N2O Dynamics Research Articles

Residue incorporation depth is a controlling factor of earthworm‐induced nitrous oxide emissions

AbstractEarthworms can increase nitrous oxide (N2O) emissions, particularly in no‐tillage systems where earthworms are abundant. Here, we study the effect of residue incorporation depth on earthworm‐induced N2O emissions. We hypothesized that cumulative N2O emissions decrease with residue incorporation depth, because (i) increased water filled pore space (WFPS) in deeper soil layers leads to higher denitrification rates as well as more complete denitrification; and (ii) the longer upward diffusion path increases N2O reduction to N2. Two 84‐day laboratory mesocosm experiments were conducted. First, we manually incorporated maize (Zea mays L.) residue at different soil depths (incorporation experiment). Second, 13C‐enriched maize residue was applied to the soil surface and anecic species Lumbricus terrestris (L.) and epigeic species Lumbricus rubellus (Hoffmeister) were confined to different soil depths (earthworm experiment). Residue incorporation depth affected cumulative N2O emissions in both experiments (P < 0.001). In the incorporation experiment, N2O emissions decreased from 4.91 mg N2O–N kg−1 soil (surface application) to 2.71 mg N2O–N kg−1 soil (40–50 cm incorporation). In the earthworm experiment, N2O emissions from L. terrestris decreased from 3.87 mg N2O–N kg−1 soil (confined to 0–10 cm) to 2.01 mg N2O–N kg−1 soil (confined to 0–30 cm). Both experimental setups resulted in dissimilar WFPS profiles that affected N2O dynamics. We also found significant differences in residue C recovery in soil organic matter between L. terrestris (28–41%) and L. rubellus (56%). We conclude that (i) N2O emissions decrease with residue incorporation depth, although this effect was complicated by dissimilar WFPS profiles; and (ii) larger residue C incorporation by L. rubellus than L. terrestris indicates that earthworm species differ in their C stabilization potential. Our findings underline the importance of studying earthworm diversity in the context of greenhouse gas emissions from agro‐ecosystems.

Improving process-based estimates of N2O emissions from soil using temporally extensive chamber techniques and stable isotopes

Nitrous oxide (N2O) is an important greenhouse gas that is emitted from soil, but obtain- ing precise N2O source and sink strength estimates has been difficult due to high spatial and temporal flux variability and a poor understanding of the mechanisms controlling fluxes. Tools that improve our ability to quantify trace gas fluxes from soil and constrain annual budgets are therefore needed. Here we describe an improved chamber-based sampling system that continuously traps evolving soil gases onto molecular sieve thereby obtaining a single sample that integrates fluxes over extended periods (several weeks or more) and the use of stable isotopic methods to study microbial origins of N2O. We demonstrate that N2O can be trapped on molecular sieve within our chamber system with near 100% recovery and without isotopic fractionation. In field trials the site preference of N2O (the difference in d 15 N between the central and outer N atoms) varied between -6 and 14.4%, indicating that the majority of flux was derived from bacterial denitrification. Further development with automation would improve flux estimates by providing a system capable of capturing episodic flux events owing to long-term deployment. Further, an automated trapping chamber approach will also provide process-based understand- ing of N2O dynamics via stable isotopes and a new and affordable tool for evaluating the response of trace gas fluxes to land management practices.

A test of a field‐based 15N–nitrous oxide pool dilution technique to measure gross N2O production in soil

AbstractSoils are both a major source and sink of nitrous oxide (N2O), but the proportion of soil N2O production released to the atmosphere (termed the N2O yield) is poorly constrained due to the difficulty in measuring gross N2O production. The quantification of gross N2O fluxes would greatly improve our ability to predict N2O dynamics across the soil‐atmosphere interface. We report a new approach, the 15N2O pool dilution technique, to measure rates of gross N2O production and consumption under laboratory and field conditions. In the laboratory, gross N2O production and consumption compared well between the 15N2O pool dilution and acetylene inhibition methods whereas the 15NO3− tracer method measured significantly higher rates. In the field, N2O emissions were not significantly affected by increasing chamber headspace concentrations up to 100 ppb 15N2O. The pool dilution model estimates of 14N2O and 15N2O concentrations as well as net N2O fluxes fit observed data very well, suggesting that the technique yielded robust estimates of gross N2O production. Estimated gross N2O consumption rates were underestimated relative to rates calculated as the difference between gross and net N2O production rates, possibly due to heterogeneous and/or inadequate tracer diffusion to deeper layers in the soil profile. Gross N2O production rates were high, averaging 8.4 ± 3.2 mg N m−2 day−1, and were most strongly correlated to mineral nitrogen concentrations and denitrifying enzyme activity (R2 = 0.73). Gross N2O production rates varied spatially, with the highest rates in soils with the best drainage and the highest mineral N availability. Estimated and calculated N2O consumption rates constrained the average N2O yield from 0.70 to 0.84. Our results demonstrate that the 15N2O pool dilution technique can provide well‐constrained estimates of N2O yields and field rates of gross N2O production correlated to soil characteristics, improving our understanding of terrestrial N2O dynamics.

Hot spots for nitrous oxide emissions found in different types of permafrost peatlands

Recent findings on large nitrous oxide (N2O) emissions from permafrost peatlands have shown that tundra soils can support high N2O release, which is on the contrary to what was thought previously. However, field data on this topic have been very limited, and the spatial and temporal extent of the phenomenon has not been known. To address this question, we studied N2O dynamics in two types of subarctic permafrost peatlands, a peat plateau in Russia and three palsa mires in Finland, including also adjacent upland soils. The peatlands studied have surfaces that are uplifted by frost (palsas and peat plateaus) and partly unvegetated as a result of wind erosion and frost action. Unvegetated peat surfaces with high N2O emissions were found from all the studied peatlands. Very high N2O emissions were measured from peat circles at the Russian site (1.40±0.15 g N2O m−2 yr−1). Elevated, sparsely vegetated peat mounds at the same site had significantly lower N2O release. The N2O emissions from bare palsa surfaces in Northern Finland were highly variable but reached high rates, similar to those measured from the peat circles. All the vegetated soils studied had negligible N2O release. At the bare peat surfaces, the large N2O emissions were supported by the absence of plant N uptake, the low C : N ratio of the peat, the relatively high gross N mineralization rate and favourable moisture content, together increasing availability of mineral N for N2O production. We hypothesize that frost heave is crucial for high N2O emissions, since it lifts the peat above the water table, increasing oxygen availability and making it vulnerable to the the physical processes that may remove the vegetation cover. In the future, permafrost thawing may change the distribution of wet and dry surfaces in permafrost peatlands, which will affect N2O emissions.

Initial effects of forestry operations on N2O and vegetation dynamics in a boreal peatland buffer

Peatland buffer zones with sedimentation ponds are established with the intention of capturing solids and nutrients liberated in drained forestry catchments. As noted in earlier fertilization experiments, added nitrogen (N) immediately increases nitrous oxide (N2O) emissions in such buffers, and we expected the same to happen after disturbances in the catchment caused by clear-cutting, soil preparation, and ditch cleaning. We measured N2O fluxes, water table dynamics, and vegetation cover from a wetland one year before and two years after the clear-cut and buffer establishment. The low pre-harvest emissions did not increase, but N2O emissions from the sedimentation pond exceeded those from humic lakes with a high N load. In the soil profile, N2O concentrations were high, indicating a potential to produce N2O in the buffer. In one sub-site the soil N2O concentration was below the atmospheric level, which was in accordance with the high concentrations of carbon dioxide (CO2) and methane (CH4). The change in vegetation along the overland flow paths could be explained by a shift in the species thriving in wet conditions but not in those requiring higher nutrient levels. In spite of the apparent potential of soil to produce N2O, the fluxes to the atmosphere remained low. Transformation of N2O to unobserved N2 may explain some of the low N emissions, together with the low concentrations entering the buffer.

DOC and N2O dynamics in upland and peatland forest soils after clear-cutting and soil preparation

Forest clear-cutting followed by soil preparation means disturbance for soil microorganisms and disruption of N and C cycles. We measured fluxes of N2O and dissolved organic carbon (DOC) in upland soil (podzol) and adjacent peat within a clear-cut forest catchment. Both soil types behaved in a similar way, showing net uptake of N2O in the first year after the clear-cutting, and turning to net release in the second. The N2O flux dynamics were similar to those of N content in logging residues, as reported from a nearby site. As organic matter is used in the food web of the decomposers, we attempted to explain the dynamics of N2O uptake and release by measuring the concurrent dynamics of the low molecular weight (LMW) fraction and the aromaticity of DOC in a soil solution. The labile and most readily available LMW fractions of DOC were nearly absent in the year following the clear-cutting, but rose after two years. The more refractory high molecular weight (HMW) fraction of DOC decreased two years after the clear-cutting. The first year’s net uptake of N2O could be accounted for by the growth of decomposer biomass in the logging residues and detritus from the degenerating ground vegetation, resulting in immobilization of nitrogen. Simultaneously, the labile, LMW fraction of DOC became almost completely exhausted. The low availability of the LMW fraction could retard the growth and cause the accumulated decomposer biomass to collapse. During the following winter and summer the fraction of LMW clearly increased, followed by increased N2O emissions. The presence of LMW DOC fractions, not the concentration of DOC, seems to be an important controller for N2O liberation after a major disturbance such as clear-cutting and site preparation. The complex connection between DOC characteristics, nitrification or denitrification merits further studies.

Recovery of groundwater N2O at the soil surface and its contribution to total N2O emissions

Production and accumulation of the major greenhouse gas nitrous oxide (N2O) in surface groundwater might contribute to N2O emissions to the atmosphere. We report on a 15N tracer study conducted in the Fuhrberger Feld aquifer in northern Germany. A K15NO3 tracer solution (60 atom%) was applied to the surface groundwater on an 8 m2 measuring plot using 45 injection points in order to stimulate production of 15N2O by denitrification and to detect its contribution to emissions at the soil surface. Samples from the surface groundwater, from the unsaturated zone and at the soil surface were collected in regular intervals over a 72-days period. Total N2O fluxes at the soil surface were low and in a range between −7.6 and 29.1 μg N2O-N m−2 h−1. 15N enrichment of N2O decreased considerably upwards in the profile. In the surface groundwater, we found a 15N enrichment of N2O between 13 and 42 atom%. In contrast, 15N enrichment of N2O in flux chambers at the soil surface was very low, but a detectable 15N enrichment was found at all sampling events. Fluxes of groundwater-derived 15N-N2O were very low and ranged between 0.0002 and 0.0018 kg N2O-N ha−1 year−1, indicating that indirect N2O emissions from the surface groundwater of the Fuhrberger Feld aquifer occurring via upward diffusion are hardly significant. Due to these observations we concluded that N2O dynamics at the soil–atmosphere interface is predominantly governed by topsoil parameters. However, highest 15N enrichments of N2O throughout the profile were obtained in the course of a rapid drawdown of the groundwater table. We assume that such fluctuations may enhance diffusive N2O fluxes from the surface groundwater to the atmosphere for a short time.

N2O concentration and isotope signature along profiles provide deeper insight into the fate of N2O in soils†

Nitrous oxide is an important greenhouse gas and its origin and fate are thus of broad interest. Most studies on emissions of nitrous oxide from soils focused on fluxes between soil and atmosphere and hence represent an integration of physical and biological processes at different depths of a soil profile. Analysis of N2O concentration and isotope signature along soil profiles was suggested to improve the localisation of sources and sinks in soils as well as underlying processes and could therefore extend our knowledge on processes affecting surface N2O fluxes. Such a mechanistic understanding would be desirable to improve N2O mitigation strategies and global N2O budgets. To investigate N2O dynamics within soil profiles of two contrasting (semi)natural ecosystem types (a temperate acidic fen and a Norway spruce forest), soil gas samplers were constructed to meet the different requirements of a water-saturated and an unsaturated soil, respectively. The samplers were installed in three replicates and allowed soil gas sampling from six different soil depths. We analysed soil air for N2O concentration and isotope composition and calculated N2O net turnover using a mass balance approach and considering diffusive fluxes. At the fen site, N2O was mainly produced in 30–50 cm soil depth. Diffusion to adjacent layers above and below indicated N2O consumption. Values of δ15N and δ18O of N2O in the fen soil were always linearly correlated and their qualitative changes within the profile corresponded with the calculated turnover processes, suggesting further reduction of N2O. In the spruce forest, highest N2O production occurred in the topsoil, but there was also notable production occurring in the subsoil at a depth of 70 cm. Changes in N2O isotope composition as to be expected from local production and consumption processes within the soil profile did hardly occur, though. This was presumably caused by high diffusive fluxes and comparatively low net turnover, as isotope signatures approached values measured for ambient N2O towards the topsoil. Our results demonstrate a highly variable influence of diffusive versus production/consumption processes on N2O concentration and isotope composition, depending on the type of ecosystem. This finding indicates the necessity of further N2O concentration and isotope profile investigations in different types of natural and anthropogenic ecosystems in order to generalise our mechanistic understanding of N2O exchange between soil and atmosphere. Revised version of a paper presented at the 30th Annual Meeting of the German Association for Stable Isotope Research (GASIR), 8–10 October 2007, Bayreuth, Germany.

Nitrous oxide dynamics in managed northern forest soil profiles: is production offset by consumption?

This study investigates soil N2O dynamics in forest soils representing early (3-years) and late (>50 years) post-harvest succession in Atlantic Canada over a 9-month snow-free period in order to develop a better understanding of the role of managed forests as sources and sinks of N2O. We couple measurement of surface flux with detailed measurements of subsurface N2O concentrations at four mineral soil depths (0, 5, 20 and 35 cm) at 40 plots located within four sites. Median surface fluxes were similar at all sites regardless of the management stage (−5 to +19 ugN2O–N/m2/day), with all sites behaving as net sinks and sources of N2O over the measurement period. Subsurface mineral soil N2O concentrations at early (3-year) post-harvest succession sites, which ranged from median values of 362 ppbv at 0 cm to 1783 ppbv at 35 cm depth, were significantly higher than late post-harvest succession sites where median concentrations ranged from 329 ppbv at 0 cm to 460 ppbv at 35 cm depth. Examination of relationships between subsurface gas storage and surface flux magnitudes, suggested although recently harvested forest soils may be producing N2O at a greater rate than mature forest soils, observed patterns are consistent with a strong sink for this gas that prevents its conservative transport through the soil profile, and ultimate emission to the atmosphere through the majority of the measurement period.

The effect of different tillage and residue management practices on soil characteristics, inorganic N dynamics and emissions of N2O, CO2 and CH4 in the central highlands of Mexico: a laboratory study

Conservation agriculture in its version of permanent raised bed planting with crop residue retention increases yields and improves soil characteristics, e.g. aggregate distribution, organic matter content, so it remained to be seen how greenhouse gas emissions and dynamics of C and N might be altered. The objective of this study was to investigate how conservation agriculture with permanent raised beds, tied ridges, i.e. dykes within the furrows to prevent water run-off, and residue retention affected greenhouse gas emissions. A field experiment was started in 1999 comparing permanent and conventionally tilled raised beds with different residue management under rain fed conditions. Soil was characterized and emissions of CH4, N2O and CO2 and dynamics of NH4+, NO2− and NO3− were monitored in a laboratory experiment. The crop and tied ridges had no effect on soil characteristics and dynamics of C and N. Tilled beds reduced the water holding capacity (WHC) 1.1 times and increased conductivity 1.3 times compared to soil under nontilled beds with retention of all crop residues. The WHC, organic C, soil microbial biomass and total N were ≥1.1 larger in soil from nontilled beds where the crop residue was retained compared to where it was removed after only 6 years. The emission of CO2 was 1.2 times and production of NO3− 1.8 times larger in nontilled beds where the crop residue was retained compared to where it was removed. The CO2 emission was 1.2 times and the emission of N2O after 1 day 2.3 times larger in soil under tilled beds compared to nontilled beds with full residue retention, while the increase in concentration of NO3− was 0.05 mg N kg−1 soil in the former and 2.38 in the latter. We found that permanent raised bed planting with crop residue retention decreased emissions of N2O and CO2 compared to soil under conventionally tilled raised beds. Production of NO3− is larger in soil with permanent raised bed planting with crop residue retention compared to conventionally tilled raised beds.

Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity

Temperate pastures are often managed with P fertilizers and N2-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N2O) emissions and reduced methane (CH4) uptake. However, the diel and inter-daily variation in N2O and CH4 flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N2O and CH4 flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N2O and CH4 flux was measured continuously in a High P (23 kg P ha−1 yr−1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha−1 yr−1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH4 uptake was similar (−6.3 ± SE 0.3 to −8.6 ± 0.4 μg C m−2 hr−1) as were mean N2O emissions (6.5 to 7.9 ± 0.8 μg N m−2 hr−1), although N2O flux in the No P pasture did not respond to changing soil water conditions. N2O emissions were greatest in the Low P sheep camp (12.4 μg ± 1.1 N m−2 hr−1) where there were also net CH4 emissions of 5.2 ± 0.5 μg C m−2 hr−1. There were significant, but weak, relationships between soil water and N2O emissions, but not between soil water and CH4 flux. The diel temperature cycle strongly influenced CH4 and N2O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N2O emissions, or reduce CH4 uptake, during this 4 week measurement period, but the lack of an N2O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N2O and CH4 trace gas balance.

The dynamics of N2O near the groundwater table and the transfer of N2O into the unsaturated zone: A case study from a sandy aquifer in Germany

Abstract The research area was the Fuhrberger Feld aquifer (FFA) in northern Germany. It is situated about 30km northeast of the city of Hannover and covers about 300km2. Six multilevel sampling wells along a representative strip under predominantly arable land along a groundwater flow-line were sampled from the groundwater table down to a depth of 10m below the soil surface. We measured N2O, CO2, NO3−, SO42−, DOC, pH, redox potentials and O2 concentrations. N2O accumulated at four out of six wells close to the groundwater table. About 20% of N2O that occurred between the groundwater table and 7–8m below it resided in the top 0.4m. An exchange zone for N2O at the interface between the saturated and the unsaturated zone extended 0.55 ± 0.22m below the groundwater table and acted as a source and sink for N2O. N2O below the exchange zone cannot be transferred from the groundwater to the atmosphere. The upward fluxes from the exchange zone into the unsaturated zone at the six wells ranged between 0.0009 and 0.3kg N2O ha− 1 year− 1. The yearly downward fluxes into the exchange zones had about the same order of magnitude as the upward fluxes. The upward and downward fluxes of N2O at the (fluctuating) water table did cancel out each other, but this does not yet imply, that the N2O fluxes at the soil surface also cancel out each other. N2O–N:NO3–N ratios were highly variable ranging from 0.0002 to 0.0417. A multiple regression for the monthly N2O amounts in the exchange zone could explain 66% of the yearly variation. The significant variables were NO3−, CO2, pH, and O2. Therefore, a combination of the land use (NO3−), the geochemical boundary conditions (pH) and the type of denitrification reaction (O2 and CO2 indicate the importance of a heterotrophic denitrification process) governed the N2O dynamics in the surface groundwater of the FFA and its transfer into the unsaturated zone.

Relationship between major soil properties and culturable microorganisms affecting CH4 and N2O dynamics in rice soils

Microorganisms associated with methane (CH4) and nitrous oxide (N2O) dynamics were studied in eight rice (Oryza sativa L.) soils by culture-dependent most probable number (MPN) methods. Enumeration of methanogens showed that acetoclastic methanogens (104 to 109 cells g−1) outnumbered lithotrophic methanogens (103 cells g−1). Serological analysis indicated that type II methanotrophs belonging to Methylosinus and Methylocystis genera are probably the dominant CH4-oxidizing communities. For chemolithotrophic nitrifiers, nitrite oxidizers outnumbered ammonium oxidizers in most of the studied soils. The populations of both the acetoclastic methanogens (p = 0.05) and methanotrophs (p = 0.06) exponentially increased with the soil pH. Soil denitrifier populations (in a range of 103 to 106 cells g−1) exponentially decreased as soil C content increased (p = 0.03). Nitrifier and denitrifier populations generally showed a similar trend of variation with soil C/N ratio. The largest nitrifier populations were found in the Texas soil (C/N = 13.9), and largest denitrifier population in the Arkansas soil (C/N = 13.1). The relationships between the studied microbial groups and major soil properties help to understand the dynamics of CH4 and N2O production and consumption in soils.

Nitrous oxide emissions from agricultural land use in Germany— a synthesis of available annual field data

AbstractThe nations that have ratified the Kyoto Protocol must set up an appropriate national inventory on N2O emissions from agricultural land use, in order to report properly on the achievements made in reducing greenhouse‐gas emissions. The search for the appropriate method is a controversial topic as it is subject to high uncertainty in particular associated to the upscaling from site measurements. In this study, all available data from Germany on annual N2O‐emission rates derived from field experiments of at least an entire year are summarized. From each study, only differences in soil properties on N input qualified as an individual data set. Under these premises, 101 treatments from 27 sites were found equally spread across Germany. The annual N application ranged from 0 to 400 kg N ha–1 and the annual emission rates from 0.04 to 17.1 kg ha–1. Annual emission factors (EFs), uncorrected for background emission, varied considerably from 0.18% to 15.54% of N applied. There was no nationwide correlation found for the relationship between N2O losses and N application, soil C, soil N, soil texture, or soil pH. However, site‐specific trends in the relationship between emission factor and mean soil aeration status, as expressed by the soil type and/or mean climatic conditions, were revealed. Regularly water‐logged soils were characterized by low emission factors as were soils from the drier regions (<600 mm y–1), whereas well‐aerated soils from the frost‐intensive regions showed exceptionally high emission factors. Since purely physical and chemical parameterization failed to describe N2O emissions from agricultural land use on the national scale, there must be a biological adaptation to mean site conditions, i.e., different microbial communities react differently to similar actual conditions in terms of N2O dynamics. Regardless of the point of view, the chapter on N2O soil dynamics cannot be closed yet, and new additional model concepts, process studies, and field measurements are needed.

Atmosphere composition and N2O emissions in soils of contrasting textures fertilized with anhydrous ammonia

Nitrous oxide production and emission in agricultural soils are often influenced by soil physical properties and mineral N content. An experiment was initiated on a commercial farm located in the St. Lawrence Lowlands to measure the effects of recommended (150 kg N ha-1) and excessive (250 kg N ha-1) rates of anhydrous ammonia on atmospheric composition (O2, CO2, CH4 and N2O) and N2O emissions in soils of contrasting textures (sandy loam, clay loam and clay) cropped to corn. N2O emissions and soil temperature, water content and atmospheric composition were measured from post-harvest tillage to the first snowfall during the first year (2000), and from spring thaw to mid-July during the following 2 yr. Episodes of high N2O concentrations and surface emissions coincided with periods of high soil water content shortly following rainfall events when soil O2 concentrations were lowest. The convergence of indicators of restricted soil aeration at the time of highest N2O production suggested that denitrification was a major contributor to N2O emissions even in soils receiving an NH4-based fertilizer. Soil texture had a significant influence on soil N2O concentration and emission rates on several sampling dates. However, the effect was relatively small and it was not consistent, likely because of complex interactions between soil physical properties and N2O production, consumption and diffusion processes. Nitrous oxide emissions during the study were not limited by soil N availability as indicated by similar fluxes at recommended and excessive rates of anhydrous ammonia. Finally, greater N2O emissions in 2001 than in 2002 stress the importance of multiyear studies to evaluate the effect of annual weather conditions on soil N2O dynamics. Key words: Greenhouse gasses, denitrification

Elucidation of Biological N2O Emission Mechanisms and Its Significance in N2O Dynamics in a Waste Water Treatment Facility.

Tropospheric increment of N2O is of great concern in global warming issue and stratospheric ozone chemistry, which is largely attributed to the human-induced alteration of nitrogen cycle. Biological waste water treatment is a terminal destination of industrially fixed nitrogen as well as a hot spot for N2O emission. The present understanding of microbial pathways suggests that N2O is a by-product of ammonium oxidation and an obligate intermediate product of denitrification. Therefore, a conventional mass balance approach is insufficient to elucidate producing mechanisms of N2O in common environments where coupling of nitrification and denitrification occurs. In this context, we proposed the measurement of natural abundance of nitrogen and oxygen isotopes to be applied for analysis of N2O dynamics in a waste water treatment facility, and discussed future perspective of the technique.