An inventory of nitrous oxide emissions from agriculture in the UK using the IPCC methodology: emission estimate,uncertainty and sensitivity analysis

Nitrous oxide emission from UK agriculture was estimated, using the IPCC default values of all emission factors and parameters, to be 87 Gg N₂O–N in both 1990 and 1995. This estimate was shown, however, to have an overall uncertainty of 62%. The largest component of the emission (54%) was from the direct (soil) sector. Two of the three emission factors applied within the soil sector, EF1 (direct emission from soil) and EF3_PRP (emission from pasture range and paddock) were amongst the most influential on the total estimate, producing a ±31 and +11% to −17% change in emissions, respectively, when varied through the IPCC range from the default value. The indirect sector (from leached N and deposited ammonia) contributed 29% of the total emission, and had the largest uncertainty (126%). The factors determining the fraction of N leached (Frac_LEACH) and emissions from it (EF5), were the two most influential. These parameters are poorly specified and there is great potential to improve the emission estimate for this component. Use of mathematical models (NCYCLE and SUNDIAL) to predict Frac_LEACH suggested that the IPCC default value for this parameter may be too high for most situations in the UK.Comparison with other UK-derived inventories suggests that the IPCC methodology may overestimate emission. Although the IPCC approach includes additional components to the other inventories (most notably emission from indirect sources), estimates for the common components (i.e. fertiliser and animals), and emission factors used, are higher than those of other inventories. Whilst it is recognised that the IPCC approach is generalised in order to allow widespread applicability, sufficient data are available to specify at least two of the most influential parameters, i.e. EF1 and Frac_LEACH, more accurately, and so provide an improved estimate of nitrous oxide emissions from UK agriculture.     

Indirect nitrous oxide emission from a nitrogen saturated spruce forest and general accuracy of the IPCC methodology

The relevance of indirect N₂O emission is a controversial topic which is subject to much uncertainty. Only a small number of studies measure the indirect N₂O emission at the interface from soil to stream. In addition, the majority of studies undertaken only cover a short-term period (<1 year). Therefore, limited information is available regarding the influence of seasonal or event effects, nor is there much information as to whether indirect N₂O emissions are reflected by N₂O in soil solutions. The present study aimed at clarifying these two questions along with the general relevance of dissolved nitrous oxide. A wetness gradient involving soil solutions of different soil types and surface waters within an N-saturated forest catchment (3.2 ha) was monitored over a period of 1 year. N₂O concentrations in soil solutions (0.09–16.6 μg N l⁻¹) were affected by events such as dry–wet cycles but did not reflect to the actual, indirect N₂O emission at the soil-stream interface. It was assumed that N₂O emission was due to N transformation processes. The N₂O concentration at the spring was three times higher than the N₂O concentrations in the soil solutions. Nevertheless, indirect N₂O emission was still subordinate (<1%) to the direct emission of N₂O. The weekly amount of indirect N₂O emissions depended only on the stream flow rate (62% of the total annual amount). For this reason it was necessary to measure indirect N₂O emission at short intervals and at the interface between soil and stream over a longer time period. Our results and the results of the reviewed studies show that the default IPCC emission factor (EF5-g=1.5%) overestimates the indirect N₂O emission from ecosystems. The emission factor should therefore be lowered to about 0.1–0.3%. In addition, the results indicate that indirect N₂O emission is an insignificant pathway in the N cycle of most ecosystems. However, final judgement will depend on long-term studies.     

Developing spatially stratified N(2)O emission factors for Europe

We investigate the possibility to replace the – so-called – Tier 1 IPCC approach to estimate soil N₂O emissions with stratified emissions factors that take into account both N-input and the spatial variability of the environmental conditions within the countries of the European Union, using the DNDC-Europe model. Spatial variability in model simulations is high and corresponds to the variability reported in literature for field data. Our results indicate that (a) much of the observed variability in N₂O fluxes reflects the response of soils to external conditions, (b) it is likely that national inventories tend to overestimate the uncertainties in their estimated direct N₂O emissions from arable soils; (c) on average over Europe, the fertilizer-induced emissions (FIE) coincide with the IPCC factors, but they display large spatial variations. Therefore, at scales of individual countries or smaller, a stratified approach considering fertilizer type, soil characteristics and climatic parameters is preferable.     

A study on the evaluations of emission factors and uncertainty ranges for methane and nitrous oxide from combined-cycle power plant in Korea

In this research, in order to develop technology/country-specific emission factors of methane (CH₄) and nitrous oxide (N₂O), a total of 585 samples from eight gas-fired turbine combined cycle (GTCC) power plants were measured and analyzed. The research found that the emission factor for CH₄ stood at “0.82 kg/TJ”, which was an 18 % lower than the emission factor for liquefied natural gas (LNG) GTCC “1 kg/TJ” presented by Intergovernmental Panel on Climate Change (IPCC). The result was 8 % up when compared with the emission factor of Japan which stands at “0.75 kg/TJ”. The emission factor for N₂O was “0.65 kg/TJ”, which is significantly lower than “3 kg/TJ” of the emission factor for LNG GTCC presented by IPCC, but over six times higher than the default N₂O emission factor of LNG. The evaluation of uncertainty was conducted based on the estimated non-CO₂ emission factors, and the ranges of uncertainty for CH₄ and N₂O were between ?12.96 and +13.89 %, and ?11.43 and +12.86 %, respectively, which is significantly lower than uncertainties presented by IPCC. These differences proved that non-CO₂ emissions can change depending on combustion technologies; therefore, it is vital to establish country/technology-specific emission factors.     

Ammonia abatement and its impact on emissions of nitrous oxide and methane—Part 2: application for Europe

Agriculture is an important source of NH₃, which contributes to acidification and eutrophication, as well as emissions of the greenhouse gases CH₄ and N₂O. Because of their common sources, emission reduction measures for one of these gases may affect emissions of others. These interrelations are often ignored in policy making. This study presents an analysis of the effects of measures to reduce NH₃ emissions on emissions of N₂O and CH₄ from agriculture in Europe. The analysis combines information from the NH₃ module of the Regional Air pollution INformation and Simulation (RAINS) model for Europe with the IPCC method for national greenhouse gas inventories. The IPCC method for estimating agricultural emissions of N₂O and CH₄ is adjusted in order to use it in combination with the RAINS database for the European agricultural sector. As an example, we applied the adjusted method to the agricultural sector in the Netherlands and found that application of several NH₃ abatement options may result in a substantial increase in N₂O emissions while the effect on CH₄ emissions is relatively small. In Part 2 of this paper we focus on the resulting emissions for all European countries for 1990 and 2010.     

Ammonia abatement and its impact on emissions of nitrous oxide and methane in Europe—Part 1: method

Agriculture is an important source of NH₃, which contributes to acidification and eutrophication, as well as emissions of the greenhouse gases CH₄ and N₂O. Because of their common sources, emission reduction measures for one of these gases may affect emissions of others. These interrelations are often ignored in policy making. This study presents an analysis of the effects of measures to reduce NH₃ emissions on emissions of N₂O and CH₄ from agriculture in Europe. The analysis combines information from the NH₃ module of the Regional Air pollution INformation and Simulation (RAINS) model for Europe with the IPCC method for national greenhouse gas inventories. The IPCC method for estimating agricultural emissions of N₂O and CH₄ is adjusted in order to use it in combination with the RAINS database for the European agricultural sector. As an example, we applied the adjusted method to the agricultural sector in the Netherlands and found that application of several NH₃ abatement options may result in a substantial increase in N₂O emissions while the effect on CH₄ emissions is relatively small. In Part 2 of this paper we focus on the resulting emissions for all European countries for 1990 and 2010.     

Estimating and comparing greenhouse gas emissions with their uncertainties using different methods: A case study for an energy supply utility

Energy supply utilities release significant amounts of greenhouse gases (GHGs) into the atmosphere. It is essential to accurately estimate GHG emissions with their uncertainties, for reducing GHG emissions and mitigating climate change. GHG emissions can be calculated by an activity-based method (i.e., fuel consumption) and continuous emission measurement (CEM). In this study, GHG emissions such as CO₂, CH₄, and N₂O are estimated for a heat generation utility, which uses bituminous coal as fuel, by applying both the activity-based method and CEM. CO₂ emissions by the activity-based method are 12–19% less than that by the CEM, while N₂O and CH₄ emissions by the activity-based method are two orders of magnitude and 60% less than those by the CEM, respectively. Comparing GHG emissions (as CO₂ equivalent) from both methods, total GHG emissions by the activity-based methods are 12–27% lower than that by the CEM, as CO₂ and N₂O emissions are lower than those by the CEM. Results from uncertainty estimation show that uncertainties in the GHG emissions by the activity-based methods range from 3.4% to about 20%, from 67% to 900%, and from about 70% to about 200% for CO₂, N₂O, and CH₄, respectively, while uncertainties in the GHG emissions by the CEM range from 4% to 4.5%. For the activity-based methods, an uncertainty in the Intergovernmental Panel on Climate Change (IPCC) default net calorific value (NCV) is the major uncertainty contributor to CO₂ emissions, while an uncertainty in the IPCC default emission factor is the major uncertainty contributor to CH₄ and N₂O emissions. For the CEM, an uncertainty in volumetric flow measurement, especially for the distribution of the volumetric flow rate in a stack, is the major uncertainty contributor to all GHG emissions, while uncertainties in concentration measurements contribute a little to uncertainties in the GHG emissions.

Implications:Energy supply utilities contribute a significant portion of the global greenhouse gas (GHG) emissions. It is important to accurately estimate GHG emissions with their uncertainties for reducing GHG emissions and mitigating climate change. GHG emissions can be estimated by an activity-based method and by continuous emission measurement (CEM), yet little study has been done to calculate GHG emissions with uncertainty analysis. This study estimates GHG emissions and their uncertainties, and also identifies major uncertainty contributors for each method.     

Greenhouse gas emissions from dairy open lot and manure stockpile in northern China: A case study

The open lots and manure stockpiles of dairy farm are major sources of greenhouse gas (GHG) emissions in typical dairy cow housing and manure management system in China. GHG (CO₂, CH₄ and N₂O) emissions from the ground level of brick-paved open lots and uncovered manure stockpiles were estimated according to the field measurements of a typical dairy farm in Beijing by closed chambers in four consecutive seasons. Location variation and manure removal strategy impacts were assessed on GHG emissions from the open lots. Estimated CO₂, CH₄ and N₂O emissions from the ground level of the open lots were 137.5±64.7 kg hd^-1 yr^-1, 0.45±0.21 kg hd^-1 yr^-1 and 0.13±0.08 kg hd^-1 yr^-1, respectively. There were remarkable location variations of GHG emissions from different zones (cubicle zone vs. aisle zone) of the open lot. However, the emissions from the whole open lot were less affected by the locations. After manure removal, lower CH₄ but higher N₂O emitted from the open lot. Estimated CO₂, CH₄ and N₂O emissions from stockpile with a stacking height of 55±12 cm were 858.9±375.8 kg hd^-1 yr^-1, 8.5±5.4 kg hd^-1 yr^-1 and 2.3±1.1 kg hd^-1 yr^-1, respectively. In situ storage duration, which estimated by manure volatile solid contents (VS), would affect GHG emissions from stockpiles. Much higher N₂O was emitted from stockpiles in summer due to longer manure storage.

Implications: This study deals with greenhouse gas (GHG) emissions from open lots and stockpiles. It’s an increasing area of concern in some livestock producing countries. The Intergovernmental Panel on Climate Change (IPCC) methodology is commonly used for estimation of national GHG emission inventories. There is a shortage of on-farm information to evaluate the accuracy of these equations and default emission factors. This work provides valuable information for improving accounting practices within China or for similar manure management practice in other countries.     

Effect of biochar on nitrous oxide emission and its potential mechanisms

Extensive use of biochar to mitigate nitrous oxide (N₂O) emission is limited by the lack of understanding on the exact mechanisms altering N₂O emission from biochar-amended soil. Biochars produced from rice straw and dairy manure at 350 and 500 °C by oxygen-limited pyrolysis were used to investigate their influence on N₂O emission. A quadratic effect of biochar levels was observed on the N₂O emissions. The potential mechanisms were explored by terminal restriction fragment length polymorphism (T-RFLP) and real-time polymerase chain reaction (qPCR). A lower relative abundance of bacteria, which included ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), was observed at 4% biochar application rate. Reduced copy numbers of the ammonia monooxygenase gene amoA and the nitrite reductase gene nirS coincided with decreased N₂O emissions. Therefore, biochar may potentially alter N₂O emission by affecting ammonia-oxidizing and denitrification bacteria, which is determined by the application rate of biochar in soil.

Implications:Biochar research has received increased interest in recent years because of the potential beneficial effects of biochar on soil properties. Recent research shows that biochar can alter the rates of nitrogen cycling in soil systems by influencing nitrification and denitrification, which are key sources of the greenhouse gas nitrous oxide (N₂O). However, there are still some controversial data. The purpose of this research was to (1) examine how applications of different dose of biochar to soil affect emission of N₂O and (2) improve the understanding of the underlying mechanisms.     

城市污水污泥处置方式的温室气体排放比较分析

针对我国现在主流的城市污水污泥处置方法:填埋,焚烧,堆肥。用IPCC中推荐的方法和缺省值,对处置过程中产生的温室气体的直接排放、间接排放和替代排放做了计算和分析。填埋过程计算排放的温室气体有CH4,焚烧过程计算排放的有温室气体CO2和N2O,堆肥过程计算的排放的有温室气体CO2和N2O,最终比较的结果都折算成CO2的排放。结果表明,污泥填埋、焚烧、堆肥所产生的CO2的净排放量分别为695.847 kg CO2/t、443.643 kg CO2/t、511.817 kgCO2/t。由于考虑了堆肥以后的有机肥利用,从减排以及污泥资源化的角度分析,得出堆肥是相对好的污泥处置方式。     

Continuous Infrared Analysis of N2O in Combustion Products

Nitrous oxide (N₂O) levels in the atmosphere are increasing, potentially contributing to the greenhouse effect and depletion of stratospheric ozone. From a limited data base, combustion sources have been identified as a major anthropogenic source of N₂O. However, the existing data base (obtained by traditional grab sampling techniques followed by gas chromatographic analysis) is in question due to the discovery of a sampling artifact. A continuous on-line N₂O analyzer would enable and facilitate the accurate characterization of combustion sources over a range of operating conditions, and also aid in the development of an appropriate sampling technique. This paper addresses the development of a continuous measurement technique, and the evaluation and initial use of a field prototype continuous N₂O analyzer developed at the UCI Combustion Laboratory in cooperation with a major instrument manufacturer. The analyzer is capable of measuring N₂O levels down to a few ppm. The analyzer has been evaluated and used to study the N₂O emissions from a pulverized coal-fired boiler. The N₂O levels found with the analyzer are substantially lower than levels previously attributed to such sources. Initial N₂O measurements made with the analyzer suggest that N₂O levels are not a substantial fraction of the NO_X levels, as previously suggested.     

Testing DayCent and DNDC model simulations of N2O fluxes and assessing the impacts of climate change on the gas flux and biomass production from a humid pasture

Simulation models are one of the approaches used to investigate greenhouse gas emissions and potential effects of global warming on terrestrial ecosystems. DayCent which is the daily time-step version of the CENTURY biogeochemical model, and DNDC (the DeNitrification–DeComposition model) were tested against observed nitrous oxide flux data from a field experiment on cut and extensively grazed pasture located at the Teagasc Oak Park Research Centre, Co. Carlow, Ireland. The soil was classified as a free draining sandy clay loam soil with a pH of 7.3 and a mean organic carbon and nitrogen content at 0–20 cm of 38 and 4.4 g kg^?1 dry soil, respectively. The aims of this study were to validate DayCent and DNDC models for estimating N₂O emissions from fertilized humid pasture, and to investigate the impacts of future climate change on N₂O fluxes and biomass production. Measurements of N₂O flux were carried out from November 2003 to November 2004 using static chambers. Three climate scenarios, a baseline of measured climatic data from the weather station at Carlow, and high and low temperature sensitivity scenarios predicted by the Community Climate Change Consortium For Ireland (C4I) based on the Hadley Centre Global Climate Model (HadCM₃) and the Intergovernment Panel on Climate Change (IPCC) A1B emission scenario were investigated. DayCent predicted cumulative N₂O flux and biomass production under fertilized grass with relative deviations of +38% and (?23%) from the measured, respectively. However, DayCent performs poorly under the control plots, with flux relative deviation of (?57%) from the measured. Comparison between simulated and measured flux suggests that both DayCent model’s response to N fertilizer and simulated background flux need to be adjusted. DNDC overestimated the measured flux with relative deviations of +132 and +258% due to overestimation of the effects of SOC. DayCent, though requiring some calibration for Irish conditions, simulated N₂O fluxes more consistently than did DNDC. We used DayCent to estimate future fluxes of N₂O from this field. No significant differences were found between cumulative N₂O flux under climate change and baseline conditions. However, above-ground grass biomass was significantly increased from the baseline of 33 t ha^?1 to 45 (+34%) and 50 (+48%) t dry matter ha^?1 for the low and high temperature sensitivity scenario respectively. The increase in above-ground grass biomass was mainly due to the overall effects of high precipitation, temperature and CO₂ concentration. Our results indicate that because of high N demand by the vigorously growing grass, cumulative N₂O flux is not projected to increase significantly under climate change, unless more N is applied. This was observed for both the high and low temperature sensitivity scenarios.     

Calculation of σz and H for an Observed Vertical Profile of Concentration

ABSTRACT

In the present work, nitrous oxide emissions were estimated [mg/L] by the use of lysimeters under the closed chamber technique for a six month period. The lysimeters were classified by the type of irrigation used: one for drinking water, and the other for treated wastewater. Each lysimeter had two different types of soil (sand and clay), based on the types of soil in Chihuahua City, Mexico. An additional classification based on the depth was done (reticular and vadose zone). Each zone collected gas by the use of a closed chamber technique, allowing the samples to be taken for subsequent quantification and analysis by gas chromatography. A statistical analysis of variance (ANOVA) and principal components analysis (PCA) were conducted to identify the most influential variables or parameters in the formation of nitrous oxide. The variables that were considered for analysis were total Kjeldahl nitrogen (TKN), ammoniacal nitrogen (NH3-N), nitrate nitrogen (NO3-N), and nitrite nitrogen (NO2-N), along with meteorological parameters. In total, 58944 mg/L of N2O were emitted during the measurement period. The results showed that concentration emissions of N2O where the type of soil is sandy were smaller than those of clay soil, while the mean concentration in the vadose zone was higher than those in the reticular zone, regardless the type of soil. The parameters that showed greater influence in the N2O emissions were NO2-N and NO3-N concentrations. Temperature also played an important role in the emissions (the highest emissions were emitted during the cold months). Furthermore, denitrification appeared to be the dominant process in the production of nitrous oxide in soils.

Implications: Nitrous oxide (N₂O) emissions produced in lysimeters with two types of soil (sand and clay) at two different depths (vadose and reticular zones) using treated waste water showed that the higher emissions of N₂O are derived from clay soils in vadose zone; it could be due to the formation of clogging that favors the formation of anoxic conditions for the denitrification process. The parameters that showed more influence in the N₂O emissions were nitrite (NO₂-N) and nitrate (NO₃-N) concentrations along with the temperature.     

Seasonal and Spatial Variations of Ammonia Emissions from an Open-Lot Dairy Operation

Abstract

There is a need for a robust and accurate technique to measure ammonia (NH₃) emissions from animal feeding operations (AFOs) to obtain emission inventories and to develop abatement strategies. Two consecutive seasonal studies were conducted to measure NH₃ emissions from an open-lot dairy in central Texas in July and December of 2005. Data including NH₃ concentrations were collected and NH₃ emission fluxes (EFls), emission rates (ERs), and emission factors (EFs) were calculated for the open-lot dairy. A protocol using flux chambers (FCs) was used to determine these NH₃ emissions from the open-lot dairy. NH₃ concentration measurements were made using chemiluminescence-based analyzers. The ground-level area sources (GLAS) including open lots (cows on earthen corrals), separated solids, primary and secondary lagoons, and milking parlors were sampled to estimate NH₃ emissions. The seasonal NH₃ EFs were 11.6 ± 7.1 kg-NH₃ yr^-1head^-1 for the summer and 6.2 ± 3.7 kg-NH₃ yr^-1head^-1 for the winter season. The estimated annual NH₃ EF was 9.4 ± 5.7 kg-NH₃ yr^-1head^-1 for this open-lot dairy. The estimated NH₃ EF for winter was nearly 47% lower than summer EF. Primary and secondary lagoons (～37) and open-lot corrals (～63%) in summer, and open-lot corrals (～95%) in winter were the highest contributors to NH₃ emissions for the open-lot dairy. These EF estimates using the FC protocol and real-time analyzer were lower than many previously reported EFs estimated based on nitrogen mass balance and nitrogen content in manure. The difference between the overall emissions from each season was due to ambient temperature variations and loading rates of manure on GLAS. There was spatial variation of NH₃ emission from the open-lot earthen corrals due to variable animal density within feeding and shaded and dry divisions of the open lot. This spatial variability was attributed to dispirit manure loading within these areas.     

Field Measurements of Natural and Fertilizer-Induced N2O Release Rates from Soils

The influence of the soil on atmospheric N₂O was studied by In-situ measurements in 1976–1979 at several field stations near Mainz, Germany, where different soil types were located. Measurements were carried out using the closed chamber method and applying stainless steel capillaries allowing soil air sampling down to 60 cm depth. The N2O In soil was found to be produced and consumed simultaneously In the uppermost soil layer resulting In a net flux of N₂O with release rates of 0.5–16 μg N₂O–Nm^?2h^?1 on unfertilized natural as well as agriculturally used soils. After fertilization with mineral fertilizers the N₂O release rates increased to values ≤43 μg N₂O–Nm^?2h^?1. The total amount of fertilizer-N released Into the atmosphere as N₂O was determined to be 0.01–0.05% for nitrate and 0.03–0.09 % for ammonium fertilizer.     

Quantifying direct N2O emissions in paddy fields during rice growing season in mainland China: Dependence on water regime

Various water management regimes, such as continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding-moist intermittent irrigation, but without water logging (F-D-F-M), are currently practiced in paddy rice production in mainland China. These water regimes have incurred a sensitive change in direct N₂O emission from rice paddy fields. We compiled and statistically analyzed field data on N₂O emission from paddy fields during the rice growing season (71 measurements from 17 field studies) that were published in peer-reviewed Chinese and English journals. Seasonal total N₂O was, on average, equivalent to 0.02% of the nitrogen applied in the continuous flooding rice paddies. Under the water regime of F-D-F or the F-D-F-M, seasonal N₂O emissions increased with N fertilizer applied in rice paddies. An ordinary least square (OLS) linear regression model produced the emission factor (EF) of nitrogen for N₂O averaged 0.42%, but background N₂O emission was not pronounced under the water regime of F-D-F. Under the F-D-F-M water regime, N₂O EF and background emission were estimated to be 0.73% and 0.79 kg N₂O-N ha⁻¹, respectively, during the paddy rice growing season. Based on results of the present study and national rice production data, subsequently, direct N₂O emissions during the rice growing season amounted to 29.0 Gg N₂O-N with the uncertainty of 30.1%, which accounted for 7–11% of the reported estimates of annual total emission from croplands in mainland China. The results of this study suggest that paddy rice relative to upland crop production could have contributed to mitigating N₂O emissions from agriculture in mainland China.     

Development of a country-specific CO2 emission factor for domestic anthracite in Korea, 2007�C2009

Introduction

Korea has been making efforts to reduce greenhouse gas (GHG) emissions, including a voluntary commitment to the target of a 30% reduction, based on business-as-usual of the total GHG emission volume, by 2020; 2006 IPCC Guidelines provided default values, applying country-specific emission factors was recommended when estimating national greenhouse gas emissions.

Results and discussion

This study focused on anthracite produced in Korea in order to provide basic data for developing country-specific emission factor. This study has estimated CO₂ emission factors to use worksheet of which five steps consisted according to the fuel analysis method.

Conclusion

As a result, the average of net colorific value for 3 years (2007??2009) was 4,519 kcal/kg, and the CO₂ emission factor was calculated to be 111,446 kg/TJ, which is about 11.8% lower than the 2006 IPCC guidelines default value, and about 7.9% higher than the US EPA emission factor.     

A field trial of nutrient stimulation of methanotrophs to reduce greenhouse gas emissions from landfill cover soils

Landfills are among the major sources of anthropogenic methane (CH₄) estimated to reach 40?×?10⁹kg per year worldwide by 2015 (IPCC, 2007 IPCC. 2007. Intergovernmental Panel on Climate Change, Synthesis Report on Contributions of Work Groups 1, 2, and 3 to the Fourth Assessment Report Core Writing Team, Edited by: Pauchar, R.K. and Reisinger, A. Geneva, Switzerland: IPCC.  [Google Scholar]). A 2½-year field experiment was conducted at a closed landfill in western Michigan where methanotrophs, methane-consuming bacteria, were stimulated by nutrient addition to the soil without significantly increasing biogenic nitrous oxide (N₂O) production. The effects of the nitrogen amendments (KNO₃ and NH₄Cl), phenylacetylene (a selective inhibitor of nitrifying bacteria that contribute to N₂O production), and a canopy (to reduce direct water infiltration) on the vertical soil gas profiles of CH₄, CO₂, and O₂ were measured in the top meter of the soil. Methane and nitrous oxide fluxes were calculated from the corresponding soil gas concentration gradients with respect to depth and a Millington–Quirk diffusivity coefficient in soil derived empirically from soil porosity, water content, and diffusivity coefficients in air from the literature. Methane flux estimates were as high as 218.4 g m^?2 day^?1 in the fall and 12.8 g/m^?2 day^?1 in the summer. During the spring and summer, CH₄ fluxes were reduced by more than half by adding KNO₃ and NH₄Cl into the soil as compared to control plots, while N₂O fluxes increased substantially. The concurrent addition of phenylacetylene to the amendment decreased peak N₂O production by half and the rate of peak methane oxidation by about one-third. The seasonal average methane and N₂O flux data were extrapolated to estimate the reduction of CH₄ and N₂O fluxes into the atmosphere by nitrogen and inhibitor addition to the cover soils. The results suggest that such additions coupled with soil moisture management may provide a potential strategy to significantly reduce greenhouse gas emissions from landfills.

Implications The results of a 2½-year study of effects of nutrient stimulation on methane oxidation in landfill cover soils demonstrates that nutrient addition does decrease methane emissions. The work further underscores the control which soil moisture exerts on methane oxidation. Water management is critical to the success of methane oxidation strategies.     

Spatiotemporal variations of nitrous oxide (N2O) emissions from two reservoirs in SW China

Greenhouse gas emissions from hydroelectric dams have recently given rise to controversies about whether hydropower still provides clean energy. China has a large number of dams used for energy supply and irrigation, but few studies have been carried out on aquatic nitrous oxide (N₂O) variation and its emissions in Chinese river-reservoir systems. In this study, N₂O spatiotemporal variations were investigated monthly in two reservoirs along the Wujiang River, Southwest China, and the emission fluxes of N₂O were estimated. N₂O production in the reservoirs tended to be dominated by nitrification, according to the correlation between N₂O and other parameters. N₂O saturation in the surface water of the Wujiangdu reservoir ranged from 214% to 662%, with an average fluctuation of 388%, while in the Hongjiadu reservoir, it ranged from 201% to 484%, with an average fluctuation of 312%. The dissolved N₂O in both reservoirs was over-saturated with respect to atmospheric equilibrium levels, suggesting that the reservoirs were net sources of N₂O emissions to the atmosphere. The averaged N₂O emission flux in the Wujiangdu reservoir was 0.64 μmol m^?2 h^?1, while it was 0.45 μmol m^?2 h^?1 in the Hongjiadu reservoir, indicating that these two reservoirs had moderate N₂O emission fluxes as compared to other lakes in the world. Downstream water of the dams had quite high levels of N₂O saturation, and the estimated annual N₂O emissions from hydropower generation were 3.60 × 10⁵ and 2.15 × 10⁵ mol N₂O for the Wujiangdu and the Hongjiadu reservoir, respectively. These fluxes were similar to the total N₂O emissions from the reservoir surfaces, suggesting that water released from reservoirs would be another important way for N₂O to diffuse into the atmosphere. It can be concluded that dam construction significantly changes the water environment, especially in terms of nutrient status and physicochemical conditions, which have obvious influences on the N₂O spatiotemporal variations and emissions.     

Effects of land use conversion and fertilization on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O fluxes from typical hilly red soil

Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH₄) and nitrous oxide (N₂O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH₄ fluxes at the expense of increasing the N₂O fluxes. Furthermore, fertilization significantly decreased the CH₄ fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH₄ fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N₂O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH₄ emissions from the OF were 100 % lower, and N₂O emissions were 421 % higher than those from the PF. Although cumulative N₂O emissions were stimulated in the newly converted orchard, the strong reduction of CH₄ led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH₄ ⁺-N) and nitrate (NO₃ ^?-N) contents indicated a significant variation in soil properties and contributed to variations in soil CH₄ and N₂O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH₄ and N₂O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH₄ and N₂O emissions.