogen-saturated temperate forest: an unexpected decrease in methane oxidation after phosphorus and lime addition

We measured soil greenhouse gas fluxes and nutrient pools in a nitrogen (N)-polluted north-temperate forest and report relatively small N2O effluxes and high CH4 uptake. Six years after application, non-N fertilizers (P + K, lime) did not significantly reduce soil respiration or increase N2O efflux; however, rates of CH4 oxidation were significantly suppressed.

Long‐Term Grazing Alters Soil Trace Gas Fluxes from Grasslands in the Foothills of the Rocky Mountains, Canada

AbstractLong‐term cattle grazing may degrade grassland soils, but how soil CO2, CH4 and N2O fluxes respond to long‐term cattle grazing is poorly understood. Therefore, we quantified soil CO2, CH4 and N2O fluxes in response to four levels (none, light, heavy, very heavy) of long‐term (&gt;65 years) cattle grazing on a rough fescue grassland in the foothills of the Rocky Mountains, Canada over three grazing seasons. The grazed grassland soils emitted 37 to 51% more CO2 than non‐grazed soils. Grazed grassland soils were small CH4 sinks and small N2O sources each season, and their cumulative fluxes were significantly affected by a cattle stocking rate × year interaction, indicating the grazing effect was influenced by environmental conditions. Soil CH4 uptake was negatively correlated with soil moisture (r = −0·59). The 2013 grazing season had about 41% greater precipitation than average and grazing significantly decreased CH4 uptake 31 to 38% compared with non‐grazed soils. The N2O emissions were 122 to 179% greater with heavy and very heavy grazing than none in the wet season, unaffected by grazing in the normal precipitation season and 72% lower with light grazing than none in the dry season. Predicting trace gas fluxes from grazed grassland soils across space and time is difficult because of interactions among weather conditions, edaphic properties and grazing intensity. However, long‐term cattle grazing increased soil CO2 fluxes, while the grazing effect on CH4 uptake depended on precipitation and the soil N2O flux responded as a function of grazing intensity and precipitation. © 2016 Her Majesty the Queen in Right of Canada. Land Degradation &amp; Development Published by John Wiley &amp; Sons Ltd.

Transition Metal Complexes of Calix[4]arene: Theoretical Investigations into Small Guest Binding within the Host Cavity.

The ability to selectively detect or store small molecules, such as gases, is of enormous commercial potential. Calixarenes have been studied extensively as host molecules; however, recent synthetic advances have seen the formation of new polymetallic calixarene clusters, which have not yet been explored for such purposes. We therefore present a theoretical study, using Density Functional Theory, to thoroughly investigate the binding preferences of calix[4]arene, with a variety of transition metal cations coordinated to the calixarene tetraphenolic pocket, toward a series of important small molecules, H2S, SO2, H2O, O2, H2, N2, N2O, CO2, NH3, and HCN. It was found that the inclusion of a metal atom at the lower-rim of the calixarene caused significant strengthening of binding energy with all of the small molecules in our study as compared to metal-free calixarene. The guests, SO2 and NH3, were found to bind strongest with H2 binding weakest. Our calculations predict that simply introducing metal coordination of any type to calix[4]arene will make the largest difference to the binding energies. Subsequently changing the type, oxidation state, or the spin state of the metal coordinated to the calixarene tetraphenolic pocket was found to have a lesser effect on these.

Methane and nitrous oxide emissions due to excreta returns from grazing cattle in Nasu, Japan

AbstractTo quantify emissions of methane (CH4) and nitrous oxide (N2O) from the excreta returns of grazing cattle, we used a closed‐chamber method to quantify the fluxes of CH4 and N2O from patches of dung, urine and untreated grassland (control) within an experimental site. Fresh dung or urine of beef cattle was applied five times at different times of year to simulate excreta deposition from year‐round grazing. CH4 fluxes were greatest immediately after dung deposition and returned to control fluxes within 10–35 days. When precipitation occurred following dung deposition, CH4 fluxes temporarily increased. Once CH4 emission ceased, however, later rewetting did not lead to a resumption of CH4 emission. CH4 emission factors for dung (CH4 EFdung) averaged 0.052%. During the normal grazing period from May to October, the mean CH4 EFdung was estimated to be 0.076%. The CH4 fluxes were not significantly affected by urine deposition. However, N2O fluxes increased only slightly following dung deposition. During the grass‐growing period, N2O fluxes increased after urine deposition, reached a maximum within 3–14 days, and then returned to the levels measured from untreated controls within 28–35 days. During the winter, N2O fluxes increased slightly after urine deposition. However, relatively small N2O fluxes, typically less than 100 μg N m−2 h−1, were observed intermittently following rainfall events. The N2O emission factors for dung (N2O EFdung) averaged 0.013%, and those for urine (N2O EFurine) averaged 0.570%. During the normal grazing period from May to October, the mean N2O EFdung and N2O EFurine were estimated to be 0.024% and 0.684%, respectively. These results suggest that CH4 and N2O emissions from manure could be reduced by grazing cattle and leaving their manure in the field as opposed to housing cattle and composting their manure.

Intercomparison of fast response commercial gas analysers for nitrous oxide flux measurements under field conditions

Abstract. Four gas analysers capable of measuring nitrous oxide (N2O) concentration at a response time necessary for eddy covariance flux measurements were operated from spring until winter 2011 over a field cultivated with reed canary grass (RCG, Phalaris arundinacea, L.), a perennial bioenergy crop in eastern Finland. The instruments were TGA100A (Campbell Scientific Inc.), CW-TILDAS-CS (Aerodyne Research Inc.), N2O / CO-23d (Los Gatos Research Inc.) and QC-TILDAS-76-CS (Aerodyne Research Inc.). The period with high emissions, lasting for about 2 weeks after fertilization in late May, was characterized by an up to 2 orders of magnitude higher emission, whereas during the rest of the campaign the N2O fluxes were small, from 0.01 to 1 nmol m−2 s−1. Two instruments, CW-TILDAS-CS and N2O / CO-23d, determined the N2O exchange with minor systematic difference throughout the campaign, when operated simultaneously. TGA100A produced the cumulatively highest N2O estimates (with 29% higher values during the period when all instruments were operational). QC-TILDAS-76-CS obtained 36% lower fluxes than CW-TILDAS-CS during the first period, including the emission episode, whereas the correspondence with other instruments during the rest of the campaign was good. The reasons for systematic differences were not identified, suggesting further need for detailed evaluation of instrument performance under field conditions with emphasis on stability, calibration and any other factors that can systematically affect the accuracy of flux measurements. The instrument CW-TILDAS-CS was characterized by the lowest noise level (with a standard deviation of around 0.12 ppb at 10 Hz sampling rate) as compared to N2O / CO-23d and QC-TILDAS-76-CS (around 0.50 ppb) and TGA100A (around 2 ppb). We identified that for all instruments except CW-TILDAS-CS the random error due to instrumental noise was an important source of uncertainty at the 30 min averaging level and the total stochastic error was frequently of the same magnitude as the fluxes when N2O exchange was small at the measurement site. Both instruments based on continuous-wave quantum cascade laser, CW-TILDAS-CS and N2O / CO-23d, were able to determine the same sample of low N2O fluxes with a high mutual coefficient of determination at the 30 min averaging level and with minor systematic difference over the observation period of several months. This enables us to conclude that the new-generation instrumentation is capable of measuring small N2O exchange with high precision and accuracy at sites with low fluxes.

N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O, NO, N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emissions from tropical savanna and grassland of northern Australia: an incubation experiment with intact soil cores

Abstract. Strong seasonal variability of hygric and thermal soil conditions are a defining environmental feature in northern Australia. However, how such changes affect the soil–atmosphere exchange of nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2) is still not well explored. By incubating intact soil cores from four sites (three savanna, one pasture) under controlled soil temperatures (ST) and soil moisture (SM) we investigated the release of the trace gas fluxes of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to denitrification was measured using the helium gas flow soil core technique. Under dry pre-incubation conditions NO and N2O emissions were very low (&lt;7.0 ± 5.0 μg NO-N m−2 h−1; &lt;0.0 ± 1.4 μg N2O-N m−2 h−1) or in the case of N2O, even a net soil uptake was observed. Substantial NO (max: 306.5 μg N m−2 h−1) and relatively small N2O pulse emissions (max: 5.8 ± 5.0 μg N m−2 h−1) were recorded following soil wetting, but these pulses were short lived, lasting only up to 3 days. The total atmospheric loss of nitrogen was generally dominated by N2 emissions (82.4–99.3% of total N lost), although NO emissions contributed almost 43.2% to the total atmospheric nitrogen loss at 50% SM and 30 °C ST incubation settings (the contribution of N2 at these soil conditions was only 53.2%). N2O emissions were systematically higher for 3 of 12 sample locations, which indicates substantial spatial variability at site level, but on average soils acted as weak N2O sources or even sinks. By using a conservative upscale approach we estimate total annual emissions from savanna soils to average 0.12 kg N ha−1 yr−1 (N2O), 0.68 kg N ha−1 yr−1 (NO) and 6.65 kg N ha−1 yr−1 (N2). The analysis of long-term SM and ST records makes it clear that extreme soil saturation that can lead to high N2O and N2 emissions only occurs a few days per year and thus has little impact on the annual total. The potential contribution of nitrogen released due to pulse events compared to the total annual emissions was found to be of importance for NO emissions (contribution to total: 5–22%), but not for N2O emissions. Our results indicate that the total gaseous release of nitrogen from these soils is low and clearly dominated by loss in the form of inert nitrogen. Effects of seasonally varying soil temperature and moisture were detected, but were found to be low due to the small amounts of available nitrogen in the soils (total nitrogen &lt;0.1%).

High temporal frequency measurements of greenhouse gas emissions from soils

Abstract. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the most important anthropogenic greenhouse gases (GHGs). Variation in soil moisture can be very dynamic, and it is one of the dominant factors controlling the net exchange of these three GHGs. Although technologies for high-frequency, precise measurements of CO2 have been available for years, methods for measuring soil fluxes of CH4 and N2O at high temporal frequency have been hampered by lack of appropriate technology for in situ real-time measurements. A previously developed automated chamber system for measuring CO2 flux from soils was configured to run in line with a new quantum cascade laser (QCLAS) instrument that measures N2O and CH4. Here we present data from a forested wetland in Maine and an agricultural field in North Dakota, which provided examples of both net uptake and production for N2O and CH4. The objective was to provide a range of conditions in which to run the new system and to compare results to a traditional manual static-chamber method. The high-precision and more-than-10-times-lower minimum detectable flux of the QCLAS system, compared to the manual system, provided confidence in measurements of small N2O uptake in the forested wetland. At the agricultural field, the greatest difference between the automated and manual sampling systems came from the effect of the relatively infrequent manual sampling of the high spatial variation, or "hot spots", in GHG fluxes. Hot spots greatly influenced the seasonal estimates, particularly for N2O, over one 74-day alfalfa crop cycle. The high temporal frequency of the automated system clearly characterized the transient response of all three GHGs to precipitation and demonstrated a clear diel pattern related to temperature for GHGs. A combination of high-frequency automated and spatially distributed chambers would be ideal for characterizing hot spots and "hot moments" of GHG fluxes.

The detectability of nitrous oxide mitigation efficacy in intensively grazed pastures using a multiple-plot micrometeorological technique

Abstract. Methodologies are required to verify agricultural greenhouse gas mitigation at scales relevant to farm management. Micrometeorological techniques provide a viable approach for comparing fluxes between fields receiving mitigation treatments and control fields. However, they have rarely been applied to spatially verifying treatments aimed at mitigating nitrous oxide emission from intensively grazed pastoral systems. We deployed a micrometeorological system to compare N2O flux among several ~1.5 ha plots in intensively grazed dairy pasture. The sample collection and measurement system is referred to as the Field-Scale Nitrous Oxide Mitigation Assessment System (FS-NOMAS) and used a tuneable diode laser absorption spectrometer to measure N2O gradients to high precision at four locations along a 300 m transect. The utility of the FS-NOMAS to assess mitigation efficacy depends largely on its ability to resolve very small vertical N2O gradients. The performance of the FS-NOMAS was assessed in this respect in laboratory and field-based studies. The FS-NOMAS could reliably resolve gradients of 0.039 ppb between a height of 0.5 and 1.0 m. The gradient resolution achieved corresponded to the ability to detect an inter-plot N2O flux difference of 26 μg N2O–N m−2 h−1 under the most commonly encountered conditions of atmospheric mixing (quantified here by a turbulent transfer coefficient), but this ranged from 11 to 59 μg N2O–N m−2 h−1 as the transfer coefficient ranged between its 5th and 95th percentile. Assuming a likely value of 100 μg N2O–N m−2 h−1 for post-grazing N2O fluxes from intensively grazed New Zealand dairy pasture, the system described here would be capable of detecting a mitigation efficacy of 26% for a single (40 min) comparison. We demonstrate that the system has considerably greater sensitivity to treatment effects by measuring cumulative fluxes over extended periods.

Nitrous oxide cycling in the water column and sediments of the oxygen minimum zone, eastern subtropical North Pacific, Southern California, and Northern Mexico (23°N-34°N)

Identifying sources and sinks of N2O can illuminate N cycling processes in marine systems, particularly where changes in dissolved O2 can lead to changes in N cycling pathways (i.e., nitrification versus denitrification). We measured N2O and concentration and their stable isotope ratios (δ15N and δ18O) in the water column and sediments of the oxygen minimum zone in the nearshore eastern subtropical North Pacific (23°N–34°N). Atmospheric efflux of N2O ranged from 2.2 to 17.9 μmol m−2 d−1 or about 2–20 times higher than in oxygenated regions of the North Pacific. Surface waters were a source of 15N-depleted and 18O-enriched N2O to the atmosphere, indicating a bacterial, not archaeal, nitrification N2O source. Stable isotopes indicated that nitrification in both surface and intermediate waters (∼0–200 m) was the major source of N2O in this study area, with denitrification acting as a small N2O sink in strongly O2-depleted waters. Denitrification had a larger impact on observed patterns of N2O and concentrations and isotope ratios in the southern oxygen minimum zone. Sediments were generally neutral or a weak sink for N2O, with only one site (Soledad basin) showing a positive efflux of +3.5 ± 1.0 μmol N2O-N m−2 d−1. Sediment fluxes of N2O at all sites were several orders of magnitude smaller than fluxes of dinitrogen, nitrate, and ammonium measured in previous studies and did not appear to impact water column N2O concentrations. N2O was less than 0.1% of the N2 efflux from sedimentary denitrification.

Experimentally investigating efficiency of using the catalytic blocks in a small N2O gas-generators with resonant initiation system

Experimentally investigating efficiency of using the catalytic blocks in a small N2O gas-generators with resonant initiation system