Field scale N2O flux measurements from grassland using eddy covariance

In order to assess nitrous oxide (N₂O) emissions from typical intensively managed grassland in northern Britain fluxes were measured by eddy covariance using tuneable diode laser absorption spectroscopy from June 2002 to June 2003 for a total period of 4000 h. With micrometeorological techniques it is possible to obtain a very detailed picture of the fluxes of N₂O at field scale (10³–10⁴ m²), which are valuable for extrapolation to regional scales. In this paper three of the four fertilizer applications were investigated in detail. N₂O emissions did not always show a clear response. Hourly fluxes were very large immediately after the June 2002 nitrogen fertilizer application, peaking at 2.5 mg N₂O–N m^–2 s^–1. Daily fluxes were averaging about 300 ng N₂O m^–2 s^–1 over the 4 days following fertilizer application. The response of N₂O emissions was less evident after the August fertilization, although 2 days after fertilizer application an hourly maximum flux of 554 ng N₂O–N m^–2 s^–1 was registered. For the rest of August the flux was undetectable. The differences between fertilization events can be explained by different environmental conditions, such as soil temperature and rainfall. A fertiliser-induced N₂O emission was not observed after fertilizer application in March 2003, due to lack of rainfall. The total N₂O flux from June 2002 to June 2003 was 5.5 kg N₂O–N ha^–1y^–1, which is 2.8% of the total annual N fertilizer input.     

Winter and Spring Thaw Measurements of N2O,NO and NOx Fluxes using a Micrometeorological Method

The impact of nitrogen fertilizers on gaseous emissions duringwinter and spring-thaw is not well understood and was the objective of this research. Using a micrometeorological method,N₂O, NO and NO_x fluxes from ryegrass were measured from November 1997 to March 1998. Three different mineralfertilizers were applied in November: urea (U), slow-release urea(SRU) and ammonium nitrate (AN). N₂O emissions during the winter were small, increasing significantly in March. Total losses of N₂O-N were significantly higher from SRU and U plots, with winter N₂O emissions accounting for 50% of annual losses. Nitric oxide fluxes from all plots weresmall during the measurement period (<0.9 ng N m^-2 s^-1). The NO fluxes from U and AN fertilized plots were significantly higher than from SRU and control plots. NO₂ fluxes were always negative (–6 ng N m^-2 s^-1)indicating deposition, but decreased to –2 ng N m^-2s^-1 when snow was present on the soil surface. Our resultsindicate that the form of inorganic N applied has an effect on NO+ N₂O emissions but not on NO₂ fluxes.Sponsored by CAPES – Brasília, Brazil     

Measuring eddy covariance fluxes of ammonia using tunable diode laser absorption spectroscopy

Field measurements of NH₃ fluxes using an eddy covariance technique were made for a total of 60 days between July and September 2002 at an intensively managed grassland in Southern Scotland. The collected data demonstrate the suitability of a tuneable diode laser absorption spectroscopy (TDLAS) system coupled with a sonic anemometer for eddy covariance measurements. The novelty of these measurements is the application to ammonia, which has only become measurable using TDLAS techniques recently, because of its small ambient concentration. Data presented in this paper show typical features of the fluxes and concentration for the summer season. NH₃ concentration and flux values are in a similar range to previous studies using flux gradient methods at the same field site, although the particularly wet season reduced the concentration of NH₃ in the air. For an example day, measured NH₃ fluxes ranged between ?11 and 44 ng m^?2 s^?1 with an average value of 3.78 ng m^?2 s^?1 indicating a small net emission from the vegetation. Spectral analysis executed on the data shows the percentage of flux carried by the small eddies (from 0.2 to 2 m) suggesting that high detection frequency instruments are particularly suitable for estimating NH₃ fluxes between atmosphere and vegetation.     

Greenhouse gas emissions from landfill leachate treatment plants: A comparison of young and aged landfill

With limited assessment, leachate treatment of a specified landfill is considered to be a significant source of greenhouse gas (GHG) emissions. In our study, the cumulative GHG emitted from the storage ponds and process configurations that manage fresh or aged landfill leachate were investigated. Our results showed that strong CH₄ emissions were observed from the fresh leachate storage pond, with the fluxes values (2219–26,489 mg C m^?2 h^?1) extremely higher than those of N₂O (0.028–0.41 mg N m^?2 h^?1). In contrast, the emission values for both CH₄ and N₂O were low for the aged leachate tank. N₂O emissions became dominant once the leachate entered the treatment plants of both systems, accounting for 8–12% of the removal of N-species gases. Per capita, the N₂O emission based on both leachate treatment systems was estimated to be 7.99 g N₂O–N capita^?1 yr^?1. An increase of 80% in N₂O emissions was observed when the bioreactor pH decreased by approximately 1 pH unit. The vast majority of carbon was removed in the form of CO₂, with a small portion as CH₄ (<0.3%) during both treatment processes. The cumulative GHG emissions for fresh leachate storage ponds, fresh leachate treatment system and aged leachate treatment system were 19.10, 10.62 and 3.63 Gg CO₂ eq yr^?1, respectively, for a total that could be transformed to 9.09 kg CO₂ eq capita^?1 yr^?1.     

Nitrous oxide emission from some English and Welsh rivers and estuaries

Nutrient and N₂O concentrations in the water columns were measured seasonally over a full salinity range in the nutrified rivers Colne, Stour, Orwell, Deben, Trent, Ouse and Humber and their estuaries on the east coast of England between August 2001 and May 2002, and in the oligotrophic rivers Conwy, Dovey and Mawddach in North and West Wales between August 2002 and May 2003. Nutrient and N₂O concentrations in the nutrified English rivers and estuaries were much higher than those in the Welsh rivers. N₂O concentrations and % saturation in the estuaries were significantly correlated with nitrate, nitrite and ammonium concentrations in the water. The strongest correlation was with nitrite (r ² = 0.56, p < 0.01), suggesting that nitrite was the most significant factor among the different nutrients in regulating N₂O concentration in the estuaries. N₂O concentrations in the English rivers and estuaries were supersaturated throughout the year with annual averages from 186.9 to 992.9%, indicating that these rivers and estuaries were sources of atmospheric N₂O, whereas in the Welsh rivers N₂O concentrations were much lower with annual averages from 113.6 to 137.4% saturation. Although the estuarine area in the Colne was almost the same as that in the Conwy, the annual N₂O emission from the Colne was much higher (937498 mol N yr^?1) than in the Conwy (23020 mol N yr^?1). On the east coast, riverine emissions of N₂O were only 0.5–12.5% of the total emission from rivers and estuaries. Thus rivers were negligible, but estuaries were significant contributors to the UK N₂O inventory.     

The influence of atmospheric n deposition on nitrous oxide and nitric oxide fluxes and soil ammonium and nitrate concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO^? ₃ and NH⁺ ₄ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH⁺ ₄ and NO^? ₃ concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH⁺ ₄and NO^? ₃ in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH⁺ ₄, but the relationship between NH⁺ ₄ and N deposition (ln NH⁺ ₄ = 0.62 ln N_deposition+0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Spatial variability of nitrous oxide and methane emissions from an MBT landfill in operation: Strong N2O hotspots at the working face

Mechanical biological treatment (MBT) is an effective technique, which removes organic carbon from municipal solid waste (MSW) prior to deposition. Thereby, methane (CH₄) production in the landfill is strongly mitigated. However, direct measurements of greenhouse gas emissions from full-scale MBT landfills have not been conducted so far. Thus, CH₄ and nitrous oxide (N₂O) emissions from a German MBT landfill in operation as well as their concentrations in the landfill gas (LFG) were measured. High N₂O emissions of 20–200 g CO₂ eq. m^?2 h^?1 magnitude (up to 428 mg N m^?2 h^?1) were observed within 20 m of the working face. CH₄ emissions were highest at the landfill zone located at a distance of 30–40 m from the working face, where they reached about 10 g CO₂ eq. m^?2 h^?1. The MBT material in this area has been deposited several weeks earlier. Maximum LFG concentration for N₂O was 24.000 ppmv in material below the emission hotspot. At a depth of 50 cm from the landfill surface a strong negative correlation between N₂O and CH₄ concentrations was observed. From this and from the distribution pattern of extractable ammonium, nitrite, and nitrate it has been concluded that strong N₂O production is associated with nitrification activity and the occurrence of nitrite and nitrate, which is initiated by oxygen input during waste deposition. Therefore, CH₄ mitigation measures, which often employ aeration, could result in a net increase of GHG emissions due to increased N₂O emissions, especially at MBT landfills.     

Measuring Eddy Covariance Fluxes of Ammonia Using Tunable Diode Laser Absorption Spectroscopy

Field measurements of NH3 fluxes using an eddy covariance technique were made for a total of 60 days between July and September 2002 at an intensively managed grassland in Southern Scotland. The collected data demonstrate the suitability of a tuneable diode laser absorption spectroscopy (TDLAS) system coupled with a sonic anemometer for eddy covariance measurements. The novelty of these measurements is the application to ammonia, which has only become measurable using TDLAS techniques recently, because of its small ambient concentration. Data presented in this paper show typical features of the fluxes and concentration for the summer season. NH3 concentration and flux values are in a similar range to previous studies using flux gradient methods at the same field site, although the particularly wet season reduced the concentration of NH₃ in the air. For an example day, measured NH₃ fluxes ranged between –11 and 44 ng m^–2 s^–1 with an average value of 3.78 ng m^–2 s^–1 indicating a small net emission from the vegetation. Spectral analysis executed on the data shows the percentage of flux carried by the small eddies (from 0.2 to 2 m) suggesting that high detection frequency instruments are particularly suitable for estimating NH₃ fluxes between atmosphere and vegetation.     

A Relaxed Eddy Accumulation System for the Automated Measurement of Atmospheric Ammonia Fluxes

A continuous relaxed eddy accumulation system ispresented for the automated measurement of surface/atmosphere exchange fluxes of atmospheric ammonia (NH₃) at a single height. The new system features sampling by parallel plate denuder inlets, online chemical analysis using the conductivity cell of a commercially available NH₃ analyzer and online flux calculation. The effective detection limit of the system for air concentrations is 0.2 g m^-3 and it is estimated to resolve fluxes > ± 20 ng m^-2 s^-1, depending on the NH₃ concentration and turbulence. The performance of the system was tested in two measurement campaigns above agricultural grassland, in which it was compared with a 3-point continuous gradient system. During the first campaign, after urea application of 47 kg N ha^-1 in autumn, the REA system derived fluxes which were on average twice as large as the gradient fluxes, while concentrations agreed closely (on average within 4%). Possible reasons include differences in the footprint and an over-correction of the gradient flux in stable conditions. Due to wet and cold conditions, only 0.3% of the fertilizer N was volatilized as NH₃ during the first week. Results from the deployment of an improved system are presented for a summer day, 6 days after fertilization with calcium ammonium nitrate. The agreement of both concentrations (on average within 13%) and fluxes (26%) was very encouraging and similar to the agreement found between two state-of-the-art gradient systems with online analysis.     

Nitrous Oxide Emissions from Two Riparian Ecosystems: Key Controlling Variables

Nitrous oxide (N₂O) emissions were measured weekly to fortnightly between April 2001 and March 2002 from two riparian ecosystems drainingdifferent agricultural fields. The fields differed in the nature of the crop grown and the amount of fertiliser applied. Soil water content and soil temperature were very important controls of N₂O emission rates, with a ‘threshold’ response at 24% moisture content (by volume) and 8 °C, below which N₂O emission was very low.N₂O fluxes were higher at the site that had receivedthe most fertiliser N, but NO₃ ^- was not a limiting factor at either site. There was also a ‘threshold’ effect of rainfall, in which major rainfall events (≥10 mm) triggered a pulse of high N₂O emission if none of the other environmental factors were limiting. These results suggest the existence of multiple controls on N₂O emissions operating at a range of spatial and temporal scales and that non-linear relationships, perhaps with a hierarchical structure, are needed to model these emissions from riparian ecosystems.     

Feasibility of greenhouse gas emissions offsets for natural source zone depletion of petroleum hydrocarbons

Hydrocarbon biodegradation is an important process for remediating petroleum hydrocarbons and managing large sites. However, this biodegradation results in what are essentially unavoidable CO₂ emissions to the atmosphere. A feasibility assessment was conducted to quantitatively consider reuse options for petroleum brownfields that would offset contaminant respiration emissions rates in the 2 to 10 micromoles CO₂ per meters squared per second (μmol CO₂ m^?2 s^?1) typically observed. Under a wide range of solar resource scenarios, placement of solar panels over only a fraction (no more than 35%) of the site footprint is estimated as necessary to achieve an emissions offset. Similarly, placement of one 30‐meter tall wind turbine of moderate rating (approximately 30 to 50 kW) is sufficient to provide an offset for a nominal 1,000 square meters site. For spreading of spent calcium‐rich construction materials, under even a high emissions scenario, the required footprint for the offset is less than the site footprint. While these approaches appear feasible, revegetation as forestland is estimated as sufficient only at contaminant respiration rates up to 2 μmol CO₂ m^?2 s^?1. Revegetation as rangeland and cropland, which sequesters CO₂ mainly in soil organic carbon, is estimated as requiring more than the site footprint under many contaminant respiration rates. Revegetation as a wetland fares slightly better from a carbon storage perspective, but it also has the potential for N₂O and CH₄ emissions that may largely undo the benefit from sequestration in soil organic matter. Overall, the results indicate several methods that are viable for achieving emissions offsets and a quantitation method that can be honed with site‐specific input parameters as appropriate.     

The release of nitrous oxide from the intertidal zones of two European estuaries in response to increased ammonium and nitrate loading

Nitrous oxide (N₂O) release and denitrification rates were investigated from the intertidal saltmarsh and mudflats of two European river estuaries, the Couesnon in Normandy, France and the Torridge in Devon, UK. Sediment cores and water were collected from each study site and incubated for 72 h in tidal simulation chambers. Gas samples were collected at 6 and 12 h intervals from the chambers during incubation. From these N₂O emission rates were calculated. The greatest rates for both N₂O production and denitrification were measured from saltmarsh cores. These were 1032 μmol N₂O m^?2 day^?1 and 2518 μmol N₂ m^?2 day^?1, respectively, from the Couesnon and 109 μmol N₂O m^?2 day^?1 and 303 μmol N₂ m^?2 day^?1 from the Torridge. A strong positive correlation was apparent with N₂O emission rates and ammonium concentration in the sediment, nitrate concentration in floodwater and sediment aerobicity.     

Nitrous oxide emission from some English and Welsh rivers and estuaries

Nutrient and N₂O concentrations in the water columns were measured seasonally over a full salinity range in the nutrified rivers Colne, Stour, Orwell, Deben, Trent, Ouse and Humber and their estuaries on the east coast of England between August 2001 and May 2002, and in the oligotrophic rivers Conwy, Dovey and Mawddach in North and West Wales between August 2002 and May 2003. Nutrient and N₂O concentrations in the nutrified English rivers and estuaries were much higher than those in the Welsh rivers. N₂O concentrations and % saturation in the estuaries were significantly correlated with nitrate, nitrite and ammonium concentrations in the water. The strongest correlation was with nitrite (r² = 0.56, p < 0.01), suggesting that nitrite was the most significant factor among the different nutrients in regulating N₂O concentration in the estuaries. N₂O concentrations in the English rivers and estuaries were supersaturated throughout the year with annual averages from 186.9 to 992.9%, indicating that these rivers and estuaries were sources of atmospheric N₂O, whereas in the Welsh rivers N₂O concentrations were much lower with annual averages from 113.6 to 137.4% saturation. Although the estuarine area in the Colne was almost the same as that in the Conwy, the annual N₂O emission from the Colne was much higher (937498 mol N yr^–1) than in the Conwy (23020 mol N yr^–1). On the east coast, riverine emissions of N₂O were only 0.5–12.5% of the total emission from rivers and estuaries. Thus rivers were negligible, but estuaries were significant contributors to the UK N₂O inventory.     

Effect of fresh green waste and green waste compost on mineral nitrogen, nitrous oxide and carbon dioxide from a Vertisol

Incorporation of organic waste amendments to a horticultural soil, prior to expected risk periods, could immobilise mineral N, ultimately reducing nitrogen (N) losses as nitrous oxide (N₂O) and leaching. Two organic waste amendments were selected, a fresh green waste (FGW) and green waste compost (GWC) as they had suitable biochemical attributes to initiate N immobilisation into the microbial biomass and organic N forms. These characteristics include a high C:N ratio (FGW 44:1, GWC 35:1), low total N (<1%), and high lignin content (>14%). Both products were applied at 3 t C/ha to a high N (plus N fertiliser) or low N (no fertiliser addition) Vertisol soil in PVC columns. Cumulative N₂O production over the 28 day incubation from the control soil was 1.5 mg/N₂O/m², and 11 mg/N₂O/m² from the control + N. The N₂O emission decreased with GWC addition (P < 0.05) for the high N soil, reducing cumulative N₂O emissions by 38% by the conclusion of the incubation. Analysis of mineral N concentrations at 7, 14 and 28 days identified that both FGW and GWC induced microbial immobilisation of N in the first 7 days of incubation regardless of whether the soil environment was initially high or low in N; with the FGW immobilising up to 30% of available N. It is likely that the reduced mineral N due to N immobilisation led to a reduced substrate for N₂O production during the first week of the trial, when soil N₂O emissions peaked. An additional finding was that FGW + N did not decrease cumulative N₂O emissions compared to the control + N, potentially due to the fact that it stimulated microbial respiration resulting in anaerobic micro sites in the soil and ultimately N₂O production via denitrification. Therefore, both materials could be used as post harvest amendments in horticulture to minimise N loss through nitrate-N leaching in the risk periods between crop rotations. The mature GWC has potential to reduce N₂O, an important greenhouse gas.     

Quantifying dry NH3 deposition to an ombrotrophic bog from an automated NH3 field release system

Providing an accurate estimate of the dry component of N deposition to low N background, semi-natural habitats, such as bogs and upland moors dominated by Calluna vulgaris is difficult, but essential to relate nitrogen deposition to effects in these communities. To quantify the effects of NH₃ inputs to moorland vegetation growing on a bog at a field scale, a field release NH₃ fumigation system was established at Whim Moss (Scottish Borders) in 2002. Gaseous NH₃ from a line source was released along of a 60 m transect, when meteorological conditions (wind speed >2.5 m s^?1 and wind direction in the sector 180–215°) were met, thereby providing a profile of decreasing NH₃ concentration with distance from the source. In a complementary study, using a NH₃ flux chamber system, the relationships between NH₃ concentrations and cuticular resistances were quantified for a range of NH₃ concentrations and micrometeorological conditions for moorland vegetation. Cuticular resistances increased with NH₃ concentration from 11 s m^?1 at 3.0 μg m^?3 to 30 s m^?1 at 30 μg m^?3. The NH₃ concentration data and the concentration-dependent canopy resistance are used to calculate NH₃ deposition taking into account leaf surface wetness. The implications of using an NH₃ concentration-dependent cuticular resistance and the importance for refining critical loads are discussed.     

The Influence of Atmospheric N Deposition on Nitrous Oxide and Nitric Oxide Fluxes and Soil Ammonium and Nitrate Concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO ₃ ^– and NH ₄ ⁺ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH ₄ ⁺ and NO ₃ ^– concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH ₄ ⁺ and NO ₃ ^– in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH ₄ ⁺ , but the relationship between NH ₄ ⁺ and N deposition (ln NH ₄ ⁺ = 0.62 ln N_deposition + 0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Greenhouse gas emissions from home composting of organic household waste

The emission of greenhouse gases (GHGs) is a potential environmental disadvantage of home composting. Because of a lack of reliable GHG emission data, a comprehensive experimental home composting system was set up. The system consisted of six composting units, and a static flux chamber method was used to measure and quantify the GHG emissions for one year composting of organic household waste (OHW). The average OHW input in the six composting units was 2.6–3.5 kg week^?1 and the temperature inside the composting units was in all cases only a few degrees (2–10 °C) higher than the ambient temperature. The emissions of methane (CH₄) and nitrous oxide (N₂O) were quantified as 0.4–4.2 kg CH₄ Mg^?1 input wet waste (ww) and 0.30–0.55 kg N₂O Mg^?1 ww, depending on the mixing frequency. This corresponds to emission factors (EFs) (including only CH₄ and N₂O emissions) of 100–239 kg CO₂-eq. Mg^?1 ww. Composting units exposed to weekly mixing had the highest EFs, whereas the units with no mixing during the entire year had the lowest emissions. In addition to the higher emission from the frequently mixed units, there was also an instant release of CH₄ during mixing which was estimated to 8–12% of the total CH₄ emissions. Experiments with higher loads of OHW (up to 20 kg every fortnight) entailed a higher emission and significantly increased overall EFs (in kg substance per Mg^?1 ww). However, the temperature development did not change significantly. The GHG emissions (in kg CO₂-eq. Mg^?1 ww) from home composting of OHW were found to be in the same order of magnitude as for centralised composting plants.     

Methane oxidation at a surface-sealed boreal landfill

Methane oxidation was studied at a closed boreal landfill (area 3.9 ha, amount of deposited waste 200,000 tonnes) equipped with a passive gas collection and distribution system and a methane oxidative top soil cover integrated in a European Union landfill directive-compliant, multilayer final cover. Gas wells and distribution pipes with valves were installed to direct landfill gas through the water impermeable layer into the top soil cover. Mean methane emissions at the 25 measuring points at four measurement times (October 2005–June 2006) were 0.86–6.2 m³ ha^?1 h^?1. Conservative estimates indicated that at least 25% of the methane flux entering the soil cover at the measuring points was oxidized in October and February, and at least 46% in June. At each measurement time, 1–3 points showed significantly higher methane fluxes into the soil cover (20–135 m³ ha^?1 h^?1) and methane emissions (6–135 m³ ha^?1 h^?1) compared to the other points (<20 m³ ha^?1 h^?1 and <10 m³ ha^?1 h^?1, respectively). These points of methane overload had a high impact on the mean methane oxidation at the measuring points, resulting in zero mean oxidation at one measurement time (November). However, it was found that by adjusting the valves in the gas distribution pipes the occurrence of methane overload can be to some extent moderated which may increase methane oxidation. Overall, the investigated landfill gas treatment concept may be a feasible option for reducing methane emissions at landfills where a water impermeable cover system is used.     

Impact of nitrate-enhanced leachate recirculation on gaseous releases from a landfill bioreactor cell

This study evaluates the impact of nitrate injection on a full scale landfill bioreactor through the monitoring of gaseous releases and particularly N₂O emissions. During several weeks, we monitored gas concentrations in the landfill gas collection system as well as surface gas releases with a series of seven static chambers. These devices were directly connected to a gas chromatograph coupled to a flame ionisation detector and an electron capture detector (GC-FID/ECD) placed directly on the field. Measurements were performed before, during and after recirculation of raw leachate and nitrate-enhanced leachate. Raw leachate recirculation did not have a significant effect on the biogas concentrations (CO₂, CH₄ and N₂O) in the gas extraction network. However, nitrate-enhanced leachate recirculation induced a marked increase of the N₂O concentrations in the gas collected from the recirculation trench (100-fold increase from 0.2 ppm to 23 ppm). In the common gas collection system however, this N₂O increase was no more detectable because of dilution by gas coming from other cells or ambient air intrusion. Surface releases through the temporary cover were characterized by a large spatial and temporal variability. One automated chamber gave limited standard errors over each experimental period for N₂O releases: 8.1 ± 0.16 mg m^?2 d^?1 (n = 384), 4.2 ± 0.14 mg m^?2 d^?1 (n = 132) and 1.9 ± 0.10 mg m^?2 d^?1 (n = 49), during, after raw leachate and nitrate-enhanced leachate recirculation, respectively. No clear correlation between N₂O gaseous surface releases and recirculation events were evidenced. Estimated N₂O fluxes remained in the lower range of what is reported in the literature for landfill covers, even after nitrate injection.     

Spatially Disaggregated Inventories of Soil NO and N2O Emissions for Great Britain

Estimates of soil N₂O and NOemissions at regional and country scales arehighly uncertain, because the most widely usedmethodologies are based on few data, they do notinclude all sources and do not account forspatial and seasonal variability. To improveunderstanding of the spatial distribution of soilNO and N₂O emissions we have developedsimple multi-linear regression models based onpublished field studies from temperate climates.The models were applied to create spatialinventories at the 5 km² scale of soil NOand N₂O emissions for Great Britain. The N₂O regression model described soilN₂O emissions as a function of soil N input,soil water content, soil temperature and land useand provided an annual N₂O emission of 128 kt N₂O-N yr^-1. Emission rates largerthan 12 kg N₂O-N ha^-1 yr^-1 werecalculated for the high rainfall grassland areasin the west of Great Britain.Soil NO emissions were calculated using tworegression models, which described NO emissionsas a function of soil N input with and without afunction for the water filled pore space. Thetotal annual emissions from both methods, 66 and7 kt NO-N yr^-1, respectively, span the rangeof previous estimates for Great Britain.