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Organic fertilizers, such as manure and compost, are promising additions for synthetic fertilizers in order to increase soil fertility and crop yields. However, the organic fertilizers applied to soils may increase nitrous oxide (N 2 O, a greenhouse gas) emissions due to their lower C/N ratios, and therefore potentially contribute to global warming. Very few studies have used process-based models to assess the environmental advantages and drawbacks of compost soil amendments compared to other field treatments. In this study, the UK-DNDC model was modified for simulation of nitrous oxide (N 2 O) fluxes emitted from the soils treated with green compost and farmyard manure at three UK farms (WE, PW and NW): one winter wheat and two grasslands. The results show that the annual overall N 2 O emissions were 1.45 kg N ha −1  y −1 for WE treated with farmyard manure, 0.71 for WE with green compost, 1.09910 for PW treated with farmyard manure, 0.94 for PW treated with green compost, 1.19 for NW treated with farmyard manure, and 1.18 for NW treated with green compost. A two dimensional linear model was developed to correlate nitrogen loading and soil pH for calculations of emissions and emission factors (EFs). The linear model could fit the emissions obtained from the UK-DNDC model well. The squares of correlation coefficients of the emissions between two models are 0.993 and 0.985 for farmyard manure and green compost, respectively. Analysis of correlation coefficients between N 2 O emissions and air temperature, precipitation as well as the time period between fertilizer application and sample measurement (PFS) for the three sites treated with farmyard manure and compost indicated that N 2 O emissions were mainly related to PFS. The modified DNDC model provides an approach to estimating N 2 O emissions from compost amended soils. [ABSTRACT FROM AUTHOR]

Inland aquaculture ponds in China collectively cover 2.57 million ha, so emissions of the greenhouse gases methane (CH 4 ) and nitrous oxide (N 2 O) from these ponds may constitute a significant contribution to global warming. During 2016 and 2017, CH 4 and N 2 O fluxes and a range of pond-water and sediment properties were measured in replicated ( n  = 4) “mixed-fish” and “crab” aquaculture ponds in southeast China. Annual CH 4 and N 2 O emissions were 64.4 kg C ha −1 and 2.99 kg N ha −1 , respectively, from the “mixed-fish” ponds, and 51.6 kg C ha −1 and 3.32 kg N ha −1 , respectively, from the “crab” ponds. Emission differences between pond types were significant ( p  < 0.05) for both gases. CH 4 fluxes from the “crab” ponds were significantly increased by the presence of aquatic vegetation, but N 2 O fluxes were not affected. Emissions of N 2 O were estimated to be 0.54% and 0.71% of the total nitrogen input (in the feed) for the “mixed-fish” and “crab” ponds, respectively. The net economic benefit-scaled sustained-flux global warming potential (NEB-scaled SGWP) of the “crab” ponds was 61.6% higher ( p  < 0.05) than that of the “mixed-fish” pond. Our CH 4 and N 2 O emissions results suggest that aquaculture ponds can be important contributors to regional and national GHG inventories, with aquaculture type an important factor in total GHG impact. Further CH 4 and N 2 O flux research is needed at aquaculture ponds across China to better establish the range of potential GHG impacts, and to confirm the importance of the influencing factors identified in this study. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) contributes substantially to greenhouse gas (GHG) emissions in the agricultural and land-use sectors. Owing to the high effort needed for measuring N 2 O emissions and the resulting lack of sufficient field measurements to apply at country-wide scale, soil-borne N 2 O emissions are often estimated by applying published IPCC default emission factors. To examine the data reported in the national GHG inventory, the current study utilizes a large data set of soil C/N ratios to predict N 2 O emissions and their distribution from drained organic soils in Switzerland. Calculated emission rates increase in the order of forest < grassland < cropland, and they are similar to the mean values currently used in the inventory. Distributions of N 2 O emissions are highly positive-skewed and they reveal probabilities of 10 and 14% for cropland and grassland, respectively, to be above 20 kg of N 2 O-N per hectare and year. It is likely that the greater part of N 2 O from drained organic soil derives from N released upon peat decomposition, and not from fertilization. In conclusion, this research shows that measurement of soil C/N ratios improves the reliability of organic soil N 2 O emissions estimates on a national scale and identifies site conditions where future emission measurements would be most effective for reducing the uncertainty in the GHG inventory. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) is an important greenhouse gas and a catalyst of stratospheric ozone decay. Agricultural soils are the source of 75% of anthropogenic N 2 O emissions globally. Recently, significant attention has been directed at examining effects of conservation tillage on carbon sequestration in agricultural systems. However, limited knowledge is available regarding how these practices impact N 2 O emissions, especially for organic vegetable production systems. In this context, a three-year study was conducted in a well-drained sandy loam field transitioning to organic vegetable production in the Mid-Atlantic coastal plain of USA to investigate impacts of conservation tillage [strip till (ST) and no-till (NT)] and conventional tillage (CT) [with black plastic mulch (CT-BP) and bare-ground (CT-BG)] on N 2 O emissions. Each year, a winter cover crop mixture (forage radish: Raphanus sativus var. longipinnatus, crimson clover: Trifolium incarnatum L., and rye: Secale cereale L.) was grown and flail-mowed in the spring. Nearly 80% of annual N 2 O-nitrogen (N) emissions occurred during the vegetable growing season for all treatments. Annual N 2 O-N emissions were greater in CT-BP than in ST and NT, and greater in CT-BG than in NT, but not different between CT-BG and CT-BP, ST and NT, or CT-BG and ST. Conventional tillage promoted N mineralization and plastic mulch increased soil temperature, which contributed to greater N 2 O-N fluxes. Though water filled porosity in NT was higher and correlated well with N 2 O-N fluxes, annual N 2 O-N emissions were lowest in NT suggesting a lack of substrates for nitrification and denitrification processes. Crop yield was lowest in NT in Year 1 and CT-BP in Year 3 but yield-scaled N 2 O-N emissions were consistently greatest in CT-BP and lowest in NT each year. Our results suggest that for coarse-textured soils in the coastal plain with winter cover crops, conservation tillage practices may reduce N 2 O emissions in organic vegetable production systems. [ABSTRACT FROM AUTHOR]

Nitrate (NO 3 − ) leaching and nitrous oxide (N 2 O) emission from urine patches in grazed pastures are key sources of water and air pollution, respectively. Broadcast spraying of the nitrification inhibitor dicyandiamide (DCD) has been shown to reduce these losses, but it is expensive. As an alternative, it had been demonstrated that feeding DCD to cattle (after manual mixing with supplementary feeds) was a practical, effective and cheaper method to deliver high DCD rates within urine patches. This two-year study carried out on simulated urine patches in three application seasons (spring, summer, autumn) explored the efficacy of DCD feeding to cattle to reduce N losses from grazed pasture soil in a heavy-textured soil under temperate climatic conditions. In each application season, DCD fed to cows, then excreted with urine and applied at a rate of 30 kg DCD ha − 1 (treatment U + DCD 30 -f) was as effective as powdered DCD mixed with normal urine and applied at the same rate (treatment U + DCD 30 ) at reducing cumulative N 2 O-N emissions and the N 2 O-N emission factor (EF3, expressed as % of N applied). Increasing DCD loading within urine patches from 10 to 30 kg DCD ha − 1 improved efficacy by significantly reducing the EF3 from 34% to 64%, which highlights that under local conditions, 10 kg DCD ha − 1 (the recommended rate for commercial use in New Zealand) was not the optimum DCD rate to curb N 2 O emissions. The modelling of EF3 in this study also suggests that N mitigation should be given more attention when soil moisture is going to be high, which can be predicted with short-term weather forecasting. DCD feeding, for instance in autumn when cows are not lactating and the risk of N losses is high, could then be reduced by focusing mainly on those forecasted wet periods. [ABSTRACT FROM AUTHOR]

Denitrification characteristics of forest soils from eight headwater catchments in China were investigated in this study, along a climatic gradient from the tropics in the South to the temperate zones. Within each catchment, different landscape positions along hydrological flow paths were also considered, including well-drained soils on hill slopes and poorly drained soils in groundwater discharge zones. The results showed that instantaneous denitrification rates were much greater in soils from the northern sites than those from the southern sites (with the average of 110.0 and 25.4 nmol N g −1 dry soil h. − 1 , respectively). Large potentials for nitrous oxide (N 2 O) loss (evaluated as maximum N 2 O accumulation before it was reduced to dinitrogen (N 2 )) were observed in the six tropical and subtropical catchments, particularly in soils with high carbon (C) and nitrogen (N). Meanwhile high N 2 O / (N 2 O + N 2 ) stoichiometries were displayed in soils from these southern sites. Within catchments, soils from the groundwater discharge zones showed greater potential denitrification rates but smaller N 2 O / (N 2 O + N 2 ) ratios in comparison with those on the hill slopes, implying large N removal potentials of soils from the groundwater discharge zones. Furthermore, our findings suggest soil pH is the key controller for the potential denitrification rates and the N 2 O / (N 2 O + N 2 ) stoichiometries. Soil pH, C and N availability affect the potential for N 2 O loss synergistically. Our findings not only pinpoint the denitrification phenotypes of soils along the climatic gradient, but also confirm the small-scale variations within catchments which reflect the in situ habitat of the denitrifiers. These indicate the importance of discrimination related to different landscape positions when modeling N 2 O emissions and N removals from regional N loading. [ABSTRACT FROM AUTHOR]

Grazed pastures are a major contributor to emissions of the greenhouse gas nitrous oxide (N 2 O), and urine deposition from grazing animals is the main source of the emissions. Incorporating alternative forages into grazing systems could be an approach for reducing N 2 O emissions through mechanisms such as release of biological nitrification inhibitors from roots and increased root depth. Field plot and lysimeter (intact soil column) trials were conducted in a free draining Horotiu silt loam soil to test whether two alternative forage species, plantain ( Plantago lanceolate L.) and lucerne ( Medicago sativa L.), could reduce N 2 O emissions relative to traditional pasture species, white clover ( Trifolium repens L.) and perennial ryegrass ( Lolium perenne L.). The amounts of N 2 O emitted from the soil below each forage species, which all received the same cow urine at the same rates, was measured using an established static chamber method. Total N 2 O emissions from the plantain, lucerne and perennial ryegrass controls (without urine application) were generally very low, but emissions from the white clover control were significantly higher. When urine was applied in autumn or winter N 2 O emissions from plantain were lower compared with those from perennial ryegrass or white clover, but this difference was not found when urine was applied in summer. Lucerne had lower emissions in winter but not in other seasons. Incorporation of plantain into grazed pasture could be an approach to reduce N 2 O emissions. However, further work is required to understand the mechanisms for the reduced emissions and the effects of environmental conditions in different seasons. [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]

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]

The availability of detailed input data frequently limits the application of process-based models at large scale. In this study, we produced simplified meta-models of the simulated nitrous oxide (N 2 O) emission factors (EF) using NZ-DNDC. Monte Carlo simulations were performed and the results investigated using multiple regression analysis to produce simplified meta-models of EF. These meta-models were then used to estimate direct N 2 O emissions from grazed pastures in New Zealand. New Zealand EF maps were generated using the meta-models with data from national scale soil maps. Direct emissions of N 2 O from grazed pasture were calculated by multiplying the EF map with a nitrogen (N) input map. Three meta-models were considered. Model 1 included only the soil organic carbon in the top 30 cm (SOC30), Model 2 also included a clay content factor, and Model 3 added the interaction between SOC30 and clay. The median annual national direct N 2 O emissions from grazed pastures estimated using each model (assuming model errors were purely random) were: 9.6 Gg N (Model 1), 13.6 Gg N (Model 2), and 11.9 Gg N (Model 3). These values corresponded to an average EF of 0.53%, 0.75% and 0.63% respectively, while the corresponding average EF using New Zealand national inventory values was 0.67%. If the model error can be assumed to be independent for each pixel then the 95% confidence interval for the N 2 O emissions was of the order of ± 0.4–0.7%, which is much lower than existing methods. However, spatial correlations in the model errors could invalidate this assumption. Under the extreme assumption that the model error for each pixel was identical the 95% confidence interval was approximately ± 100–200%. Therefore further work is needed to assess the degree of spatial correlation in the model errors. [ABSTRACT FROM AUTHOR]

Dung and urine excreted onto grasslands are a major source of nitrous oxide (N 2 O). These N 2 O emissions stem from inefficient utilisation of nitrogen (N) ingested by ruminants, and the inability of pasture to utilise the deposited N. Predicted growth in dairy and meat consumption means that there is a requirement to quantify N 2 O emissions, and investigate emission reduction mechanisms. Three 12 month ‘seasonal’ experiments were undertaken at Crichton, SW Scotland, where N 2 O emissions were measured from applications of cattle urine, dung, artificial urine and urine + a nitrification inhibitor (NI), dicyandiamide (DCD). The three application timings were ‘spring’, ‘summer’ and ‘autumn’, representative of early-, mid- and late grazing seasons. N 2 O emissions were measured from static chambers for 12 months. The aim was to quantify emissions from cattle excreta, and determine their dependence on the season of application, and the respective contribution of dung and urine to total excreta emissions. Measurement from NI amended urine was made to assess DCD's potential as an emission mitigation tool. Emissions were compared to the IPCC's default emission factor (EF) of 2% for cattle excreted N. Mean annual cumulative emissions from urine were the highest when applied in summer (5034 g N 2 O-N ha − 1 ), with lower emissions from spring (1903 g N 2 O-N ha − 1 ) and autumn (2014 g N 2 O-N ha − 1 ) application, most likely due to higher temperatures and soil moisture conducive to both nitrification and denitrification in the summer months. Calculated EFs were significantly greater from urine (1.1%) than dung (0.2%) when excreta was applied in summer, and EFs varied with season of application, but in all experiments were lower than the IPCC default of 2%. These results support both lowering and disaggregating this EF into individual EFs for dung and urine. Addition of DCD to urine caused no significant reduction in emissions, suggesting that more research is required into its use as a mitigation option. [ABSTRACT FROM AUTHOR]

In this study, methane (CH4) and nitrous oxide (N2O) emission dynamics of a plug-flow bioreactor located in a municipal full-scale wastewater treatment plant were monitored during a period of 10 weeks. In general, CH4 and N2O gas emissions from the bioreactor accounted for 0.016% of the influent chemical oxygen demand (COD) and 0.116% of the influent total Kjeldahl nitrogen (TKN) respectively. In order to identify the emission patterns in the different zones, the bioreactor was divided in six different sampling sites and the gas collection hood was placed for a period of 2-3 days in each of these sites. This sampling strategy also allowed the identification of different process perturbations leading to CH4 or N2O peak emissions. CH4 emissions mainly occurred in the first aerated site, and were mostly related with the influent and reject wastewater flows entering the bioreactor. On the other hand, N2O emissions were given along all the aerated parts of the bioreactor and were strongly dependant on the occurrence of process disturbances such as periods of no aeration or nitrification instability. Dissolved CH4 and N2O concentrations were monitored in the bioreactor and in other parts of the plant, as a contribution for the better understanding of the transport of these greenhouse gases across the different stages of the treatment system. [ABSTRACT FROM AUTHOR]

It is anticipated that organic farming systems provide benefits concerning soil conservation and climate protection. A literature search on measured soil-derived greenhouse gas (GHG) (nitrous oxide and methane) fluxes under organic and non-organic management from farming system comparisons was conducted and followed by a meta-analysis. Up to date only 19 studies based on field measurements could be retrieved. Based on 12 studies that cover annual measurements, it appeared with a high significance that area-scaled nitrous oxide emissions from organically managed soils are 492±160kg CO2 eq. ha−1 a−1 lower than from non-organically managed soils. For arable soils the difference amounts to 497±162kg CO2 eq. ha−1 a−1. However, yield-scaled nitrous oxide emissions are higher by 41±34kg CO2 eq. t−1 DM under organic management (arable and use). To equalize this mean difference in yield-scaled nitrous oxide emissions between both farming systems, the yield gap has to be less than 17%. Emissions from conventionally managed soils seemed to be influenced mainly by total N inputs, whereas for organically managed soils other variables such as soil characteristics seemed to be more important. This can be explained by the higher bioavailability of the synthetic N fertilisers in non-organic farming systems while the necessary mineralisation of the N sources under organic management leads to lower and retarded availability. Furthermore, a higher methane uptake of 3.2±2.5kg CO2 eq. ha−1 a−1 for arable soils under organic management can be observed. Only one comparative study on rice paddies has been published up to date. All 19 retrieved studies were conducted in the Northern hemisphere under temperate climate. Further GHG flux measurements in farming system comparisons are required to confirm the results and close the existing knowledge gaps. [ABSTRACT FROM AUTHOR]

Abstract: Nitrous oxide (N2O) is a primary ozone-depleting substance and powerful greenhouse gas. N2O emissions from secondary-level wastewater treatment processes are relatively well understood as a result of intensive international research effort in recent times, yet little information exists to date on the role of sewers in wastewater management chain N2O dynamics. Here we provide the first detailed assessment of N2O levels in the untreated influent (i.e. sewer network effluent) of three large Australian metropolitan wastewater treatment plants. Contrary to current international (IPCC) guidance, results show gravity sewers to be a likely source of N2O. Results from the monitoring program revealed hydraulic flow rate as a strong driver for N2O generation in gravity sewers, with microbial processes (nitrification and possibly denitrification) implicated as the main processes responsible for its production. Results were also used to develop a presumptive emission factor for N2O in the context of municipal gravity sewers. Considering the discrepancy with current IPCC Guidelines, further work is warranted to assess the scale and dynamics of N2O production in sewers elsewhere. [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]

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 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]