Indirect Nitrous Oxide Emissions Research Articles

Hydrologic Connectivity Regulates Riverine N2O Sources and Dynamics.

Indirect nitrous oxide (N2O) emissions from streams and rivers are a poorly constrained term in the global N2O budget. Current models of riverine N2O emissions place a strong focus on denitrification in groundwater and riverine environments as a dominant source of riverine N2O, but do not explicitly consider direct N2O input from terrestrial ecosystems. Here, we combine N2O isotope measurements and spatial stream network modeling to show that terrestrial-aquatic interactions, driven by changing hydrologic connectivity, control the sources and dynamics of riverine N2O in a mesoscale river network within the U.S. Corn Belt. We find that N2O produced from nitrification constituted a substantial fraction (i.e., >30%) of riverine N2O across the entire river network. The delivery of soil-produced N2O to streams was identified as a key mechanism for the high nitrification contribution and potentially accounted for more than 40% of the total riverine emission. This revealed large terrestrial N2O input implies an important climate-N2O feedback mechanism that may enhance riverine N2O emissions under a wetter and warmer climate. Inadequate representation of hydrologic connectivity in observations and modeling of riverine N2O emissions may result in significant underestimations.

Characterizing Spatial and Temporal Variations in N2O Emissions from Dairy Manure Management in China Based on IPCC Methodology

The emission factor method (Tier 1) recommended by the Intergovernmental Panel on Climate Change (IPCC) is commonly used to estimate greenhouse gas (GHG) emissions from livestock and poultry farms. However, the estimation accuracy may vary due to practical differences in manure management across China. The objectives of this study were to estimate the direct and indirect nitrous oxide (N2O) emissions from dairy manure management between 1990 and 2021 in China and characterize its spatial and temporal variations following IPCC guideline Tier 2. The N2O emission factor (EF) of dairy cow manure management systems was determined at the national level and regional level as well. The results showed that the national cumulative N2O emission of manure management from 1990 to 2021 was 113.1million tons of CO2 equivalent, ranging from 90.3 to 135.9 million tons with an uncertainty of ±20.2%. The annual EF was 0.021 kg N2O-N (kg N)−1 for total emissions, while it was 0.014 kg N2O-N (kg N)−1 for direct emissions. The proportions of N2O emissions in North China, Northeast China, East China, Central and Southern China, Southwest China and Northwest China were 32.3%, 18.6%, 11.4%, 5.8%, 6.1% and 25.8%, respectively. In addition, N2O emissions varied among farms in different scales. The respective proportions of total N2O emissions from small-scale and large-scale farms were 64.8% and 35.2% in the past three decades. With the improvement in farm management and milk production efficiency, the N2O emissions per unit mass of milk decreased from 0.77 × 10−3 kg to 0.48 × 10−3 kg in 1990–2021. This study may provide important insights into compiling a GHG emission inventory and developing GHG emission reduction strategies for the dairy farming system in China.

A fuzzy logic evaluation of synergies and trade-offs between agricultural production and climate change mitigation

This study introduces a trade-off evaluation system, the Σommit index, which considers four components: crop yield, soil carbon stock changes, direct and indirect nitrous oxide emissions, and nitrate-nitrogen leaching across alternative agronomic case scenarios, i.e., combinations of management practices within specific pedo-climatic conditions. The four trade-off components have been estimated by combining standard equations and emission factors from the Guidelines for National Greenhouse Gas Inventories, complemented with Grey Water Footprint accounting Guidelines and other meta-analyses. The Σommit index has been developed using a harmonised dataset of ∼1.8 million agronomic case scenarios, leveraging fuzzy logic to aggregate the trade-off components into a value ranging from 0 (bad) to 1 (good). It has been tested under three narratives reflecting stakeholders' sustainability priorities (young farmers, agrochemical companies, EU Common Agricultural Policy paying agency), using alternative weighting schemes derived from expert opinion. Adding organic matter input, intermediate N fertilisation (50–150 kg ha−1), no-tillage, winter cereal cultivation, and irrigation for summer cereals have consistently achieved higher performance across all narratives. When assigning a higher weight to soil carbon stock changes, a broader range of Σommit index values emerged, while assigning higher importance to crop yield has led to a narrower evaluation. We openly release the dataset of agronomic case scenarios, along with the scripts to replicate the methodology and an interactive dashboard to inspect the results. These resources are meant to be used by different stakeholders (e.g., policymakers, Common Agricultural Policy payment agencies, farms, agrochemical industry) as a complement to the Intergovernmental Panel on Climate Change methodology to improve current understanding and awareness of environmental trade-offs and synergies in agricultural management.

Aquaculture farm largely increase indirect nitrous oxide emission factors of lake

Freshwater aquaculture system is one of the main sources of nitrous oxide (N2O) and must be accounted for when reporting indirect N2O emissions from agricultural industries. The IPCC based approach recommend the indirect N2O emission factors (EF5) to estimate the emissions from freshwater. Unfortunately, the EF5 for lake aquaculture, one of the most common freshwater aquacultures, has never been reported due to the scarcity of field data. To better understand the magnitude of EF5 at lake aquaculture and identify the control factors, the EF5 at aquaculture farm and open water (non-aquaculture region) of Lake Taihu were investigated based on long-term (2012–2017) in-situ field measurements. Our results showed the indirect N2O emission at the aquaculture farm (1.52 ± 0.49 μmol m-2 d-1) was over one order of magnitude higher than at the open water (0.12 ± 0.49 μmol m-2 d-1). Furthermore, we also found large variability in the EF5, which varied by one order of magnitude across time. The EF5 was predicted by nitrogen and the mass ratio of carbon to nitrogen. The significantly higher mass ratio of DOC to DIN resulting from feed application contributed to substantial increase in the N2O production efficiency and EF5 at the aquaculture farm. The average EF5 at the aquaculture farm and open water were 0.0021 ± 0.0013 and 0.0013 ± 0.0010, respectively. However, the measured EF5 was lower than that IPCC’s default value of 0.0025, implying IPCC method yielded the overestimated indirect emission, and large bias will occur when only use constant value considering the dramatic variability of observed EF5.

Indirect nitrous oxide emission factors of fluvial networks can be predicted by dissolved organic carbon and nitrate from local to global scales.

Streams and rivers are important sources of nitrous oxide (N2 O), a powerful greenhouse gas. Estimating global riverine N2 O emissions is critical for the assessment of anthropogenic N2 O emission inventories. The indirect N2 O emission factor (EF5r ) model, one of the bottom-up approaches, adopts a fixed EF5r value to estimate riverine N2 O emissions based on IPCC methodology. However, the estimates have considerable uncertainty due to the large spatiotemporal variations in EF5r values. Factors regulating EF5r are poorly understood at the global scale. Here, we combine 4-year in situ observations across rivers of different land use types in China, with a global meta-analysis over six continents, to explore the spatiotemporal variations and controls on EF5r values. Our results show that the EF5r values in China and other regions with high N loads are lower than those for regions with lower N loads. Although the global mean EF5r value is comparable to the IPCC default value, the global EF5r values are highly skewed with large variations, indicating that adopting region-specific EF5r values rather than revising the fixed default value is more appropriate for the estimation of regional and global riverine N2 O emissions. The ratio of dissolved organic carbon to nitrate (DOC/NO3 - ) and NO3 - concentration are identified as the dominant predictors of region-specific EF5r values at both regional and global scales because stoichiometry and nutrients strictly regulate denitrification and N2 O production efficiency in rivers. A multiple linear regression model using DOC/NO3 - and NO3 - is proposed to predict region-specific EF5r values. The good fit of the model associated with easily obtained water quality variables allows its widespread application. This study fills a key knowledge gap in predicting region-specific EF5r values at the global scale and provides a pathway to estimate global riverine N2 O emissions more accurately based on IPCC methodology.

Estimation of carbon footprint and sources of emissions of an extensive alpaca production system.

A cradle-to-farm gate life cycle assessment was conducted following international standards (ISO 14040, 2006) to estimate sources of greenhouse gas emissions of an extensive alpaca production system in the Peruvian Andes with a focus on carbon footprint. The assessment encompasses all supply chain processes involved with the production of alpaca fiber and meat. Direct (i.e., enteric fermentation, manure, and manure management) and indirect emissions (i.e., electricity, fuel, and fertilizer) of carbon dioxide, nitrous oxide, and methane were estimated according to the (IPCC (Intergovernmental Panel on Climate Change). 2006. IPCC 2006 for National Greenhouse Gas Inventories. Volume 2, Chapter 3. Mobile Combustion. Volume 4, Chapter 10. Emissions from livestock and manure management. Chapter 11. N2O emissions from managed soils and CO2 emissions derived from the application of lime and urea. https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol4.html ). Carbon footprint was calculated based on a mass, economic, and biophysical allocation. The functional unit of the economic and mass allocations was 1kg of LW as the main product and 1kg of white or colored fiber as co-products. The functional unit of the biophysical allocation was 1kg of live weight and 1kg of fiber. The largest source of greenhouse gas emissions came from enteric fermentation (67%), followed by direct and indirect nitrous oxide emissions (29%). The estimated carbon footprint of the extensive alpaca production system, considering a 20% offtake rate, was 24.0 and 29.5kg of carbon dioxide equivalents per kg of live weight for the economic and mass allocations, respectively, while for the biophysical allocation was 22.6 and 53.0kg of carbon dioxide equivalents per kg of alpaca live weight and alpaca fiber, respectively. The carbon footprint per area was 88.6kg carbon dioxide equivalents per ha.

Distinctive Microbial Processes and Controlling Factors Related to Indirect N2O Emission from Agricultural and Urban Rivers in Taihu Watershed.

Inland rivers are hotspots of anthropogenic indirect nitrous oxide (N2O) emissions, but the underlying microbial processes remain poorly understood. This study measured N2O fluxes from agricultural and urban rivers in Taihu watershed and investigated the microbial processes driving N2O production and consumption. The N2O fluxes were significantly higher in agricultural rivers (140.1 ± 89.1 μmol m-2 d-1) than in urban rivers (25.1 ± 27.0 μmol m-2 d-1) (p < 0.001). All wind-based models significantly underestimated N2O flux in urban rivers (p < 0.05) when using the Intergovernmental Panel on Climate Change method because they underestimated the N2O emission factor (EF5r). Wind speed and nitrate were the key factors affecting N2O fluxes in agricultural and urban rivers, respectively. NirK-type denitrifiers produced N2O in urban river water, while nirS-type denitrifiers consumed N2O in the sediments of all rivers. Co-occurrence network analysis indicated organics from Microcystis served as electron donors for denitrifiers (dominated by Flavobacterium) in water, while direct interspecies electron transfer between Thiobacillus and methanogens and between Dechloromonas and sulfate-reducing bacteria enhanced N2O reduction in sediments. This study advances our knowledge on the distinctive microbial processes that determine N2O emissions in inland rivers and illustrates the need to revise EF5r for N2O estimation in urban rivers.

Spatial-temporal variability of indirect nitrous oxide emissions and emission factors from a subtropical river draining a rice paddy watershed in China

Indirect nitrous oxide (N2O) emissions from rivers draining agricultural watersheds are of increasing concerns due to riverine abundant sources of nitrogen loaded through leaching and runoff. However, the seasonal variation of N2O emissions from agricultural drainage rivers is poorly explored, especially the uncertainty in quantifying indirect N2O emission factors (EFs) from these aquatic environments. Here, a two-year study (2014-2016) was conducted to quantify indirect N2O emissions from a river draining a rice paddy watershed in subtropical China. Indirect N2O fluxes were simultaneously determined using the floating chamber method (chamber-based) and the gas exchange modeling approach (model-based) based on the measurement of dissolved N2O concentration. Results showed that seasonal dissolved N2O concentration and N2O fluxes had a similar variation pattern, with the highest and the lowest levels in summer and winter, respectively. The annual mean of model-based N2O fluxes (20.24 ± 3.34 μmol m−2 d−1) was generally in agreement with chamber-based N2O fluxes (18.70 ± 3.56 μmol m−2 d−1). The indirect emission factor of N2O was highly dependent on the surface water NO3−-N concentration. Annual mean indirect EF of N2O from the drainage river was estimated to be 0.00051, which was significantly lower than the default EF5r value (0.0025) proposed by the Intergovernmental Panel on Climate Change (IPCC). These results suggest that the use of IPCC default value might have overestimated indirect N2O emissions from agricultural impacted riverine systems. Our study also highlights that more extensive in-situ measurements are required for monitoring indirect N2O emissions from agricultural impacted waters with different drainage characteristics, which would benefit for refining the IPCC EF5r default value to further constrain global N2O budget.

Prioritize effluent quality, operational costs or global warming? – Using predictive control of wastewater aeration for flexible management of objectives in WRRFs

This study presents a general model predictive control (MPC) algorithm for optimizing wastewater aeration in Water Resource Recovery Facilities (WRRF) under different management objectives. The flexibility of the MPC is demonstrated by controlling a WRRF under four management objectives, aiming at minimizing: (A) effluent concentrations, (B) electricity consumption, (C) total operations costs (sum electricity costs and discharge effluent tax) or (D) global warming potential (direct and indirect nitrous oxide emissions, and indirect from electricity production) . The MPC is tested with data from the alternating WRRF in Nørre Snede (Denmark) and from the Danish electricity grid. Results showed how the four control objectives resulted in important differences in aeration patterns and in the concentration dynamics over a day. Controls B and C showed similarities when looking at total costs, while similarities in global warming potential for controls A and D suggest that improving effluent quality also reduced greenhouse gasses emissions. The MPC flexibility in handling different objectives is shown by using a combined objective function, optimizing both cost and greenhouse emissions. This shows the trade-off between the two objectives, enabling the calculation of marginal costs and thus allowing WRRF operators to carefully evaluate prioritization of management objectives. The long-term MPC performance is evaluated over 51 days covering seasonal and inter-weekly variations. On a daily basis, control A was 9–30% cheaper on average compared to controls A, D and to the current rule-based control. Similarly, control D resulted on average in 35–43% lower greenhouse gasses daily emission compared to the other controls. Difference between control performance increased for days with greater inter-diurnal variations in electricity price or greenhouse emissions from electricity production, i.e. when MPC has greater possibilities for exploiting input variations. The flexibility of the proposed MPC can easily accommodate for additional control objectives, allowing WRRF operators to quickly adapt the plant operation to new management objectives and to face new performance requirements.

Indirect nitrous oxide emissions from oilseed rape cropping systems by NH3 volatilization and nitrate leaching as affected by nitrogen source, N rate and site conditions

The aim of this study was to quantify site-specific levels of indirect nitrous oxide (N2O) emissions from oilseed rape (OSR) cropping in Germany, resulting from ammonia (NH3) volatilization after organic fertilizer application and nitrate (NO3−) leaching based on measurement in field experiments and additional simulation modelling. In field experiments in three years (2012/13–2014/15) at five sites representing the main OSR growing areas N fertilizer amount and type of fertilizer (mineral N or digestate (DIG)) were varied. NH3 emissions were measured after application of DIG with the Dräger Tube Method and dynamics of soil water and soil mineral nitrogen (SMN) were monitored for three years, besides other parameters influencing the N balance like plant growth. A Plant-Soil-Atmosphere-Model (PSAM) was developed from existing components to calculate site-specific N leaching. Furthermore, long term scenario analyses allowed to simulate site-specific N leaching and to analyze the impact of total N input and fertilizer N form on N uptake of OSR and the subsequent N leaching. Results showed site-specific differences in measured NH3 emissions after DIG application ranging from 7.6 to 18.3 % of total applied N representing a lower volatilization level than the IPCC default emission factor of 20 % for organic fertilizers. PSAM was able to reproduce observed dynamics of soil water and SMN, but with site-specific accuracy. N leaching levels varied site-specifically and were dependent on fertilizer amount, fertilizer type and site conditions (weather, soil), but ranged with 5.0–17.6% also considerably below the default value of 30 % N input used by IPCC. Finally, calculated N2O emissions resulting from measured NH3 volatilization was up to 61 % lower than the default value and N2O emissions from determined N leaching levels were 64–89% lower.

Calculation of the carbon footprint for family farms using the Farm Accountancy Data Network: A case from Lithuania

This study appraises the greenhouse gas (GHG) emissions for Lithuanian family farms based on the Intergovernmental Panel on Climate Change (IPCC) guidelines using Lithuanian emission factors from Lithuania’s National Inventory report (LNIR). Family farm activity data are derived from Lithuanian sample of the Farm Accountancy Data Network (FADN) for 2016. The GHG emission profile for Lithuanian family farms includes the estimates for methane (CH4) from enteric fermentation of domestic livestock population, CH4 from manure management, direct and indirect nitrous oxide (N2O) emissions from manure management, direct and indirect N2O emissions from managed soils, and carbon dioxide (CO2) from combustion of fuel. In Lithuanian family farms, on average, the key source categories of on-farms emissions were CH4 from enteric fermentation and N2O direct emissions from agricultural soils, as they together constituted 69.3% of the total emissions. The environmental pressures related to family farming were measured in terms of the Carbon Footprint (CF), which refers to the total amount of GHG produced by farming activities, and Carbon Intensity (CI) using a range of metrics including CI per land area, total output and Livestock Unit (LU). In 2016, CF stood at the average value of 57.8 t CO2eq farm−1, CI per UAA – 1.5 t CO2eq ha−1, CI per total output – 2.7 kg CO2eq EUR−1 and per LU – 6.0 t CO2eq LU−1.

Surface nitrous oxide (N2O) concentrations and fluxes from different rivers draining contrasting landscapes: Spatio-temporal variability, controls, and implications based on IPCC emission factor

Increasing indirect nitrous oxide (N2O) emission from river networks as a result of enhanced human activities on landscapes has become a global issue, as N2O has been widely recognized as an important ozone-depleting greenhouse gas. However, indirect N2O emissions from different rivers, particularly for those that drain completely different landscapes, are poorly understood. Here, we investigated the spatial-temporal variability of N2O emissions among the different rivers in the Chaohu Lake Basin of Eastern China. Our results showed that river reaches in urban watersheds are the hotspots of N2O production, with a mean N2O concentration of ∼410 nmol L−1, which is 9–18 times greater than those mainly draining forested (23 nmol L−1), agricultural (42 nmol L−1) and mixed (45 nmol L−1) landscapes. Riverine dissolved N2O was generally supersaturated with respect to the atmosphere. Such N2O saturation can best be explained by nitrogen availability, except for those in the forested watersheds, where dissolved oxygen is thought to be the primary predictor. The estimated N2O fluxes in urban rivers reached ∼471 μmol m−2 d−1, a value of ∼22, 13, and 11 times that in forested, agricultural and mixed watersheds, respectively. Averaged riverine N2O emission factors (EF5r) of the forested, agricultural, urban and mixed watersheds were 0.066%, 0.12%, 0.95% and 0.16%, respectively, showing different deviations from the default EF5r that released by IPCC in 2019. This points to a need for more field measurements with wider spatial coverage and finer frequency to further refine the EF5r and to better reveal the mechanisms behind indirect N2O emissions as influenced by watershed landscapes.

An estimation of greenhouse gas emission from livestock in Bangladesh.

Objectives:The study was undertaken to investigate the greenhouse gas (GHG) emission from livestock in Bangladesh.Materials and Methods:The GHG emission inventory of livestock in Bangladesh was estimated according to the tier 1 approach of the Intergovernmental Panel on Climate Change (IPCC) using livestock population data from 2005 to 2018. It was also extrapolated for the next three decades, according to the growth of the livestock population.Results:According to the calculation, the GHG emission from livestock was 66,586 Gg/year CO2 equivalent (CO2e) in 2018. This emission may rise to 69,869, 80,618, 94,638, and 113,098 Gg/year CO2e in 2020, 2030, 2040, and 2050, respectively. The share of enteric methane, manure methane, direct nitrous oxide emission, and indirect nitrous oxide emission in the total GHG emissions represented 44.0%, 3.6%, 51.5%, and 0.9%, respectively, in 2018. It may arise at a rate of 1.54%–1.74% annually until 2050.Conclusion:The GHG inventory may guide professionals to formulate and undertake the effective mitigation measures of GHG emissions from livestock in Bangladesh. However, this inventory can be amended following the tier 2 approach recommended by the IPCC if necessary data are available at the national level.

Characteristics of the Dissolved Nitrous Oxide (N2O) Concentrations and Influencing Factors in a Representative Agricultural Headwater Stream in the Upper Reach of the Yangtze River

Headwater streams around agricultural farmlands can act as important sinks of active nitrogen (N) and potential sources of indirect nitrous oxide (N2O) emissions, as well as aggravating agricultural non-point source N pollution. In this study, the dynamic characteristics of the dissolved N2O concentration in an agricultural headwater stream in the hilly area of purple soil in the upper reach of the Yangtze River were observed during the period Dec. 2014-Oct. 2015 by measuring the headspace gaseous N2O concentration using headspace equilibration-gas chromatography, and the dissolved N2O concentration was calculated according to the related parameters. Simultaneously, the physical and chemical parameters of the stream water were also monitored to understand the factors that affect the dissolved N2O concentration. The results showed that the dissolved N2O concentration in the agricultural headwater stream ranged from 0.26 to 1.28 μg·L-1 with an annual mean value of 0.57 μg·L-1, with nitrate (NO3--N, with an annual mean concentration of 1.45 mg·L-1) as the predominant reactive N form. The seasonal mean concentrations of the dissolved N2O in winter, spring, summer, and autumn were 0.63, 0.45, 0.53, and 0.64 μg·L-1, respectively, without significant seasonal variations. The annual dynamics of the dissolved N2O concentration were primarily governed by the concentration of NO3--N in the stream water, with denitrification being the main process producing N2O. The saturation levels of the dissolved N2O in the stream water showed oversaturation, with an annual mean value of 203.9% (109.7%-546.5%), with a seasonal pattern in which the saturation levels in the summer and autumn were higher than those in the winter and spring, indicating that the agricultural headwater stream can release indirect N2O emissions throughout the year. The temporal variations in the saturation levels of the dissolved N2O were mainly controlled by the water temperature and the NO3--N concentration of the stream water. During April-October, the concentration of dissolved N2O in the stream fluctuated obviously as a result of heavy rainfall, which resulted in an increase of the concentration of NO3-N in the stream water in the short term after the rain, which promoted denitrification and then increased the dissolved N2O level correspondingly.

Indirect Nitrous Oxide Emissions from an Agricultural Headwater Stream During the Rainy Season in the Upper Reach of the Yangtze River

Agricultural headwater streams have a close hydrologic connection with adjacent farmland ecosystems. Based on the aggravation of agricultural nonpoint source of nitrogen (N) pollution, these streams can become an important sink of N and source of indirect nitrous oxide (N2O) emission. In this study, indirect N2O emissions from an agricultural headwater stream in the hilly area of purple soil in the upper reach of the Yangtze River were measured in situ using the closed static chamber-GC technique during the rainy season (June to September 2015). The results show that the headwater stream is a source of indirect N2O emissions, with a mean emission rate of 12.8 μg·(m2·h)-1, which is close to the direct N2O emission level from local farmland during the same season. The indirect N2O emission factor (EF5r=0.01%) determined in this study is much lower than the default value proposed by the Intergovernmental Panel on Climate Change (0.25%; IPCC, 2006) for the estimation of indirect agricultural N2O emissions and far lower than the recalculated mean value (0.20%) based on available global data. However, based on the limited number of studies on EF5r and the high spatial variations among them, more in situ observations are needed and vital to generate more accurate EF5r values and reduce the uncertainty of indirect N2O estimations calculated based on the EF5r. The indirect N2O fluxes are positively correlated with the NO3--N concentrations of the stream. Thus, denitrification is the main process of N2O production. Moreover, the indirect N2O fluxes could be notably promoted by the rapid increase of the NO3--N concentrations that were driven by rainfall>9 mm during days with continuous rain.

Nitrous Oxide Fluxes from Agricultural Streams in East-Central Illinois

Indirect nitrous oxide (N2O) emissions account for the majority of uncertainty associated with the global N2O budget. Agricultural streams with subsurface (tile) drainage are potential hotspots of indirect N2O emissions from streams and groundwater. However, there are only a limited number of studies with direct measurements from stream surfaces. Research presented here represents the first study of N2O emissions from agricultural streams in Illinois, USA. We measured water chemistry data from 10 sites in three watersheds in east-central Illinois. Additionally, floating chambers and gas transfer velocity models were used to measure N2O fluxes from the stream surface at 4 of the 10 sites. Dissolved N2O concentrations ranged from < 0.1 to 7.46 μg N2O-N L−1. Floating chamber N2O fluxes ranged from 0 to 13.84 μg N2O-N m−2 min−1. We found strikingly different patterns of nitrate (NO3−) concentrations at sites downstream of a wastewater treatment plant (WWTP) effluent. Data from sites not affected by the WWTP expressed seasonal variations of NO3− with elevated concentrations in winter and spring months when subsurface tile drains were flowing. Floating chamber N2O fluxes were strongly correlated (p value 0.001) with NO3− at sites not affected by the WWTP. All sites were correlated with flow (p value 0.01) and dissolved N2O (p value 0.02). Our data suggest flow and dissolved N2O are stronger indicators of N2O flux from stream surfaces than NO3− concentrations in agricultural watersheds. Furthermore, this study supports growing concerns of estimating N2O emissions using linear relationships between N2O and NO3−, such as those used in IPCC estimates.

Simultaneous measurements of ammonia volatilisation and deposition at a beef feedlot

The nitrogen (N) excreted at intensive livestock operations is vulnerable to volatilisation, and, subsequently, may form a source of indirect nitrous oxide (N2O) emissions. The present study simultaneously investigated volatilisation and deposition of N at a beef feedlot, semi-continuously over a 129-day period. These data were examined relative to pen manure parameters, management statistics and emission-inventory calculation protocols. Volatilisation measurements were conducted using a single, heated air-sampling inlet, centrally located in a feedlot pen area, with real time concentration analysis via cavity ring-down spectroscopy and backward Lagrangian stochastic (bLS) modelling. Net deposited mineral-N was determined via two transects of soil-deposition traps, with samples collected and re-deployed every 2 weeks. Total volatilised ammonia amounted to 210 tonnes of NH3-N (127 g/animal.day), suggesting that the inventory volatilisation factor probably underestimated volatilisation in this case (inventory, 30% of excreted N; 65 g N volatilised/animal.day; a value of ~60% of excreted N is indicated). Temperature contrast between the manure and air was observed to play a significant role in the rate of emission (R2 = 0.38; 0.46 Kendall’s tau; P &amp;lt; 0.05). Net deposition within 600 m of the pen boundary represented only 1.7% to 3% of volatilised NH4+-N, between 3.6 and 6.7 tonnes N. Beyond this distance, deposition approached background rates (~0.4 kg N/ha.year).

Hydrogeological Controls on Regional-Scale Indirect Nitrous Oxide Emission Factors for Rivers.

Indirect nitrous oxide (N2O) emissions from rivers are currently derived using poorly constrained default IPCC emission factors (EF5r) which yield unreliable flux estimates. Here, we demonstrate how hydrogeological conditions can be used to develop more refined regional-scale EF5r estimates required for compiling accurate national greenhouse gas inventories. Focusing on three UK river catchments with contrasting bedrock and superficial geologies, N2O and nitrate (NO3-) concentrations were analyzed in 651 river water samples collected from 2011 to 2013. Unconfined Cretaceous Chalk bedrock regions yielded the highest median N2O-N concentration (3.0 μg L-1), EF5r (0.00036), and N2O-N flux (10.8 kg ha-1 a-1). Conversely, regions of bedrock confined by glacial deposits yielded significantly lower median N2O-N concentration (0.8 μg L-1), EF5r (0.00016), and N2O-N flux (2.6 kg ha-1 a-1), regardless of bedrock type. Bedrock permeability is an important control in regions where groundwater is unconfined, with a high N2O yield from high permeability chalk contrasting with significantly lower median N2O-N concentration (0.7 μg L-1), EF5r (0.00020), and N2O-N flux (2.0 kg ha-1 a-1) on lower permeability unconfined Jurassic mudstone. The evidence presented here demonstrates EF5r can be differentiated by hydrogeological conditions and thus provide a valuable proxy for generating improved regional-scale N2O emission estimates.

Determining the nitrous oxide transfer velocity and emission factor of an agricultural drain

ABSTRACTThere have been few studies examining indirect nitrous oxide emissions associated with nitrogen (N) leaching from agricultural soils. For agricultural drainage water, equals the water’s concentration in excess of the atmospheric value multiplied by the transfer velocity . Using this equation, tracers and chamber methods, and were measured from an agricultural drain. Estimates of were made by measuring water speed and depth using the relationship developed by O’Connor and Dobbins [1958. Mechanisms of reaeration in natural streams. Transactions of the American Society of Civil Engineers. 123:641–684]. The measurements and estimates were not significantly different and averaged 5 m d−1. Alternatively, for the method developed by the Intergovernmental Panel on Climate Change, equals the mass of N flowing in the water multiplied by an emission factor (EF). By additional measurements of the drain’s width, the water’s flow rate and nitrate () concentration, the estimated EF was 1.2 × 10−4 kg kg−1 .

Dissolved nitrous oxide (N2 O) dynamics in agricultural field drains and headwater streams in an intensive arable catchment

Indirect nitrous oxide (N2O) emissions produced by nitrogen (N) leaching into surface water and groundwater bodies are poorly understood in comparison to direct N2O emissions from soils. In this study, dissolved N2O concentrations were measured weekly in both lowland headwater streams and subsurface agricultural field drain discharges over a two-year period (2013–2015) in an intensive arable catchment, Norfolk, UK. All field drain and stream water samples were found to have dissolved N2O concentrations higher than the water–air equilibrium concentration, illustrating that all sites were acting as a net source of N2O emissions to the atmosphere. Soil texture was found to significantly influence field drain N2O dynamics, with mean concentrations from drains in clay loam soils (5.3 µg N L-1) being greater than drains in sandy loam soils (4.0 µg N L-1). Soil texture also impacted upon the relationships between field drain N2O concentrations and other water quality parameters (pH, flow rate, and nitrate (NO3) and nitrite (NO2) concentrations), highlighting possible differences in N2O production mechanisms in different soil types. Catchment antecedent moisture conditions influenced the storm event mobilisation of N2O in both field drains and streams, with the greatest concentration increases recorded during precipitation events preceded by prolonged wet conditions. N2O concentrations also varied seasonally, with the lowest mean concentrations typically occurring during the summer months (JJA). Nitrogen fertiliser application rates and different soil inversion regimes were found to have no effect on dissolved N2O concentrations, whereas higher N2O concentrations recorded in field drains under a winter cover crop compared to fallow fields revealed cover crops are an ineffective greenhouse gas emission mitigation strategy. Overall, this study highlights the complex interactions governing the dynamics of dissolved N2O concentrations in field drains and headwater streams in a lowland intensive agricultural catchment.