Significant N2O Emissions Research Articles

Assessing nitrous oxide emissions from algal-bacterial photobioreactors devoted to biogas upgrading and digestate treatment

Nitrous oxide (N2O) emissions in High Rate Algal Ponds (HRAP) can negatively affect the sustainability of algal-bacterial processes. N2O emissions from a pilot HRAP devoted to biogas upgrading and digestate treatment were herein monitored for 73 days. The influence of the pH (7.5, 8.5, and 9.5), nitrogen sources (100 mg L−1 of N–NO2-, N–NO3-, and N–NH4+) and illumination on N2O emissions from the algal-bacterial biomass of the HRAP was also assessed in batch tests. Significantly higher N2O gas concentrations of 311.8 ± 101.1 ppmv were recorded in the dark compared to the illuminated period (236.9 ± 82.6 ppmv) in the HRAP. The batch tests revealed that the highest N2O emission rates (49.4 mmol g−1 TSS·h−1) occurred at pH 8.5 in the presence of 100 mg N–NO2-/L under dark conditions. This study revealed significant N2O emissions in HRAPs during darkness.

Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg−1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Competitive partitioning of denitrification pathways during arrested methanogenesis: Implications in ammonium recovery, N2O emission, and volatile fatty acid production

The complex interaction between nitrate (NO3−) reduction and fermentation is poorly understood when high levels of NO3− are introduced into anaerobic systems. This study investigated the competitive distribution between conventional denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA) during simultaneous denitrification and fermentation in arrested methanogenesis. Up to 62% of initial NO3− (200 mg-N/L) was retained as ammonium through DNRA at a chemical oxygen demand (COD)/N ratio of 25. Significant N2O emission occurred (1.7 – 8.0% of the initial NO3−) with limited carbon supply (≤1600 mg COD/L) and sludge concentration (≤3000 mg COD/L). VFA composition shifted predominantly towards acetic acid (>50%) in the presence of nitrate. A novel kinetic model was developed to predict DNRA vs. DEN partitioning and NO2− accumulation. Overall, NO3− input, organic loading, and carbon source characteristics independently and collectively controlled competitive DNRA vs. DEN partitioning.

Potential Risk of Significant N2O Emission without Changing NOx Conversion on Commercial V2O5/TiO2 Catalyst under Working Conditions.

Vanadium-based catalysts play a pivotal role in the emission control of industrial NOx via selective catalytic reduction (SCR) technology. However, little attention has been paid to the potential emission of greenhouse gas N2O under complex working conditions. This work reports that a commercial V2O5/TiO2 catalyst may lead to significant N2O emission without greatly changing the outlet NOx concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N2O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N2O/(N2O+N2) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N2O formation in a wide temperature range of 250 ∼ 400 °C. It is stemmed from the fact that the covalent interaction between Cr and V species on the V2O5/TiO2 surface accelerates the conversion of V4+ + Cr6+ → V5+ + Cr3+, leading to a larger proportion of surface V5+. More importantly, surface V5+ is highly related to the redox property of the V2O5/TiO2 catalyst, which is beneficial to NSCR reaction rather than the standard SCR process. The work suggests that to better inhibit the emission of greenhouse gases during the NH3-SCR process, monitoring N2O emission should be included along with the NOx concentrations, especially in complex flue gases.

Transient nitrite accumulation explains the variation of N2O emissions to N fertilization in upland agricultural soils

Nitrogen (N) fertilization in agricultural soils is the largest anthropogenic source of nitrous oxide (N2O) emissions, but the underlying mechanism of the varied response of N2O emissions to N fertilizer is unclear. We investigated the response of N2O emissions to ammonium-based fertilizers and nitrification inhibitors in upland agricultural soils across northern China. Large variations in N2O emissions in different upland soils in response to N fertilization were found, whereas the variations were well correlated with soil nitrite (NO2−) dynamics (P < 0.01). A higher pH soil is generally correlated with a higher potential nitrification and denitrification rate, a higher AOB/AOA gene abundance ratio, higher NO2− content, and higher N2O emission. The efficacy of 3,4-dimethylpyrazole phosphate (DMPP) for inhibiting net nitrification increased with increasing soil pH. Further investigation showed that rapid ammonia oxidation drives oxygen (O2) depletion and NO2− accumulation in the soil matrix, which stimulates N2O emission and inhibits N2 emission under anoxic conditions. Collectively, our results showed that alkaline soils tend to have rapid ammonia oxidation potential, leading to transient NO2− accumulation and O2 depletion in the soil matrix after large ammonium addition. This might trigger significant N2O emissions from denitrification and DNRA, which explains the spatial heterogeneity of N2O emissions in response to N fertilization in various upland soils.

Effect of aeration modes on nitrogen removal and N2O emission in the partial nitrification and denitrification process for landfill leachate treatment

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 N2O 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 N2O emission. DO concentration higher than 1.5 mg/L in the aerobic phase reduced nitrogen removal and led to a significant high N2O emission in the process. Complete nitrite denitrification in the anoxic phase correlated with minimized N2O emission. Under efficient nitrogen removal stage, N2O 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.

Emission factors for Vietnamese beef cattle manure sun-drying and the effects of drying on manure microbial community.

Livestock manure and its management are significant sources of greenhouse gas (GHG). In most Southeast Asian countries, the current GHG emissions are estimated by the Intergovernmental Panel on Climate Change (IPCC) Tier 1 approach using default emission factors. Sun-drying is the dominant manure treatment in Vietnam, and in this study, we measured GHG emissions during manure drying using a chamber-based approach. Results show the emission factors for CH4 and N2O were 0.295 ± 0.078 g kg-1 volatile solids (VS) and 0.132 ± 0.136 g N2O-N kg-1 Ninitial, respectively. We monitored the total bacterial/archaeal community using 16S rRNA gene amplicon sequencing and measured the abundance of functional genes required for methanogenesis (mcrA), nitrification (amoA) and denitrification (nirK, nirS and nosZ) processes. Methane emission occurred only at the beginning of the drying process (days 1 to 3). The results of amplicon sequencing indicated that the relative abundance of methanogens also decreased during this period. Although some nitrification activity was detected, there was no significant N2O emission. These findings well describe the manure management system in south Vietnam and the GHG emission from this manure category, paving the way for higher Tier estimations using country-specific values.

Influence of Azolla incorporation and/or dual cropping on CH4 and N2O emission from a paddy field

ABSTRACT Our previous pot experiments showed that using Azolla either or both as dual and green manure with rice increases its yield or significantly reduces either or both methane (CH4) and nitrous oxide (N2O) emissions. To confirm these findings in an actual field, Azolla was either grown as a dual crop (herein Cover) or incorporated as green manure plus dual cropping (herein AGM + Cover) at the beginning of the experiment along with rice. Compared with the control (chemical fertilizer; herein NPK), NPK + Cover and AGM + Cover treatments did not influence cumulative CH4 emissions throughout the rice growth period. However, AGM + Cover treatment affected significant CH4 emissions at early, middle, and later rice growth stages by 140.6%, 24.6%, and 33.1%, respectively, compared with NPK + Cover treatment. These emissions were attributed to the readily available carbon substrate for methanogens following the incorporation of Azolla as green manure. Compared with NPK, NPK + Cover and AGM + Cover significantly increased N2O emissions by 645.9% and 816.2%, respectively, during the middle rice growth stage. No significant N2O emission differences were observed in the three treatments in the early or later rice growth stages. The higher N2O emissions from the middle rice growth stage were ascribed to high substrate availability from the dead Azolla by higher summer air temperature in the 2019 season. AGM + Cover significantly decreased rice yield by 37.5% (NPK) and 35.3% (NPK + Cover), with no significant differences between NPK and NPK + Cover. This reduction was attributed to nitrogen immobilization from the incorporated Azolla during the early stage. Therefore, to ascertain the potential of Azolla in paddy fields to address environmental safety while sustaining yield, emphasis on the interaction of different application methods with various management practices is necessary.

The Effect of Cutting and Waterlogging on Plant-Related CO2 and N2O Fluxes Associated with the Invasive N-Fixing Species Gunnera tinctoria

The overall impact that plant invasions have on greenhouse gas emissions (GHG) by plant-mediated effects and how these interact with environmental and management factors is largely unknown. To address this, we report on the effects of leaf removal and waterlogging, either singularly or in combination, on the fluxes of CO2 and N2O associated with the invasive species Gunnera tinctoria. Both the removal of leaves with and without flooding resulted in higher CO2 emissions due to reductions in photosynthesis. Whilst waterlogging alone was also associated with a reduction in photosynthesis, this was slower than the effect of leaf removal. Significant N2O emissions were associated with intact plants, which increased immediately after leaf removal, or seven days after waterlogging with or without leaf removal. We found positive correlations between CO2 and N2O emissions and petiole and rhizome areas, indicating a size-dependent effect. Our results demonstrate that intact plants of G. tinctoria are a source of N2O emissions, which is enhanced, albeit transiently, by the removal of leaves. Consequently, management interventions on invasive plant populations that involve the removal of above-ground material, or waterlogging, would not only reduce CO2 uptake, but would further compromise the ecosystem GHG balance through enhanced N2O emissions.

Ammonia-oxidizing archaea are integral to nitrogen cycling in a highly fertile agricultural soil

Nitrification is a central process in the global nitrogen cycle, carried out by a complex network of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), complete ammonia-oxidizing (comammox) bacteria, and nitrite-oxidizing bacteria (NOB). Nitrification is responsible for significant nitrogen leaching and N2O emissions and thought to impede plant nitrogen use efficiency in agricultural systems. However, the actual contribution of each nitrifier group to net rates and N2O emissions remain poorly understood. We hypothesized that highly fertile agricultural soils with high organic matter mineralization rates could allow a detailed characterization of N cycling in these soils. Using a combination of molecular and activity measurements, we show that in a mixed AOA, AOB, and comammox community, AOA outnumbered low diversity assemblages of AOB and comammox 50- to 430-fold, and strongly dominated net nitrification activities with low N2O yields between 0.18 and 0.41 ng N2O–N per µg NOx–N in cropped, fallow, as well as native soil. Nitrification rates were not significantly different in plant-covered and fallow plots. Mass balance calculations indicated that plants relied heavily on nitrate, and not ammonium as primary nitrogen source in these soils. Together, these results imply AOA as integral part of the nitrogen cycle in a highly fertile agricultural soil.

Distinctive Patterns and Controls of Nitrous Oxide Concentrations and Fluxes from Urban Inland Waters.

Inland waters are significant sources of nitrous oxide (N2O), a powerful greenhouse gas. However, considerable uncertainty exists in the estimates of N2O efflux from global inland waters due to a lack of direct measurements in urban inland waters, which are generally characterized by high carbon and nitrogen concentrations and low carbon-to-nitrogen ratios. Herein, we present direct measurements of N2O concentrations and fluxes in lakes and rivers of Beijing, China, during 2018-2020. N2O concentrations and fluxes in the waters of Beijing exceeded previous estimates of global rivers due to the high carbon and nutrient concentrations and high aquatic productivity. In contrast, the N2O emission factor (N2O-N/DIN, median 0.0005) was lower than global medians and the N2O yield (ΔN2O/(ΔN2O + ΔN2), average 1.6%) was higher than those typically observed in rivers and streams. The positive relationship between N2O emissions and denitrifying bacteria as well as the Michaelis-Menten relationship between N2O emissions and NO3--N concentrations suggested that bacteria control the net production of N2O in waters of Beijing with N saturation, leading to a low N2O emission factor. However, low carbon-to-nitrogen ratios are beneficial for N2O accumulation during denitrification, resulting in high N2O yields. This study demonstrates the significant N2O emissions and their distinctive patterns and controls in urban inland waters and suggests that N2O emission estimates based on nitrogen loads and simple emission factor values are not appropriate for urban inland water systems.

Spatial and temporal variability of soil N2 O and CH4 fluxes along a degradation gradient in a palm swamp peat forest in the Peruvian Amazon.

Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is extensively threatened by degradation. The unsustainable practice of cutting whole palms for fruit extraction modifies forest's structure and composition and eventually alters peat‐derived greenhouse gas (GHG) emissions. We evaluated the spatiotemporal variability of soil N2O and CH4 fluxes and environmental controls along a palm swamp degradation gradient formed by one undegraded site (Intact), one moderately degraded site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis considered structural changes in vegetation and soil microtopography as impacted by degradation. Variables were monitored monthly over 3 years to evaluate intra‐ and inter‐annual variability. Degradation induced microscale changes in N2O and CH4 emission trends and controls. Site‐scale average annual CH4 emissions were similar along the degradation gradient (225.6 ± 50.7, 160.5 ± 65.9 and 169.4 ± 20.7 kg C ha−1 year−1 at the Intact, mDeg and hDeg sites, respectively). Site‐scale average annual N2O emissions (kg N ha−1 year−1) were lower at the mDeg site (0.5 ± 0.1) than at the Intact (1.3 ± 0.6) and hDeg sites (1.1 ± 0.4), but the difference seemed linked to heterogeneous fluctuations in soil water‐filled pore space (WFPS) along the forest complex rather than to degradation. Monthly and annual emissions were mainly controlled by variations in WFPS, water table level (WT) and net nitrification for N2O; WT, air temperature and net nitrification for CH4. Site‐scale N2O emissions remained steady over years, whereas CH4 emissions rose exponentially with increased precipitation. While the minor impact of degradation on palm swamp peatland N2O and CH4 fluxes should be tested elsewhere, the evidenced large and variable CH4 emissions and significant N2O emissions call for improved modeling of GHG dynamics in tropical peatlands to test their response to climate changes.

Co-application of poultry-litter biochar with Azolla has synergistic effects on CH4 and N2O emissions from rice paddy soils

Poultry-litter biochar and Azolla as green manure amendments are reported to enhance paddy soil fertility and rice yields. However, whether their co-application in lowland rice paddies has synergistic effects and whether those benefits are accompanied by greenhouse gas (GHG) emissions remains unknown. The objective of this study was to determine the effects of poultry-litter biochar (hereafter: biochar) and its co-application with Azolla as green manure (hereafter: Azolla), on the simultaneous methane (CH4) and nitrous oxide (N2O) emissions from a lowland paddy soil planted with rice during a single rice growing season in Tsuruoka, Yamagata, Japan. Biochar and Azolla amendments were applied once before rice was transplanted at a density of 20 t ha−1 and 133.9 kg N ha−1, respectively. Compared with NPK, NPK + biochar, and Azolla only treatments, Azolla and biochar co-application (i.e., Azolla + biochar) significantly increased CH4 emissions by 33%–197.6% in the early stages of rice growth (before 63 days after transplanting, DAT), but did not significantly influence CH4 emissions at both late rice growth stages (after 63 DAT,) and whole rice growth period (112 DAT). Conversely, Azolla + biochar significantly reduced N2O emissions by 83.0%–97.1% before 63 DAT, and by 76.4%–95.9% during the whole rice growth period at 112 DAT, with a significantly high interaction between biochar and fertilizer amendments. There were no significant N2O emission differences among all treatments after 63 DAT. Additionally, Azolla + biochar significantly increased rice grain yield by 27.3%–75.0%, and consequently, decreased both yield-equivalent CH4 emissions by 24.7%–25.0% and N2O emissions by 81.8%–97.7%. Our findings suggest that the co-application of poultry-litter biochar and Azolla as green manure offers a novel approach to increase rice yield while reducing the emissions of non-carbon dioxide greenhouse gases.

Increased nitrous oxide emissions from intertidal soil receiving wastewater from dredging shrimp pond sediments

The quantities of greenhouse gas emissions and the activity of functional microbes in coastal soils receiving nutrient-rich wastewaters from mariculture activities have seldom been reported. We investigated the effects of wastewater discharge resulting from dredging shrimp pond sediment on the soil fluxes of methane (CH4) and nitrous oxide (N2O) in intertidal areas and on the functional microorganisms and physio-chemical characteristics of soil. The temporal variations in gas fluxes and soil characteristics following wastewater discharge were also evaluated with the tidal regime on the day of discharge taken into account. The results showed that wastewater discharge immediately resulted in higher levels of ammonia (NH4+-N) deposited and N2O emissions from the soil at the discharge site than at the non-discharge site, while the CH4 flux was not affected. The increase in N2O flux lasted for a longer time when the discharge was performed during a neap tide day than when it was performed during a spring tide day. Wastewater discharge also increased the abundance of ammonia-oxidizing bacterial (AOB) amoA genes and nosZ genes in soil rather than increasing the abundance of narG and nirK genes. The pattern of temporal variations between the N2O flux and soil NH4+–N content was similar to that between the flux and the AOB-amoA gene abundance, suggesting that bacterial nitrification was important for N2O production in soil receiving the dredging wastewater. The results suggest that the wastewater discharge impacts nitrogen metabolism processes and causes a significant N2O emission problem; therefore, pollutant management is essential in shrimp culturing activities to reduce greenhouse gas emissions into the atmosphere.

Nitrous oxide emissions during microalgae-based wastewater treatment: current state of the art and implication for greenhouse gases budgeting.

Microalgae can synthesise the ozone depleting pollutant and greenhouse gas nitrous oxide (N2O). Consequently, significant N2O emissions have been recorded during real wastewater treatment in high rate algal ponds (HRAPs). While data scarcity and variability prevent meaningful assessment, the magnitude reported (0.13-0.57% of the influent nitrogen load) is within the range reported by the Intergovernmental Panel on Climate Change (IPCC) for direct N2O emissions during centralised aerobic wastewater treatment (0.016-4.5% of the influent nitrogen load). Critically, the ability of microalgae to synthesise N2O challenges the IPCC's broad view that bacterial denitrification and nitrification are the only major cause of N2O emissions from wastewater plants and aquatic environments receiving nitrogen from wastewater effluents. Significant N2O emissions have indeed been repeatedly detected from eutrophic water bodies and wastewater discharge contributes to eutrophication via the release of nitrogen and phosphorus. Considering the complex interplays between nitrogen and phosphorus supply, microalgal growth, and microalgal N2O synthesis, further research must urgently seek to better quantify N2O emissions from microalgae-based wastewater systems and eutrophic ecosystems receiving wastewater. This future research will ultimately improve the prediction of N2O emissions from wastewater treatment in national inventories and may therefore affect the prioritisation of mitigation strategies.

Significant N2O emission from a high rate granular reactor for completely autotrophic nitrogen removal over nitrite

Expanded granular sludge bed (EGSB) reactors were rarely applied for complete ammonium removal over nitrite. In this study, a high ammonium loading rate of 3677 mg N/L/d was achieved in an EGSB reactor. Approximately 5.5–8.5% of influent ammonium was converted to nitrous oxide (N2O) that is a potent greenhouse gas. Moreover, the percentage increased linearly with the increase in ammonium load. A model well matched the reactor dynamics. The model indicated that hydroxylamine (NH2OH) oxidation contributed to over 40% of produced N2O, and denitrification by ammonium oxidizing bacteria contributed to N2O emission significantly. Furthermore, the model suggests that a low oxygen concentration can result in a low N2O emission at the cost of a slightly low ammonium removal rate while influent organic matter play a minor role in reducing N2O emission. This study shows that EGSB reactors are effective in ammonium removal. In addition, the emission of N2O is significant.

Scenario analysis on abating industrial process greenhouse gas emissions from adipic acid production in China

Adipic acid is an important petrochemical product, and its production process emits a high concentration of greenhouse gas N2O. This paper aims to provide quantitative references for relevant authorities to formulate greenhouse gas control roadmaps. The forecasting method of this paper is consistent with the published national inventory in terms of caliber. Based on the N2O abatement technical parameters of adipic acid and the production trend, this paper combines the scenario analysis and provides a measurement of comprehensive N2O abatement effect of the entire industry in China. Four future scenarios are assumed. The baseline scenario (BAUS) is a frozen scenario. Three emission abatement scenarios (ANAS, SNAS, and ENAS) are assumed under different strength of abatement driving parameters. The results show that China’s adipic acid production process can achieve increasingly significant N2O emission abatement effects. Compared to the baseline scenario, by 2030, the N2O emission abatements of the three emission abatement scenarios can reach 207–399 kt and the emission abatement ratios can reach 32.5%–62.6%. By 2050, the N2O emission abatements for the three emission abatement scenarios can reach 387–540 kt and the emission abatement ratios can reach 71.4%–99.6%.

Duration and frequency of drainage and flooding events interactively affect soil biogeochemistry and N flux in subtropical peat soils

With the demand for restoration and future prediction of climate change effects, subtropical peatlands are expected to be subjected to hydrologic regimes with variable duration and frequency of drained and flooded conditions, but knowledge of their interactive effects on soil biogeochemistry and emission of greenhouse gases including nitrous oxide (N2O) is largely limited. The objective of this study was to investigate how the duration and frequency of drainage and flooding events interactively influence soil biogeochemical properties and denitrification and related net N2O production rates following rewetting. Surface soils are susceptible to different hydrologic regimes. Significantly higher pH, extractable organic carbon (ext. OC), ammonium (NH4+-N), denitrification enzyme activity (DEA), but lower nitrate (NO3−-N), microbial biomass C and N were observed when the peat soils were under flooded conditions compared to drained conditions. Two-week and four-week drainage or flooding duration did not result in statistically significant differences in soil biogeochemical properties. A 24-week prolonged drainage led to an accumulation of NO3−-N and a significantly lower pH. Soil microbial biomass and fungal:bacterial abundance likely increased with the frequency of drainage-flooding cycles. Significant differences in denitrification and net N2O production rates following reflooding were mainly found in the surface soils. Structural equation modeling indicated that hydroperiod and water-filled pore space (WFPS) prior to reflooding is likely to control denitrification and net N2O production through its regulation of NO3−-N and activity of microorganisms involved in denitrification while higher drainage-flooding frequency decreases the availability of organic C and NO3−-N for denitrification. Our results also suggest high NO3−-N and low pH within peat soils caused by prolonged drainage likely leads to a significant N2O emission pulse following reflooding. For peat soils subjected to frequent drainage-flooding cycles, N2O emission pulses following reflooding would decrease with time, attributing to the loss of substrates for denitrification.

Effects of Packaging and Food Waste Prevention by Consumers on the Environmental Impact of Production and Consumption of Bread in Norway

Bread is a staple food in Norway, with a yearly per capita consumption of 52 kg. It is an important source of energy, dietary fibre and protein as well as certain minerals and vitamins. Previous studies have shown that bread has a relatively low environmental impact compared with other foods. Food waste studies, however, have shown that bread and other baked goods have a high wastage rate in Norway. On the basis of lower Norwegian wheat yields, it is therefore expected that the environmental impact of bread could be higher than in other European countries. The purpose of this study was to assess the environmental impact of bread from cradle to grave, identify environmental hotspots, examine the role of packaging in bread waste and identify possible remediation measures with a particular focus on the post-farm value chain. The results showed that for every kilogram of bread consumed, the global warming potential was 0.99 kg CO2-eq, the eutrophication potential was 7.2 g PO4-eq, the acidification potential was 8.4 g SO2-eq and the cumulative energy demand was 18 MJ. The principal uncertainty within the calculation was the use of database data for the 21 ingredients. For example, the effect of soil mineralisation, which could give significant CO2 and N2O emissions, was not included because figures have only been quantified for a few ingredients and there is no international agreement on the methodology. The primary hotspot was the production of the ingredients, principally at the agricultural stage, while bread waste took the second place. The highest potential for the reduction of post-farm environmental impact lies in reducing product wastage at the retail and consumer stages. Consumers already employ strategies to reduce wastage, such as using extra packaging and freezing and toasting bread. This study shows that other consumer packaging solutions can keep the bread fresh for longer, thus reducing wastage and the need for the abovementioned consumer strategies. Nevertheless, other researches in this subject have shown that consumer preferences and behaviours play a significant role in the creation of bread waste, and this should therefore be taken into account when planning reduction measures.

Nitrous oxide emissions could reduce the blue carbon value of marshes on eutrophic estuaries

The supply of nitrogen to ecosystems has surpassed the Earth’s Planetary Boundary and its input to the marine environment has caused estuarine waters to become eutrophic. Excessive supply of nitrogen to salt marshes has been associated with shifts in species’ distribution and production, as well as marsh degradation and loss. Our study of salt marshes in agriculturally intensive watersheds shows that coastal eutrophication can have an additional impact. We measured gas fluxes from marsh soils and verified emissions of nitrous oxide (N2O) in nitrogen-loaded marshes while the reference marsh was a sink for this gas. Salt marsh soils are extremely efficient carbon sinks, but emissions of N2O, a greenhouse gas 298 times more potent than CO2, reduces the value of the carbon sink, and in some marshes, may counterbalance any value of stored carbon towards mitigation of climate change. Although more research is merited on the nitrogen transformations and carbon storage in eutrophic marshes, the possibility of significant N2O emissions should be considered when evaluating the market value of carbon in salt marshes subject to high levels of nitrogen loading.