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Abstract: Environmental conditions and agricultural management events affect the availability of substrates and microbial habitat required for the production and consumption of nitrous oxide (N2O), influencing the temporal and spatial variability of N2O fluxes from soil. In this study, we monitored for diurnal and event-related patterns in N2O emissions in the field, evaluated how substrate availability influenced denitrification, and assessed N2O reduction potential following major events in two tomato (Lycopersicon esculentum) management systems on clay loam soils: 1) conventional (sidedress fertilizer injection, furrow irrigation, and standard tillage) and 2) integrated (fertigation, subsurface drip irrigation, and reduced tillage). Potential denitrification activity, substrate limitation, and reduction to N2 were measured with an anaerobic slurry technique. In the field, we found no consistent diurnal patterns. This suggests that controlling factors that vary on an event-basis overrode effects of diurnally variable controls on N2O emissions. The lack of consistent diurnal patterns also indicates that measuring N2O emissions once per day following major events is sufficient to adequately assess annual N2O emissions in those systems. Nitrous oxide emissions varied per event and across functional locations in both systems. This illustrates that mechanisms underlying N2O emissions vary at relatively small temporal and spatial scales and demonstrates the importance of studying N2O emissions in the context of events and functional locations. In the conventional system, N2O fluxes were high [74.2±43.9–390.5±90.1μgN2O-Nm−2 h−1] and N2O reduction potential was significant. Both management systems exhibited carbon limitation on denitrification rates; and rates were N limited in the third fertigation event in the integrated system. Our findings suggest that denitrification is strongly contributing to high N2O emissions in conventional tomato cropping systems in California. Hence, management practices that reduce the conditions that favor denitrification, such as subsurface drip irrigation, are promising strategies for N2O reduction. [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]

Abstract: Nitrous oxide (N2O) emissions from Vertisols and Alfisols during sweet sorghum cultivation in the Indian semi-arid tropics were determined using a closed chamber technique during the rainy season (June–October) of 2010. The study included two treatments, nitrogen (N) at a rate of 90kg/ha and a control without N fertilizer application. The N2O emissions strongly coincided with N fertilization and rainfall events. The cumulative N2O–N emission from Alfisols was 1.81N2O–Nkg/ha for 90 N treatment and 0.15 N2O–Nkg/ha for the 0 N treatment. Similarly, the N2O–N emission from Vertisols was 0.70 N2O–Nkg/ha for 90 N treatment and 0.09 N2O–Nkg/ha for the 0 N treatment. The mean N2O–N emission factor for fertilizer induced emissions from the Alfisols was 0.90% as compared to 0.32% for Vertisols. Our results suggest that the N2O emissions are dependent on the soil properties. Therefore, the monitoring of N2O emissions from different agro-ecological regions, having different soil types, rainfall characteristics, cropping systems and crop management practices are necessary to develop comprehensive and accurate green house gas inventories. [Copyright &y& Elsevier]

Abstract: Carbon (C), nitrogen (N) and phosphorous (P) burial rates were determined within natural saltmarsh (NSM) and ‘managed realignment’ (MR) sediments of the Blackwater estuary, UK. Methane (CH4) and nitrous oxide (N2O) fluxes were measured along with their ability to offset a portion of the C burial to give net C sequestration. C and N densities (Cρ and Nρ) of NSM sediments (0.022 and 0.0019gcm−3) are comparable to other UK NSM sediments. Less vegetationally developed MR sediments have lower Cρ and Nρ (0.012 and 0.0011gcm−3) while the more vegetationally developed sites possess higher Cρ and Nρ (0.023 and 0.0030gcm−3) than NSM. Both NSM and MR areas were small CH4 (0.10–0.40gm−2 yr−1) and N2O (0.03–0.37gm−2 yr−1) sources. Due to their large Global Warming Potentials, even these relatively small greenhouse gas (GHG) fluxes reduced the net C sequestration within MR marshes by as much as 49%, but by only 2% from NSM. Potential MR areas within the Blackwater estuary (29.5km2 saltmarsh and 23.7km2 intertidal mudflat) could bury 5478tCyr−1 and 695.5tN yr−1, with a further 476tNyr−1 denitrified. The saltmarsh MR would also sequester 139.4t Pyr−1. GHG fluxes would reduce the C burial benefit by 24% giving a C sequestration rate of 4174tCyr−1. Similar areas within the Humber estuary (74.95km2) could bury 3597tCyr−1 and 180tNyr−1, with a further 442tNyr−1 denitrified. GHG fluxes would reduce the C burial benefit by 31% giving a C sequestration rate of 2492t Cyr−1. Overall, MR sites provide sustainable coastal defence options with significant biogeochemical value and, despite being net sources of CH4 and N2O, can sequester C and reduce estuarine nutrient loads. [Copyright &y& Elsevier]

Abstract: Measurements of methane (CH4) and nitrous oxide (N2O) fluxes have been extensively taken following rice seedlings transplanted into paddy fields, while little is known about CH4 and N2O fluxes from rice seedling nurseries. Fluxes of CH4 and N2O were simultaneously measured in rice seedling nurseries under the water regimes of continuous flooding and moist irrigation without waterlogging in Southeast China in 2010. Fluxes of CH4 and N2O from continuously flooded nurseries averaged 10.33–14.84mgm−2 h−1 and 28.64–34.35μg N2O–Nm−2 h−1 for the different fertilizer applied plots, respectively. Relative to continuous flooding, moist irrigation decreased total CH4 by 14–50% but increased N2O by 72–186%, dependent on the fertilizer types. Compared with inorganic N fertilizer, organic manure application increased CH4 by 44% and 148% in the continuously flooded and moist irrigation nurseries, respectively. Rice seedling growth parameters were the greatest in moist irrigation nurseries with inorganic N fertilizer application. Moist irrigation instead of continuous waterlogging and shifts from organic manure to combined organic/inorganic N fertilizer inputs have been increasingly experienced in Chinese rice seedling nurseries, which would benefit for mitigating the combined global warming potentials of CH4 and N2O from rice seedling nurseries in China. [Copyright &y& Elsevier]

Abstract: To evaluate global warming potential (GWP) on livestock waste treatment and biomass production in rice field, methane (CH4) and nitrous oxide (N2O) fluxes from forage rice fields planted with 4 different cultivars (Oryza sativa L. cv. Hamasari, Leafstar, Kusahonami and Takanari) were measured. Each of the cultivars were subjected either to basal fertilization alone (control plots) (84kgNha−1), or to basal fertilization plus topdressing with liquid cattle waste or LCW (treatment plots) (567kgNha−1). Liquid cattle waste application to the rice field resulted in peak CH4 fluxes ranging from 22.0 to 32.1mgm−1 h−1 during flooded conditions and large N2O fluxes ranging from 526 to 8591μgm−1 h−1 after midsummer drainage and final drainage. The GWP of the control plots was between 1358 and 3872kgCO2eqha−1, while the treatment plots ranged between 4503 and 8426kgCO2eqha−1 and more than 60% of the GWP was from the N2O emission in treatment plots. In both the control and treatment plots, the lowest GWPs per ton of above-ground biomass were found to be from the Leafstar cultivar, which had a higher aboveground biomass than other cultivars; 117kgCO2eqt−1 from the control and 257kgCO2eqt−1 from the treatment plots. Thus, both forage production and suitable disposal of the LCW may be able to be achieved concomitantly with lower levels of GWP by cultivation of Leafstar in our field. [Copyright &y& Elsevier]

Abstract: Freshwater lakes are known to release carbon dioxide (CO2) and methane (CH4) to the atmosphere; however, the importance of lakes in global nitrous oxide (N2O) budgets is not yet known. Further, despite the abundance of small lakes on the landscape, neither emissions of these gases nor their drivers are well described. Dissolved concentrations of CO2, CH4 and N2O greenhouse gases were related to water chemistry, hydrology and catchment characteristics in order to identify factors controlling gas concentrations for 121 small Irish headwater lakes (median area: 2.0ha) in relatively undisturbed catchments; lake–atmosphere gas fluxes were also calculated. The majority of lakes were supersaturated (relative to the atmosphere) with CO2 and N2O while CH4 was above saturation in all lakes. Dissolved gas concentrations were correlated with land cover (rock, forest and grassland), deuterium excess (an indicator of hydrologic character) and lake organic carbon concentrations, although dissolved CO2 exhibited few significant relationships. Principal components analysis indicated that higher levels of CH4 and N2O supersaturation were exhibited under different conditions. Methane supersaturation was highest in low elevation catchments with an evaporative hydrologic character and high organic carbon concentrations. In contrast, lakes characteristic of N2O supersaturation were low in carbon and located in more rapidly flushed higher elevation catchments. Estimated fluxes of CO2, CH4 and N2O to the atmosphere averaged 14, 0.36 and 1.3×10−3 mmolm−2 d−1, respectively. [Copyright &y& Elsevier]

Abstract: Nitrous oxide (N2O) is a significant greenhouse gas with a global warming potential that is 300 times than that of carbon dioxide. Soil derived N2O emissions usually display a high degree of spatial and temporal variability because of their dependence on soil chemical and physical properties, and climate dependent environmental factors. However, there is little research that incorporates spatial dependence in the estimation of N2O emissions allowing for environmental factors in the same model. This study aims to examine the impact of two environmental factors (soil temperature and soil moisture) on N2O emissions and explore the spatial structure of N2O in the sub-tropical South East Queensland region of Australia. The replicated data on N2O emissions and soil properties were collected at a typical sugarcane land site covering 25 uniform grid points across 3600m2 between October 2007 and September 2008. A Bayesian conditional autoregressive (CAR) model was used to model spatial dependence. Results showed that soil moisture and soil temperature appeared to have substantially different effects on N2O emissions after taking spatial dependence into account in the four seasons. There was a substantial variation in the spatial distribution of N2O emission in the different seasons. The high N2O emission regions were accompanied by high uncertainty and changed in varying seasons in this study site. Spatial CAR models might be more plausible to elucidate and account for the uncertainty arising from unclear variables and spatial variability in the assessment of N2O emissions in soils, and more accurately identify relationships with key environmental factors and help to reduce the uncertainty of the soil parameters. [Copyright &y& Elsevier]

Abstract: Riparian wetlands bordering intensively managed agricultural fields can act as biological filters that retain and transform agrochemicals such as nitrate and pesticides. Nitrate removal in wetlands has usually been attributed to denitrification processes which in turn imply the production of greenhouse gases (CO2 and N2O). Denitrification processes were studied in the Salburua wetland (northern Spain) by using undisturbed soil columns which were subsequently divided into three sections corresponding to A-, Bg- and B2g-soil horizons. Soil horizons were subjected to leaching with a 200mgNO3 − L−1 solution (rate: 90mLday−1) for 125days at two different temperatures (10 and 20°C), using a new experimental design for leaching assays which enabled not only to evaluate leachate composition but also to measure gas emissions during the leaching process. Column leachate samples were analyzed for NO3 − concentration, NH4 + concentration, and dissolved organic carbon. Emissions of greenhouse gases (CO2 and N2O) were determined in the undisturbed soil columns. The A horizon at 20°C showed the highest rates of NO3 − removal (1.56mgN–NO3 − kg−1 DWsoilday−1) and CO2 and N2O production (5.89mgCO2 kg−1 DWsoilday−1 and 55.71μgN–N2Okg−1 DWsoilday−1). For the Salburua wetland riparian soil, we estimated a potential nitrate removal capacity of 1012kgN–NO3 − ha−1 year−1, and potential greenhouse gas emissions of 5620kgCO2 ha−1 year−1 and 240kgN–N2Oha−1 year−1. [Copyright &y& Elsevier]

Abstract: The atmospheric fluxes of N2O, CH4 and CO2 from the soil in four mangrove swamps in Shenzhen and Hong Kong, South China were investigated in the summer of 2008. The fluxes ranged from 0.14 to 23.83μmolm− 2 h− 1, 11.9 to 5168.6μmolm− 2 h− 1 and 0.69 to 20.56mmolm− 2 h− 1 for N2O, CH4 and CO2, respectively. Futian mangrove swamp in Shenzhen had the highest greenhouse gas fluxes, followed by Mai Po mangrove in Hong Kong. Sha Kong Tsuen and Yung Shue O mangroves in Hong Kong had similar, low fluxes. The differences in both N2O and CH4 fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N2O and CO2 fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH4 +-N contents, as well as the soil porosity. However, only soil NH4 +-N concentration had significant effects on CH4 fluxes. [Copyright &y& Elsevier]

Abstract: Annual paddy rice–winter wheat rotation constitutes one of the typical cropping systems in southeast China, in which various water regimes are currently practiced during the rice-growing season, including continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding and moisture but without waterlogging (F-D-F-M). We conducted a field experiment in a rice–winter wheat rotation system to gain an insight into the water regime-specific emission factors and background emissions of nitrous oxide (N2O) over the whole annual cycle. While flooding led to an unpronounced N2O emission during the rice-growing season, it incurred substantial N2O emission during the following non-rice season. During the non-rice season, N2O fluxes were, on average, 2.61 and 2.48mg N2O–Nm− 2 day−1 for the 250kg N ha−1 applied plots preceded by the F and F-D-F water regimes, which are 56% and 49% higher than those by the F-D-F-M water regime, respectively. For the annual rotation system experienced by continuous flooding during the rice-growing season, the relationship between N2O emission and nitrogen input predicted the emission factor and background emission of N2O to be 0.87% and 1.77kg N2O–Nha−1, respectively. For the plots experienced by the water regimes of F-D-F and F-D-F-M, the emission factors of N2O averaged 0.97% and 0.85%, with background N2O emissions of 2.00kg N2O–Nha−1 and 1.61kg N2O–Nha−1 for the annual rotation system, respectively. Annual direct N2O–N emission was estimated to be 98.1Gg yr−1 in Chinese rice-based cropping systems in the 1990s, consisting of 32.3Gg during the rice-growing season and 65.8Gg during the non-rice season, which accounts for 25–35% of the annual total emission from croplands in China. [Copyright &y& Elsevier]

Addition of different forms of nitrogen fertilizer to cultivated soil is known to affect carbon dioxide (CO2) and nitrous oxide (N2O) emissions. In this study, the effect of urea, wastewater sludge and vermicompost on emissions of CO2 and N2O in soil cultivated with bean was investigated. Beans were cultivated in the greenhouse in three consecutive experiments, fertilized with or without wastewater sludge at two application rates (33 and 55 Mg fresh wastewater sludge ha¿1, i.e. 48 and 80 kg N ha¿1 considering a N mineralization rate of 40%), vermicompost derived from the wastewater sludge (212 Mg ha¿1, i.e. 80 kg N ha¿1) or urea (170 kg ha¿1, i.e. 80 kg N ha¿1), while pH, electrolytic conductivity (EC), inorganic nitrogen and CO2 and N2O emissions were monitored. Vermicompost added to soil increased EC at onset of the experiment, but thereafter values were similar to the other treatments. Most of the NO3 ¿ was taken up by the plants, although some was leached from the upper to the lower soil layer. CO2 emission was 375 C kg ha¿1 y¿1 in the unamended soil, 340 kg C ha¿1 y¿1 in the urea-amended soil and 839 kg ha¿1 y¿1 in the vermicompost-amended soil. N2O emission was 2.92 kg N ha¿1 y¿1 in soil amended with 55 Mg wastewater sludge ha¿1, but only 0.03 kg N ha¿1 y¿1 in the unamended soil. The emission of CO2 was affected by the phenological stage of the plant while organic fertilizer increased the CO2 and N2O emission, and the yield per plant. Environmental and economic implications must to be considered to decide how many, how often and what kind of organic fertilizer could be used to increase yields, while limiting soil deterioration and greenhouse gas emissions. [Copyright &y& Elsevier]

Abstract: The emission of N2O from China is globally significant, but relatively few direct observations have been made in many of the fresh water environments most likely to be important sites of N2O production. In this paper, N2O saturations were examined in the ecologically heterogeneous, eutrophied, Lake Taihu, as well as in surrounding rivers in eastern China. The emissions of N2O were estimated and compared with those from other landscapes within the Lake Taihu drainage basin. We found that anthropogenically-enhanced inorganic N inputs act as a limited primary control on the spatial distribution of N2O saturations in heavily eutrophied parts of the lake only and that overall, lake N2O production and emission are not raised as significantly as expected due to high N inputs. In comparison, the heavily eutrophied river network is an important fraction of the local N2O budget, and when considered together with emissions of N2O from the lake, constitute a major (10–50% depending on season) fraction of total N2O emissions from the Lake Taihu drainage basin. [Copyright &y& Elsevier]

In 2001 and 2002, fluxes of N2O, CH4, CO2 and N2 were measured in two constructed wetlands (CW) for domestic wastewater treatment in Estonia. The difference between the median values of N2O, CH4, and N2 fluxes in the horizontal subsurface flow (HSSF) CWs was non-significant, being 1.3–1.4 and 1.4–4.1 mg m−2 d−1 for N2O–N and CH4–C, and 0.16–0.17 g N m−2 d−1 for N2–N respectively. The CO2–C flux was significantly lower (0.6 g C m−2 d−1) in one of the HSSF filters of a hybrid CW, whereas the single HSSF and VSSF filters emitted 1.7 and 2.0 g C m−2 d−1. The median value of CH4–C emission in CWs varied from 1.4 to 42.6 g C m−2 d−1, being significantly higher in the VSSF filter beds. We also estimated C and N budgets in one of the HSSF CWs (312.5 m2) for 2001 and 2002. The total C input into this system was similar in 2001 and 2002, 772 and 719 kg C year−1, but was differently distributed between constituent fluxes. In 2001, the main input flux was soil and microbial accumulation (663 kg C year−1 or 85.8% of total C input), followed by plant net primary production (NPP) (10.2%) and wastewater inflow (3.9%). In 2002, 55.7% of annual C input was bound in plant NPP, whereas the increase in soil C formed 28.5% and wastewater inflow 15.7%. The main C output flux was soil respiration, including microbial respiration from soil and litter, and the respiration of roots and rhizomes. It formed 120 (97.5%) and 230 kg C year−1 (98.2%) in 2001 and 2002 respectively. The measured CH4–C flux remained below 0.1% of total C output. The HSSF CW was generally found to be a strong C sink, and its annual C sequestration was 649 and 484 kg C year−1 per wetland in 2001 and 2002 respectively. However, negative soil and microbial accumulation values in recent years indicate decreasing C sequestration. The average annual N removal from the system was 38–59 kg N year−1 (46–48% of the initial total N loading). The most important flux of the N budget was N2–N emission (22.7 kg in 2001 and 15.2 kg in 2002), followed by plant belowground assimilation (2.3 and 11.9 kg N year−1 in 2001 and 2002), and above-ground assimilation (1.9 and 9.2 kg N year−1, respectively). N2O emission was low: 0.37–0.60 kg N year−1 . [Copyright &y& Elsevier]

In this paper we investigate the impact of nitrate (NO3>> −) concentration and temperature on the production of carbon dioxide (CO2>>), methane (CH4>>) and nitrous oxide (N2O). We studied sediment collected during spring, summer and autumn from a constructed pond in South Sweden. Homogenised sediment samples were dark incubated in vitro under N2>> atmosphere at 13 °C and 20 °C after addition of five NO3>> − concentrations, between 0 and 16 mg NO3>> −–N per litre. We found higher net production of N2O and CO2>> at the higher temperature. Moreover, increased NO3>> − concentrations had strong positive impact on the N2O concentration, but no effect on CH4>> and CO2>> production. The lack of response in CO2>> is suggested to be due to the use of alternative oxidants as electron acceptors. Interaction between NO3>> − and temperature suggests a further increase of N2O net production when both NO3>> − and temperature are high. Our interpretation of the CH4>> data is that at high concentrations of NO3>> − temperature is of less importance for CH4>> production. We also found that at 13 °C CH4>> production was substrate limited and that the addition of acetate increased CH4>> as well as CO2>> production. There was a seasonal effect on gas production potential, with more CH4>> and N2O produced in spring than in summer. Re-calculation of the gas concentrations into global warming potential (GWP) units (i.e. CO2>>, CH4>>, and N2O transferred to CO2>> equivalents) shows that GWP increases with temperature. However, under environmental conditions generally occurring in South Swedish ponds, i.e. low temperature and high NO3>> − concentration during spring and high temperature and low NO3>> − concentration during summer, NO3>> − concentration is of minor importance. [Copyright &y& Elsevier]

The Skjønhaug constructed wetland (CW) is a free surface water (FSW) wetland polishing chemically treated municipal wastewater in southeastern Norway and consists of three ponds as well as trickling, unsaturated filters with light weight aggregates (LWA). Fluxes of nitrous oxide (N2O) and methane (CH4) have been measured during the autumn, winter and summer from all three ponds as well as from the unsaturated filters. Physicochemical parameters of the water have been measured at the same localities. The large temporal and spatial variation of N2O fluxes was found to cover a range of −0.49 to 110 mg N2O–N m−2 day−1, while the fluxes of CH4 was found to cover a range of −1.2 to 1900 mg m−2 day−1. Thus, both emission and consumption occurred. Regarding fluxes of N2O there was a significant difference between the summer, winter and autumn, with the highest emissions occurring during the autumn. The fluxes of CH4 were, on the other hand, not significantly different with regard to seasons. Both the emissions of N2O and CH4 were positively influenced by the amount of total organic carbon (TOC). The measured fluxes of N2O and CH4 are in the same range as those reported from other CWs treating wastewater. There was an approximately equal contribution to the global warming potential from N2O and CH4. [Copyright &y& Elsevier]

In this paper, three unregulated components, ammonia, nitrous oxide and hydrogen cyanide, emitted from five passenger vehicles are investigated. With focus upon emission factors from existing production technology, vehicles produced between 1989 and 1998 with considerable mileage (7000 to 280,000) are chosen. Among the five vehicles, four were sold in the European market, whereas one was sold in the US market.The vehicles are tested on a chassis dynamometer. An EU2000 Driving Cycle (NEDC) and a US Urban Driving Cycle (UDC) of the Federal Test Procedure 75 (FTP-75) are used in the study. The regulated emissions are measured using a Horiba Mexa series. Unregulated emissions, ammonia (NH3), nitrous oxide (N2O) and hydrogen cyanide (HCN) are analysed by mass spectrometer, gas chromatography and CNT-NA, TIM315-74W method, respectively. Both the unregulated emissions and the regulated emissions show driving cycle dependency; and they are also improved with newer vehicle and emission control technology. However, a gasoline direct injection vehicle (relatively new technology in this study) has rather high regulated emissions, whereas the NH3, N2O and HCN emissions are low. [Copyright &y& Elsevier]

Sources and sinks of the atmospherically reactive gas nitrous oxide (N2O) were determined in the heavily nutrient loaded Childs River in Cape Cod, MA. Surface waters were supersaturated and bottom waters were depleted with N2O throughout the system. In apparent septic effluent plumes, N2O concentrations reached 3 orders of magnitude above atmospheric equilibrium. Because nitrate and N2O concentrations correlated in groundwater entering the estuary, septic tank effluent appeared responsible for the supersaturated concentrations of N2O in surface waters. A hyperbolic function fit nitrate and N2O concentrations in the water column of the estuary with a maximum supersaturation of approximately 60 nM. From surface water supersaturation we predicted a release of 480 nmol N2O m−2 h−1 to the atmosphere in the summer. Property plots of salinity vs. bottom-water N2O suggested a benthic sink of N2O. Consistent with this trend, sediments consumed rather than released N2O in most flux measurements. Nutrient loading did not directly alter benthic N2O flux, potentially because stratification limited exposure of sediments to nitrate-rich surface waters, but macroalgal cover increased benthic N2O consumption. Sediment N2O consumption averaged 111 nmol N2O m−2 h−1 and correlated with oxygen uptake. Losses from the system to the atmosphere and sediments exceeded inputs of N2O contaminated groundwater, which suggests missing N2O sources. [Copyright &y& Elsevier]

In recent years, worldwide concern over global warming has been expressed. It has been reported that domestic wastewater and its treatment processes are sources of CH4 and N2O, designated as greenhouse gases, the reduction of which was noted to be extremely important at the Third Conference of the Framework Convention on Climate Change (Conference Of the Parties; COP3). Here we report a study of a field that has been unexplored until now: analytical evaluation of the properties of the emission of CH4 and N2O and methods of restricting their emission in soil-trench wastewater treatment processes, the use of which is spreading, mainly in developing nations. The results have provided the following information. A field fact-finding survey has confirmed that soil trenches emit 9.3–13.9 g CH4 m−3 and 8.2–12.2 gN2O m−3 in Japan, and 3.0–4.5 g CH4 m−3 and 3.3–5.0 g N2O m−3 in China. The emission properties widely vary according to the structure of the treatment system. The conversion ratio for nitrogen in the wastewater influent to N2O by a soil trench is between 2 and a maximum of 8%, and ranges from a few- to several 10-fold as much as that with the activated sludge method, suggesting that this can be a large source of N2O emission. It has also clearly been shown that the aerobic–anaerobic state inside the treatment system is closely related to its CH4 and N2O emission characteristics. By performing ventilation to maintain the oxidation–reduction potential (ORP) near the trench at an aerobic condition of +200 mV or more, the quantities of CH4 and N2O emitted can be reduced by as much as 50% from the levels without this ventilation, and that this can make a large contribution. [Copyright &y& Elsevier]

This paper reviews existing on-farm GHG accounting models for dairy cattle systems and their ability to capture the effect of dietary strategies in GHG abatement. The focus is on methane (CH 4) emissions from enteric and manure (animal excreta) sources and nitrous oxide (N 2 O) emissions from animal excreta. We identified three generic modelling approaches, based on the degree to which models capture diet-related characteristics: from 'none' (Type 1) to 'some' by combining key diet parameters with emission factors (EF) (Type 2) to 'many' by using process-based modelling (Type 3). Most of the selected on-farm GHG models have adopted a Type 2 approach, but a few hybrid Type 2 / Type 3 approaches have been developed recently that combine empirical modelling (through the use of CH 4 and/or N 2 O emission factors; EF) and process-based modelling (mostly through rumen and whole tract fermentation and digestion). Empirical models comprising key dietary inputs (i.e., dry matter intake and organic matter digestibility) can predict CH 4 and N 2 O emissions with reasonable accuracy. However, the impact of GHG mitigation strategies often needs to be assessed in a more integrated way, and Type 1 and Type 2 models frequently lack the biological foundation to do this. Only Type 3 models represent underlying mechanisms such as ruminal and total-tract digestive processes and excreta composition that can capture dietary effects on GHG emissions in a more biological manner. Overall, the better a model can simulate rumen function, the greater the opportunity to include diet characteristics in addition to commonly used variables, and thus the greater the opportunity to capture dietary mitigation strategies. The value of capturing the effect of additional animal feed characteristics on the prediction of on-farm GHG emissions needs to be carefully balanced against gains in accuracy, the need for additional input and activity data, and the variability encountered on-farm. Unlabelled Image • The effect of diet chemistry on GHG emissions from dairy is often poorly understood. • The capture of diet-related characteristics ranges from 'none' to 'some' to 'many'. • The closer the model to rumen function, the closer to diet-related GHG abatement • All models can improve their ability to predict GHG emissions from ruminant systems. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) is an important greenhouse gas. Its atmospheric concentration have increased with the industrialisation and the use of N fertilizer. The contribution of freshwater systems to N 2 O emissions is still very uncertain, while regional transfer of nitrogen depends on soil and hydrology. Riverine and spring N 2 O dissolved in water was therefore measured over two years in the 3453 km2 Haut-Loir watershed (France). This temperate cropland watershed is characterized by two different hydrological systems east and west of the Loir River. The eastern rivers, fed by the emergence of the deep Beauce aquifer, exhibited significantly higher dissolved N 2 O concentrations (Beauce region, mean: 2.93 μg-N L−1) than the western rivers (Perche region, mean: 0.87 μg-N L−1), which were largely influenced by runoff during winter flooding. The eastern rivers had large nitrate concentrations all over the year; in the Perche, nitrate underwent a seasonal cycle with large loads during winter floods, but there were no consistent seasonal patterns in N 2 O. The ratios of N 2 O in excess of equilibrium on nitrate, often used as a proxy of emission factor (EF), were much smaller than the default IPCC values, both for rivers (0.014% versus 0.25% for IPCC EF 5r) and the Loir spring (0.085% versus 0.6% for the IPCC EF 5g for groundwater and springs). EF 5r were significantly different between the two parts of the watershed only in winter, because of the seasonal variability of NO 3 −. Moreover dissolved N 2 O is controlled not only by NO 3 −, as it is considered in the calculation of the EF 5 , but also by water pH and dissolved organic carbon. A good prediction of dissolved N 2 O was obtained using these physicochemical variables and hydrological regions. Thus, these results suggest that the spatial variability of riverine N 2 O depends on local hydrology, while further research is needed to understand the seasonal variability. Unlabelled Image • Dissolved N 2 O was measured in surface water in a watershed with contrasting hydrology. • Hydrology drives the differences in nitrate dynamics in rivers. • N 2 O was higher in rivers fed by aquifer emergence than in rivers fed by surface runoff. • The ratio N 2 O/NO 3 −, a proxy of emissions factor, was 10 times lower than the IPCC value. [ABSTRACT FROM AUTHOR]

Cover cropping is beneficial for reducing soil erosion and nutrient losses, but there are conflicting reports on how cover cropping affects emissions of nitrous oxide (N 2 O), a potent greenhouse gas. In this study, we measured N 2 O fluxes over a full year in Illinois corn plots with and without rye cover crop. We compared these year-round measurements to N 2 O emissions predicted by the Intergovernmental Panel on Climate Change (IPCC) Tier 1 equation and the Denitrification-Decomposition (DNDC) model. In addition, we measured potential denitrification and N 2 O production rates. The field measurements showed typical N 2 O peaks shortly after fertilizer application, as well as a significant late-winter peak. Cover cropping significantly reduced all peak N 2 O fluxes, with decreases ranging from 39 to 95%. Neither model was able to accurately predict annual N 2 O fluxes or the decrease in N 2 O emissions from cover-cropped fields. In contrast to field measurements, lab assays found that cover cropping significantly increased potential denitrification by 90–127% and potential N 2 O production by 54–106%. The rye cover-cropped plots had lower soil nitrate and higher soil carbon. When limiting nitrate and excess carbon were provided in lab assays, the proportion of N 2 O resulting from denitrification decreased. These results suggest that the discrepancy between the observed decrease in field N 2 O emissions and the increase in denitrification potential may be due to the difference in available nutrients between the field and laboratory measurements. Overall, these results suggest the importance of late-winter peaks in N 2 O emissions and the potential of rye cover cropping to reduce N 2 O emissions from agricultural fields. Unlabelled Image • Assessed cover cropping effects on agricultural nitrous oxide emissions • Conducted field and laboratory measurements of soils and gases and modeling • Rye cover cropping showed potential to reduce nitrous oxide emissions. • Models did not consistently predict the observed decrease in emissions. • Cover cropping increased denitrifying and nitrous oxide production potential in lab. [ABSTRACT FROM AUTHOR]

A thorough elucidation of the coupled effects of N fertilization and straw incorporation on N 2 O emissions and N losses is crucial for alleviating negative environmental impacts in intensively farmed regions. Here, we conducted an in situ 15N tracing experiment to assess the source of N 2 O emissions and fate of fertilizer-N in soil intensively farmed with summer maize (Zea mays L.). Four treatments, i.e., no N fertilization and no straw incorporation (N0S0), straw incorporation only (N0S1), N fertilization only (N1S0), and N fertilization plus straw incorporation (N1S1), were established in the study. Compared with straw removal, straw incorporation increased the seasonal N 2 O emissions by 22.3% but reduced the N 2 O emissions per unit of applied N by 6.22% (P > 0.05). The emission of fertilizer-derived N 2 O occurred mainly in the 13–17 days after fertilization; thereafter, the ratio of fertilizer-derived N 2 O fluxes would be less than 5%. N fertilization significantly stimulated non-fertilizer-derived N 2 O emissions and soil CO 2 fluxes, especially when straw was incorporated (P < 0.05), indicating that N fertilization might have triggered the mineralization of straw-N and/or native soil organic N. The soil NO 3 −-N concentration in straw-incorporated plots tended to be lower than that in straw-removed plots, especially after N fertilization events. Straw incorporation sequestered 52.5% (27.4 kg N ha−1) more fertilizer-N in 1 m of soil than straw removal (P < 0.05) while significantly increasing the fertilizer-N harvest index and maintaining grain yield. Overall, compared with straw removal, straw incorporation significantly reduced total fertilizer-N losses (by 12.8%, i.e., 14.58 kg N ha−1; P < 0.05). Our study highlights the benefits of straw incorporation for increasing in-season and multiseason fertilizer-N use efficiencies and alleviating fertilizer-N-induced environmental costs in intensively farmed regions. Unlabelled Image • Straw incorporation alleviated N 2 O emissions per unit of applied N. • N fertilizer applied with crop straw enhanced non-fertilizer-derived N 2 O emissions. • Straw incorporation increased soil N retention and reduced fertilizer-N losses. • Straw incorporation tended to enhance in-season and multiseason N use efficiency. [ABSTRACT FROM AUTHOR]

To increase soil carbon (C) stock, cover crop cultivation during the fallow season and its biomass incorporation as green manure (GM) is strongly suggested in mono-rice paddy. On the other hand, biomass application can highly increase greenhouse gas (GHG) emission, in particular methane (CH 4) during irrigated cropping season. Aerobic short pre-digestion of biomass applied soils was very effective to suppress CH 4 emission. However, its effect on other GHG (CO 2 and N 2 O) emissions was not clear. To assess the integrated influence of aerobic short pre-digestion of green manured soils on global warming impact, cover crop biomass as GM was amended with different time interval before flooding (0–30 days) and aerobically decomposed under upland condition. Aerobic short pre-digestion over 10 days significantly decreased seasonal CH 4 flux, but did not affect N 2 O emission. As aerobic pre-digestion days became longer, net ecosystem C balance (NECB) which implies the difference between C input and output was slightly increased, but not statistically different. The net primary productivity of rice plant as a C input source was not significantly differentiated by aerobic short pre-digestion. As a C output source, the respired C loss that was composed with CO 2 -C and CH 4 -C emission was not considerably discriminated among 0–30 days of aerobic short pre-digestion. As a consequence, due to big reduction of CH 4 emission, aerobic short pre-digestion significantly decreased net GWP which means integration of seasonal CH 4 and N 2 O fluxes and NECB as CO 2 equivalent. In conclusion, aerobic short pre-digestion of biomass applied soil could be a sustainable management practice to decrease GHG emission impact without SOC stock change in temperate rice paddy field. Unlabelled Image • Aerobic short pre-digestion of biomass amended paddy over 10 days significantly decreased CH 4 flux. • Aerobic short pre-digestion did not change N 2 O flux and soil C stock. • Aerobic short pre-digestion did not affect rice productivity. • Aerobic short pre-digestion significantly decreased net global warming potential. [ABSTRACT FROM AUTHOR]

Dung and urine patches on grasslands are hotspots of greenhouse gas (GHG) emissions in temperate regions, while its importance remains controversial for tropical regions as emissions seem to be lower. Here we investigated N 2 O, CH 4 and CO 2 emissions from urine and dung patches on tropical pastures in Kenya, thereby disentangling interactive and pure water, dung or urine effects. GHG fluxes were monitored with automated chambers for 42–59 days covering three seasons (short rainy season, long rainy season, dry season) for six treatments (Control; +1 L water; +1 kg dung; 1 L urine; 1 L water +1 kg dung; 1 L urine +1 kg dung). Cumulative CO 2 emissions did not differ among treatments in any of the seasons. Water or urine addition alone did not affect CH 4 fluxes, but these were elevated in all dung-related treatments. Scaled up on the total area covered, dung patches halve the CH 4 sink strength of tropical pastures during the dry season, while during the rainy season they may turn tropical pastures into a small CH 4 source. For N 2 O, both dung and urine alone and in combination stimulated emissions. While the N 2 O emission factor (EF N2O) from dung being constant across seasons, the EF N2O for urine was greater during the short rainy season than during the dry season. Combined application of urine + dung was additive on EF N2O. While the mean dung EF N2O in our study (0.06%) was similar to the IPCC Guidelines for National GHG Inventories EF N2O for dry climate (0.07%), the urine EF N2O we measured (0.03–0.25%) was lower than the IPCC value (0.32%). In addition, the IPCC Guidelines assume a urine-N: dung-N ratio of 0.66:0.34, which is higher than found for SSA (<0.50:0.50). Consequently, IPCC Guidelines still overestimate N 2 O emissions from excreta patches in SSA. Unlabelled Image • CH 4 emissions from dung patches may turn pastures from CH 4 sinks to sources. • N 2 O emissions add up if dung is deposited onto urine patches. • The urine EF N2O for dry climate by IPCC 2019 (0.32%) is likely too high. • Split of N in urine and dung is lower as in IPCC further lowering the excreta EF N2O. [ABSTRACT FROM AUTHOR]