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The anoxic/multi-aerobic process is widely applied for treating landfill leachate with low carbon to nitrogen ratio. In this study, the effect of two aeration modes in the aerobic phase, i.e. decreasing dissolved oxygen (DO) and increasing DO, on nitrogen removal and N 2 O emission in the process were systematically compared. The results demonstrate that the aerobic phase with increasing DO mode has a positive effect on improved total nitrogen removal (78 %) under the COD/N ratio as low as 3.45 and minimized N 2 O emission. DO concentration higher than 1.5 mg/L in the aerobic phase reduced nitrogen removal and led to a significant high N 2 O emission in the process. Complete nitrite denitrification in the anoxic phase correlated with minimized N 2 O emission. Under efficient nitrogen removal stage, N 2 O emission factor was 2.4 ± 1.0 % of the total incoming nitrogen. Microbial analysis revealed that increasing DO mode increased the abundance of ammonia oxidizing bacteria and denitrifiers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Nitrogen fertilisation contributes significantly to the atmospheric increase of nitrous oxide (N 2 O). Application of nitrification inhibitors (NIs) is a promising strategy to mitigate N 2 O emissions and improve N-use efficiency in agricultural systems. This study investigated the effect of NI, 3,4-dimethylpyrazol phosphate (DMPP) on N 2 O mitigation from spring barley and spring oilseed rape. Manual and automatic chamber methodologies were used to capture spatial and temporal variability in N 2 O emissions. In a second experiment, we study the effect of N fertiliser levels without NI (0 %, 50 %, 100 %, 150 % and 200 % of recommended amount of N fertiliser), as well as 100 % of N with NI on N 2 O emissions in spring barley. The automated chamber measurements showed dynamics of N 2 O changes throughout the season, including positive and negative peaks that were unobservable with manual chambers due to low temporal resolution. Although not significant, application of NI tended to reduce N 2 O emissions. The reduction was on average 16 % in spring barley and 58 % in spring oilseed rape in manual chamber measurements. However, N 2 O reduction was 108 % in continuous automatic chamber measurements in spring barley. The N 2 O EFs for the growing season were very low (0.025 % to 0.148 %), with a greater reduction in EF in spring oilseed rape (76 %) than in spring barley (32 %) with NI application. A positive correlation (R = 80 %) was observed between N fertiliser levels and N 2 O emissions. Crop yield and crop N uptake were not significantly affected by the use of NI. This study highlighted that NI can reduce N 2 O emissions, but the reduction effects are plot, crop and microclimate specific. Long-term experiments with continuous plot-scale measurements are needed to capture and optimise N 2 O mitigation effect of NIs across wide variability in soils and microclimates in agroecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

As a novel and sustainable technology, membrane-aerated biofilm reactors (MABR) performing simultaneous nitrification and denitrification face the challenge of undesirable nitrous oxide (N 2 O) emission. Thereby, a comprehensive analysis of N 2 O turnover pathways and the affecting parameters in MABR are demanded for N 2 O mitigation strategies. In this work, a mathematical model describing three N 2 O turnovers pathways was studied to uncover the underlying mechanisms and the impacts of operational conditions on N 2 O turnovers in MABR system performing simultaneous nitrification and denitrification. The modeling results demonstrate that higher oxygen surface loading, longer hydraulic retention time (HRT) and lower influent chemical oxygen demand (COD) significantly induce higher N 2 O production factor (0.18%-3.3%). N 2 O turnovers are mainly regulated by the hydroxylamine (NH 2 OH) pathway and heterotrophic bacteria (HB) denitrification, accounting for 76%-87% and 10%-21%, respectively. In contrast, the thicker biofilm (i.e., 400-600 μm) causes lower N 2 O production factor (<0.13%), due to the shift of N 2 O turnover pathways to the ammonium oxidizing bacteria (AOB) denitrification pathway (7.1%-9.3%) and HB denitrification (90.7%-92.9%). Meanwhile, the result of in-biofilm N 2 O conversion rates shows that the NH 2 OH pathway and HB denitrification become the predominant N 2 O production pathway at the inner zone (0-160 μm) and the outer zone (290-350 μm) of the biofilm in MABR, respectively. The biofilm thickness at 160-280 μm can thus be regarded as an optimal zone to reduce N 2 O production in MABR, due to more electrons preferentially used for N 2 O reduction. The relatively low N 2 O production factor (<0.5%) together with >80% total nitrogen (TN) removal in MABR can be achieved by controlling the oxygen surface loading (1.821-3.641 g/m 2 /d) and influent COD concentrations (285-500 mg/L) within a certain range., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Agricultural sustainability is compromised by nitrogen (N) losses caused by soil microbial activity. Nitrous oxide (N 2 O) is a potent greenhouse gas (GHG) produced as consequence of nitrification and denitrification processes in soils. Nitrification inhibitors (NI) as 3,4-dimethylpyrazole-succinic acid (DMPSA) are useful tools to reduce these N losses from fertilization. The objective of this work was to test the efficiency of DMPSA in two different tillage management systems, conventional tillage (CT) and no-tillage (NT), in a winter wheat crop under Humid Mediterranean conditions. N fertilizer was applied as ammonium sulphate (AS) with or without DMPSA in a single or split application, including an unfertilized treatment. GHG fluxes (N 2 O, CO 2 and CH 4 ) were measured by the closed chamber method. amoA and nosZI genes were quantified by qPCR as indicators of nitrifying and denitrifying populations. Nitrification was inhibited by DMPSA in both CT and NT, while the higher water filled pore space (WFPS) in NT promoted a better efficiency of DMPSA in this system. This higher efficiency might be due to a greater N 2 O reduction to N 2 as result of the nosZI gene induction. Consequently, DMPSA was able to reduce N 2 O emissions down to the unfertilized levels in NT. Provided that NT reduced CO 2 emissions and maintained crop yield compared to CT, the application DMPSA under NT management is a promising strategy to increase agro-systems sustainability under Humid Mediterranean conditions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 The Author(s). Published by Elsevier B.V. All rights reserved.)

A large amount of microplastics have entered conventional wastewater treatment plants, and their effects on activated sludge nitrification and denitrification are rarely reported. This study investigated the effects of microplastics on activated sludge nitrification and denitrification using five typical microplastics, namely, polyvinyl chloride (PVC), polypropylene, polyethylene, polystyrene, and polyester (PES) with concentrations of 0, 1000, 5000, and 10,000 particles/L. Results indicated that microplastics had negative effects on ammonia oxidation rate and low effect on nitrite oxidation rate during nitrification. The total inorganic nitrogen did not have much difference during 3 h nitrification under all the tested conditions. The addition of microplastics showed positive effects on denitrification, especially for PVC and PES at microplastic concentration of 5000 particles/L. Nitrification and denitrification did not evidently stop under all the tested conditions, indicating that the selected microplastic types and concentrations were not toxic to nitrification and denitrification within 3 h. The high abundance of PVC microplastics remarkably increased the nitrous oxide (N 2 O) emission during denitrification. The N 2 O emission in the test with 10,000 particle/L of PVC was 4.6times higher than the blank control. This study indicated that microplastics with <10,000 particle/L concentration in wastewater had low effects on nitrification and denitrification, whereas they had high effects on the N 2 O emission during denitrification., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Abstract Biochar can reduce both nitrous oxide (N 2 O) emissions and nitrate (NO 3 −) leaching, but refining biochar's use for estimating these types of losses remains elusive. For example, biochar properties such as ash content and labile organic compounds may induce transient effects that alter N-based losses. Thus, the aim of this meta-analysis was to assess interactions between biochar-induced effects on N 2 O emissions and NO 3 − retention, regarding the duration of experiments as well as soil and land use properties. Data were compiled from 88 peer-reviewed publications resulting in 608 observations up to May 2016 and corresponding response ratios were used to perform a random effects meta-analysis, testing biochar's impact on cumulative N 2 O emissions, soil NO 3 − concentrations and leaching in temperate, semi-arid, sub-tropical, and tropical climate. The overall N 2 O emissions reduction was 38%, but N 2 O emission reductions tended to be negligible after one year. Overall, soil NO 3 − concentrations remained unaffected while NO 3 − leaching was reduced by 13% with biochar; greater leaching reductions (>26%) occurred over longer experimental times (i.e. >30 days). Biochar had the strongest N 2 O-emission reducing effect in paddy soils (Anthrosols) and sandy soils (Arenosols). The use of biochar reduced both N 2 O emissions and NO 3 − leaching in arable farming and horticulture, but it did not affect these losses in grasslands and perennial crops. In conclusion, the time-dependent impact on N 2 O emissions and NO 3 − leaching is a crucial factor that needs to be considered in order to develop and test resilient and sustainable biochar-based N loss mitigation strategies. Our results provide a valuable starting point for future biochar-based N loss mitigation studies. Graphical abstract Unlabelled Image Highlights • N 2 O emissions were reduced by 38% with biochar. • Soil NO 3 − concentrations remained unaffected. • NO 3 − leaching was reduced by 13% with biochar. • Biochar strongly reduced N 2 O-emission in paddy and sandy soils. [ABSTRACT FROM AUTHOR]

Abstract Hydroxylamine (NH 2 OH) undergoes biotic and abiotic transformation processes in soil, producing nitrous oxide gas (N 2 O(g)). Little is known about the magnitude of the abiotic chemical processes in the global N cycle, and the role of abiotic nitrification is still neglected in most current nitrogen trace gas studies. The abiotic fate of NH 2 OH in soil systems is often focused on transition metals including manganese (Mn) and iron (Fe), and empirical correlations of nitrogen residual species including nitrite (NO 2 −), nitrate (NO 3 −), and N 2 O(g). In this study, abiotic NH 2 OH nitrification by well-characterized manganese (Mn)- and iron (Fe)-bearing minerals (pyrolusite, amorphous MnO 2 (s), goethite, amorphous FeOOH(s)) was investigated. A nitrogen mass balance analysis involving NH 2 OH, and the abiotic nitrification residuals, N 2 O(g), N 2 O(aq), NO 2 −, NO 3 −, was used, and specific reactions and mechanisms were investigated. Rapid and complete NH 2 OH nitrification occurred (4–5 h) in the presence of pyrolusite and amorphous MnO 2 (s), achieving a 95–96% mass balance of N byproducts. Conversely, NH 2 OH nitrification was considerably slower by amorphous FeOOH(s) (14.5%) and goethite (1.1%). Direct reactions between the Mn- and Fe-bearing mineral species and NO 2 − and NO 3 − were not detected. Brunauer–Emmett–Teller surface area and energy dispersive X-ray measurements for elemental composition were used to determine the specific concentrations of Mn and Fe. Despite similar specific concentrations of Mn and Fe in crystalline and amorphous minerals, the rate of NH 2 OH nitrification was much greater in the Mn-bearing minerals. Results underscore the intrinsically faster NH 2 OH nitrification by Mn minerals than Fe minerals. Graphical abstract Unlabelled Image Highlights • Abiotic NH 2 OH nitrification by Mn minerals was rapid, but not with Fe minerals. • The total N mass balance was: input = NH 2 OH; outputs = N 2 O(g) + N 2 O(aq) + NO 2 − + NO 3 −. • The total N recovery in 4.5 h using pyrolusite and amorph-MnO 2 (s) was 95–96%. • Total N recovery in 17 d using goethite and amorph-FeOOH(s) was 1.1–14.5%. • NH 2 OH nitrification by Mn was ≫Fe, despite similar specific [Mn] and [Fe] (mg/m2). [ABSTRACT FROM AUTHOR]

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) oxidize ammonia into nitrite, the first and rate-limiting step of microbial nitrification, and exert major controls over soil nitrogen transformations. The Loess Plateau in northwest China is characterized with deep soils that are often exposed to the surface and reactive nitrogen (N) inputs due to erosion and human removal of the surface soil. However, few have examined the distribution of AOA and AOB along the profile of Loess Plateau soils and their responses to N inputs. We examined the abundance and diversity of AOA and AOB along the soil profile (0–100 cm) and their responses to two levels of N inputs (low at 10, and high at 100 μg N g −1 soil) in a 55-d incubation experiment. While AOB were most numerous in the surface soil (0–20 cm), AOA were most abundant in the subsoils (20–40 and 40–60 cm), suggesting a niche differentiation between AOA and AOB along the soil profile. High N input increased AOB nearly ten-fold in the upper two layers of soils (0–20 and 20–40 cm) and sixteen to twenty-five fold in the deeper soil layers (40–60, 60–80 and 80–100 cm). However, it only increased AOA by 7% (40–60 cm) to 48% (20–40 cm). In addition, potential nitrification rate and N 2 O emissions correlated only with AOB. Finally, high N input significantly increased AOB diversity and led to nitrite accumulation in deep soil layers (60–80 and 80–100 cm). Together, our results showed that high N input can significantly alter the diversity and function of ammonia-oxidizing microbes in the deep soil of Loess Plateau, suggesting the need to examine the generality of the observed changes and their potential environmental impacts. [ABSTRACT FROM AUTHOR]

Bio-trenches are a sustainable option for treating nitrate contamination in groundwater. However, a possible side effect of this technology is the production of nitrous oxide, a greenhouse gas that can be found both dissolved in the liquid effluent as well as emitted as off gas. The aim of this study was to analyze NO 3 − removal and N 2 O production in lab-scale column trials. The column contained olive nut as organic carbon media. The experimental study was divided into three phases (I, II and III) each characterized by different inlet NO 3 − concentrations (30, 50, 75 mg NO 3 -N L −1 respectively). Sampling ports deployed along the length of the column allowed to observe the denitrification process as well as the formation and consumption of intermediate products, such as nitrite (NO 2 − ) and nitrous oxide (N 2 O). In particular, it was observed that N 2 O production represent only a small fraction of removed NO 3 − during Phase I and II, both for dissolved (0.007%) and emitted (0.003%) phase, and it was recorded a high denitrification efficiency, over 99%. Nevertheless, significantly higher values were recorded for Phase 3 concerning emitted phase (0.018%). This fact is due to increased inlet concentration which resulted in a carbon limitation and in a consequent decrease in denitrification efficiency (76%). [ABSTRACT FROM AUTHOR]

The development of intensive recirculating aquaculture systems (RAS) with low water exchange has accelerated in recent years as a result of environmental, economic and other concerns. In these systems, fish are commonly grown at high density, 50 to 150 kg/m 3 , using high-protein (30%–60%) feeds. Typically, the RAS consists of a solid treatment and a nitrification unit; in more advanced RAS, there is an additional denitrification step. Nitrous oxide (N 2 O), a byproduct during nitrification and denitrification processes, is a potent greenhouse gas that destroys the ozone layer. The aim of this study was to measure and assess N 2 O emissions from a near-zero discharge land-based saline RAS. N 2 O flux was monitored from the RAS's fish tank, and moving-bed nitrification and activated-sludge (with intrinsic C source) denitrification reactors. N 2 O emission potential was also analyzed in the laboratory. N 2 O flux from the denitrification reactors ranged between 6.5 and 48 mg/day, equivalent to 1.27 ± 1.01% of the removed nitrate-N. Direct analysis from the fish tank and nitrification reactors could not be performed due to high aeration, which diluted the N 2 O concentration to below detection limits. Thus, its potential emission was estimated in the laboratory: from the fishponds, it was negligible; from the nitrification reactor, it ranged between 0.4 and 2.8% of the total ammonia-N oxidized. The potential N 2 O emission from the denitrification reactor was 3.72 ± 2.75% of the reduced nitrate-N, within the range found in the direct measurement. Overall, N 2 O emission during N transformation in a RAS was evaluated to be 885 mg/kg feed or 1.36 g/kg fish production, accounting for 1.23% of total N application. Consequently, it is estimated that N 2 O emission from aquaculture currently accounts for 2.4% of the total agricultural N 2 O emission, but will decrease to 1.7% by 2030. [ABSTRACT FROM AUTHOR]

In suboxic or anoxic environments, nitrous oxide (N 2 O) can be produced by ammonia oxidizing bacteria (AOB) as a potent greenhouse gas. Although N 2 O producing inventory and pathways have been well-characterized using archetypal AOB, there is little known about their adaptive responses to oxic-anoxic cycling, which is a prevalent condition in soil, sediment, and wastewater treatment bioreactors. In this study, cellular responses of Nitrosomonas europaea 19718 to sustained anoxic-oxic cycling in a chemostat bioreactor were evaluated at transcriptomic, proteomic, and fluxomic levels. During a single oxic-anoxic transition, the accumulations of major intermediates were found at the beginning of anoxia (nitric oxide, NO) and post anoxia (hydroxylamine, NH 2 OH, and N 2 O). Anoxic-oxic cycling over thirteen days led to significantly reduced accumulations of NH 2 OH, NO and N 2 O. Distinct from short-term responses, which were mostly regulated at the mRNA level, adapted cells seemed to sustain energy generation under repeated anoxia by partially sacrificing the NO detoxification capacities, and such adaptation was mainly regulated at the protein level. The proteomic data also suggested the potential contributions of the newly discovered cytochrome P460-mediated NH 2 OH oxidation pathway to N 2 O productions. Flux balance analysis was performed based on a metabolic network model consisting of 49 biochemical reactions involved in nitrogen respiration, and changes in metabolic fluxes after the anoxic-oxic cycling were found to be better correlated with intracellular protein concentrations rather than mRNA levels. Previous studies focusing on single anoxic-oxic transition might have overlooked the adaptive responses of nitrifiers to anoxic-oxic cycling, and thus overestimated NO and N 2 O emission levels from natural and engineered nitrification systems. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors, a promising tool for reducing nitrous oxide (N 2 O) losses and promoting nitrogen use efficiency by slowing nitrification, have gained extensive attention worldwide. However, there have been few attempts to explore the broad responses of multiple reactive gaseous nitrogen emissions of N 2 O, nitric oxide (NO) and ammonia (NH 3 ) and vegetable yield to nitrification inhibitor applications across intensive vegetable soils in China. A greenhouse pot experiment with five consecutive vegetable crops was performed to assess the efficacies of two nitrification inhibitors, namely, nitrapyrin and dicyandiamide on reactive gaseous nitrogen emissions, vegetable yield and reactive gaseous nitrogen intensity in four typical vegetable soils representing the intensive vegetable cropping systems across mainland China: an Acrisol from Hunan Province, an Anthrosol from Shanxi Province, a Cambisol from Shandong Province and a Phaeozem from Heilongjiang Province. The results showed soil type had significant influences on reactive gaseous nitrogen intensity, with reactive gaseous nitrogen emissions and yield mainly driven by soil factors: pH, nitrate, C:N ratio, cation exchange capacity and microbial biomass carbon. The highest reactive gaseous nitrogen emissions and reactive gaseous nitrogen intensity were in Acrisol while the highest vegetable yield occurred in Phaeozem. Nitrification inhibitor applications decreased N 2 O and NO emissions by 1.8–61.0% and 0.8–79.5%, respectively, but promoted NH 3 volatilization by 3.2–44.6% across all soils. Furthermore, significant positive correlations were observed between inhibited N 2 O + NO and stimulated NH 3 emissions with nitrification inhibitor additions across all soils, indicating that reduced nitrification posed the threat of NH 3 losses. Additionally, reactive gaseous nitrogen intensity was significantly reduced in the Anthrosol and Cambisol due to the reduced reactive gaseous nitrogen emissions and increased yield, respectively. Our findings highlight the benefits of nitrification inhibitors for integrating environment and agronomy in intensive vegetable ecosystems in China. [ABSTRACT FROM AUTHOR]

Two greenhouse gases –methane (CH 4 ) and nitrous oxide (N 2 O) - were monitored monthly during one year (2011) at the Eguzon Reservoir in France. The objective of the study was to quantify for the first time in a temperate area the total emissions of these gases through the main emission pathways (diffusion and bubbling from the reservoir, degassing and downstream diffusion). The reservoir was impounded in 1926 and had, in 2011, a eutrophic status promoting high organic matter degradation and nitrification-denitrification, all favouring CH 4 and N 2 O production. CH 4 and N 2 O emissions were dominated by diffusion from the reservoir surface (respectively 78.0% and 92.3%). Ebullition was only observed for CH 4 and accounted for 14.0% of total CH 4 emissions. Downstream degassing and diffusion represented 8.1% of the total CH 4 emissions and 7.7% of the total N 2 O emissions. [ABSTRACT FROM AUTHOR]

Distribution of N 2 O has been determined in eight cruises along three transects (Guadalquivir, Sancti Petri and Trafalgar) in the Gulf of Cadiz, during 2014 and 2015. The mean N 2 O value for this area was 10.0 ± 0.9 nM, with large spatial and temporal variations. Stratification in the water column has been observed; the concentration of this gas increases with the depth, because of the presence of the Eastern North Atlantic Central Water (ENACW) and the Mediterranean Outflow Waters (MOW). The N 2 O production measured in this study is mainly due to nitrification. N 2 O yields from nitrification were estimated from the linear correlation of the excess of N 2 O (ΔN 2 O) with Apparent Oxygen Utilization (AOU) and nitrate (NO 3 − ), with values of their slopes ranged between 0.010 and 0.021% and 0.017–0.025% respectively. There is an onshore – offshore gradient of N 2 O; the highest values were found at the shallower stations, indicating coastal input and benthic remineralization. The seawater-air flux of N 2 O is affected by several variables (temperature, AOU and NO 3 − ), and the average flux calculated is 2.7 ± 2.0 μmol m − 2 d − 1 . The fluxes show a decrease with increasing distance from the coast, and with proximity to the Strait of Gibraltar. The study area behaves as a source of N 2 O to the atmosphere, with a global emission of 0.18 Gg year − 1 . [ABSTRACT FROM AUTHOR]

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N 2 O) in groundwater. N 2 O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance. The major anthropogenic source that contributes to N 2 O generation in aquifers is agriculture because the use of fertilizers has led to the widespread groundwater contamination by inorganic nitrogen (N) (mainly nitrate, NO 3 − ). Once in the aquifer, this inorganic N is transported and affected by several geochemical processes that produce and consume N 2 O. An inventory of dissolved N 2 O concentrations is presented and the highest concentration is about 18.000 times higher than air-equilibrated water (up to 4004 μg N L −1 ). The accumulation of N 2 O in groundwater is mainly due to denitrification and to lesser extent to nitrification. Their occurrence depend on the geochemical (e.g., NO 3 − , dissolved oxygen, ammonium and dissolved organic carbon) as well as hydrogeological parameters (e.g., groundwater table fluctuations and aquifer permeability). The coupled understanding of both parameters is necessary to gain insight on the dynamics and the emissions of N 2 O in groundwater. Overall, groundwater indirect N 2 O emissions seem to be a minor component of N 2 O emissions to the atmosphere. Further research might be devoted to evaluate the groundwater contribution to the indirect emissions of N 2 O because this will help to better constraint the N 2 O global budget and, consequently, the N budget. [ABSTRACT FROM AUTHOR]

N 2 O and NO emissions, the water usage and grain yields of a maize field in the North China Plain (NCP) under traditional flood irrigation, drip irrigation and drip fertigation were compared. With respect to the flood irrigation treatment, N 2 O emissions were reduced by 13.8% in the drip irrigation treatment and 7.7% in the drip fertigation treatment. NO emissions were reduced to 16.7% in the drip irrigation treatment but increased by 21.7% in the drip fertigation treatment. The molar ratios of NO/N 2 O within 2 days after each fertilization event were evidently greater from the drip fertigation treatment than from the flood irrigation treatment, indicating that nitrification was more intensive in the drip fertigation treatment than in the treatment of flood irrigation. Compared with the flood irrigation treatment, evident increase of the maize yields in the drip irrigation treatment (28%) and the drip fertigation treatment (3.7%) were found. Although the drip fertigation treatment could evidently increase NO emission, the 40% water reduction in drip fertigation is of great importance for the sustainable development of agriculture in the NCP where water resources are extremely limited. To mitigate NO emissions from agricultural fields in the NCP with drip fertigation, the addition of a nitrification inhibitor combined with N or nitrate fertilizer was recommended. [ABSTRACT FROM AUTHOR]

Agricultural soil has been recognized as a major source of atmospheric NO and N 2 O emissions which have important impacts on regional and global environments. Here we comparably investigated the effects of ammonium, nitrate fertilizers and nitrification inhibitor dicyandiamide (DCD) addition on NO and N 2 O emissions from the agricultural soil in the North China Plain (NCP). Compared with the ammonium fertilizer application, the reductions of NO emissions caused by nitrate fertilizer and DCD addition were 100% and 93%, and of N 2 O emissions were 54% and 74%, respectively. Remarkable reductions of NO and N 2 O emissions were also observed from five different agricultural soils in the NCP by replacing ammonium with nitrate fertilizer, indicating that nitrification is the predominant process for the emissions of NO and N 2 O from the soils in the vast area of NCP. NO emission peaks were found to be several days later than N 2 O peaks after the application of ammonium fertilizer and flooding irrigation, implying that most of NO initially produced via nitrification process might be fast reduced to N 2 O under the high soil moisture condition. Interestingly, the relative contribution of denitrification to N 2 O emission showed obviously time-dependent, e.g., evident N 2 O emission caused by the application of nitrate was only observed after the basal fertilization for the maize and the topdressing for the wheat. Replacing ammonium with nitrate fertilizer and mixing with the nitrification inhibitor are verified to be effective measures for mitigating NO and N 2 O emissions from arable soils in the NCP. [ABSTRACT FROM AUTHOR]

Nitrous oxide, carbon dioxide and methane are greenhouse gases (GHG) emitted from wastewater treatment that contribute to its carbon footprint. As a result of the increasing awareness of GHG emissions from wastewater treatment plants (WWTPs), new modelling, design, and operational tools have been developed to address and reduce GHG emissions at the plant-wide scale and beyond. This paper reviews the state-of-the-art and the recently developed tools used to understand and manage GHG emissions from WWTPs, and discusses open problems and research gaps. The literature review reveals that knowledge on the processes related to N 2 O formation, especially due to autotrophic biomass, is still incomplete. The literature review shows also that a plant-wide modelling approach that includes GHG is the best option for the understanding how to reduce the carbon footprint of WWTPs. Indeed, several studies have confirmed that a wide vision of the WWPTs has to be considered in order to make them more sustainable as possible. Mechanistic dynamic models were demonstrated as the most comprehensive and reliable tools for GHG assessment. Very few plant-wide GHG modelling studies have been applied to real WWTPs due to the huge difficulties related to data availability and the model complexity. For further improvement in GHG plant-wide modelling and to favour its use at large real scale, knowledge of the mechanisms involved in GHG formation and release, and data acquisition must be enhanced. [ABSTRACT FROM AUTHOR]

This study examines the effects of temperature on nitrous oxide (N 2 O) emissions in a bench-scale intensive aquaculture system rearing Koi fish. The water temperature varied from 15 to 24 °C at interval of 3 °C. Both volumetric and specific rate for nitrification and denitrification declined as the temperature decreased. The concentrations of ammonia and nitrite, however, were lower than the inhibitory level for Koi fish regardless of temperature. The effects of temperature on N 2 O emissions were significant, with the emission rate and emission factor increasing from 1.11 to 1.82 mg N 2 O-N/d and 0.49 to 0.94 mg N 2 O-N/kg fish as the temperature decreased from 24 to 15 °C. A global map of N 2 O emission from aquaculture was established by using the N 2 O emission factor depending on temperature. This study demonstrates that N 2 O emission from aquaculture is strongly dependent on regional water temperatures as well as on fish production. [ABSTRACT FROM AUTHOR]

Abstract: Ammonia oxidizers, including ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) are important drivers of a key step of the nitrogen cycle — nitrification, which affects the production of the potent greenhouse gas, nitrous oxide (N2O). A field experiment was conducted to determine the effect of nitrogen application rates and the nitrification inhibitor dicyandiamide (DCD) on the abundance of AOB and AOA and on N2O emissions in a grazed pasture soil. Nitrogen (N) was applied at four different rates, with urea applied at 50 and 100kgNha−1 and animal urine at 300 and 600kgNha−1. DCD was applied to some of the N treatments at 10kgha−1. The results showed that the AOB amoA gene copy numbers were greater than those of AOA. The highest ratio of the AOB to AOA amoA gene copy numbers was 106.6 which occurred in the urine-N 600 treatment. The AOB amoA gene copy numbers increased with increasing nitrogen application rates. DCD had a significant impact in reducing the AOB amoA gene copy numbers especially in the high nitrogen application rates. N2O emissions increased with the N application rates. DCD had the most significant effect in reducing the daily and total N2O emissions in the highest nitrogen application rate. The greatest reduction of total N2O emissions by DCD was 69% in the urine-N 600 treatment. The reduction in the N2O emission factor by DCD ranged from 58% to 83%. The N2O flux and NO3 −-N concentrations were significantly correlated to the growth of AOB, rather than AOA. This study confirms the importance of AOB in nitrification and the effect of DCD in inhibiting AOB growth and in decreasing N2O emissions in grazed pasture soils under field conditions. [Copyright &y& Elsevier]

Abstract: Integration of a restricted grazing regime in winter with the use of a nitrification inhibitor can potentially reduce N2O emissions from grazed pasture systems. A three year field study was conducted to compare annual N2O emission rates from a “tight nitrogen” grazed farmlet with those from a control farmlet. The control farmlet was managed under a conventional rotational all-year grazing regime, while the “tight nitrogen” farmlet was under a similar grazing regime, except during winter and early spring seasons when cows grazed for about 6h per day. A nitrification inhibitor (dicyandiamide, DCD) was applied onto the “tight nitrogen” farmlet immediately after grazing through winter and early spring. A chamber technique was used to measure N2O emissions in several paddocks from each farmlet during three contrasting seasons each year. The IPCC (Intergovernmental Panel on Climate Change) inventory methodology was used to estimate CH4 and indirect N2O emissions and the life cycle assessment (LCA) methodology was used to calculate CO2 emissions from the farm systems. The individual and combined effects of restricted grazing and DCD use on N2O emissions were also determined. During the late spring/summer and autumn periods, N2O emission rates were generally similar between the two farmlets. The use of a restricted grazing regime and DCD reduced N2O emissions from the grazed farmlet during the winter/early spring seasons by 43–55%, 64–79% and 45–60% over each of the three years, respectively. The use of restricted grazing and DCD both resulted in a similar reduction in N2O emissions, but there was no significant further reduction from the combination of these technologies. For the three study years, the annual N2O emission rate from the “tight nitrogen” farmlet was 20% lower, on average, than from the control. Total annual greenhouse gas (GHG) emissions, however, were only 5% less in the “tight nitrogen” system. [Copyright &y& Elsevier]

Abstract: This field study evaluated the effects of applying a combination of urease (UI) and nitrification inhibitors (NI) on ammonia (NH3) and nitrous oxide (N2O) emission from urine patches, using zeolite, single superphosphate (SSP) and urea fertilizer as a carrier. The trial was conducted on a Typic Haplustepts silt loam soil, near Lincoln, Canterbury, New Zealand during 2009–11. The treatments in 2009 included: a control (no urine or inhibitor), urine alone at 600kgNha−1, and urine with either double inhibitor (DI) a mixture (1:7 ratio w/w) of UI (N-(n-butyl) thiophosphoric triamide (nBTPT — trade name Agrotain®) and NI, dicyandiamide (DCD) or DCD alone at 10kgha−1 using zeolite and SSP as carriers. In 2010 trials, both zeolite and urea were used as carriers for DI and DCD. DI-zeolite and DI-urea were equally effective and reduced the average NH3 losses from applied urine over two years by 34.6% in autumn and 40% in spring respectively. The nBTPT in DI-SSP was decomposed by the free acid produced during its dissolution and therefore increased NH3 emission as does DCD alone. DCD consistently increased NH3 emissions by 39% and 15.6% in autumn and spring respectively. Spring application resulted in NH3–N losses of 16.9% as a percentage of the total N applied compared to 8.4% in autumn. Over the two years, the DI reduced N2O emissions by 53% in autumn and 46% in spring over urine alone treatment; the equivalent reductions for DCD were 42% and 39% for autumn and spring, respectively. These results suggest that applying DI in autumn and spring using zeolite or urea carrier five days prior to grazing has the most potential to reduce NH3 and N2O losses from specific urination event than using DCD alone; and therefore warrants further research to improve its longevity. [Copyright &y& Elsevier]

Abstract: A field experiment was conducted to evaluate the influences of long-term applications of organic amendments and chemical fertilizers on nitrous oxide (N2O) emissions from Mollisols in northeast China and to relate soil N2O fluxes to soil moisture and temperature. A closed-chamber method was used to determine soil N2O flux during the maize growing season in 2011. In the entire maize growing period, cumulative N2O emissions were significantly (all P <0.05) increased by 66, 86 and 83% under the applications of 4.5Mgha−1 maize straw combined with NPK, 7.5 and 22.5Mgha−1 pig manure combined with NPK, respectively, compared with the control (0.64±0.01kgN2O-Nha−1), whereas NPK fertilizer alone and 2.25Mgha−1 maize straw combined with NPK had no remarkable influences (P >0.05). Nonetheless, even increasing nitrogen inputs, the cumulative microbial N2O emission over 126days had an upper threshold around 1.2kgN2O-Nha−1. Approximately 25–44% of N2O was emitted from the applied organic amendments, and the emission factor (EF) of applied organic amendments as N2O based on 126days was between 0.07 and 1.52%, higher than NPK fertilizer-induced EF (0.03%). Soil temperature explained 38–96% of the seasonal variation in soil N2O fluxes using exponential models, with a Q 10 of 2.01–3.48. Our results suggest that the influences of organic amendments on soil N2O emissions from Mollisols primarily vary with the type of the applied organic amendments, whereas great nitrogen inputs at maximum asymptotically double baseline cumulative emissions. [Copyright &y& Elsevier]