Flux Chamber Research Articles

Comprehensive effects of a sedge plant on CH4 and N2O emissions in an estuarine marsh

Although there have been numerous studies focusing on plants' roles in methane (CH4) emissions, the influencing mechanism of wetland plants on nitrous oxide (N2O) emissions has rarely been studied. Here, we test whether wetland plants also play an important role in N2O emissions. Gas fluxes were determined using the in situ static flux chamber technique. We also carried out pore-water extractions, sedge removal experiments and tests of N2O transportation. The brackish marsh acted as a net source of both CH4 and N2O. However, sedge plants played the opposite role in CH4 and N2O emissions. The removal of the sedges led to reduced CH4 emissions and increased accumulation of CH4 inside the sediment. Apart from being a conduit for CH4 transport, the sedges made a greater contribution to CH4 oxidation than CH4 production. The sedges exerted inhibitory effects on the release of N2O. The N2O was barely detectable inside the sediment in both vegetated and vegetation-removed plots. The denitrification measurements and nitrogen addition (the addition rates were equal to 0.028, 0.056 and 0.112 g m−2) experiments suggest that denitrification associated with N2O production occurred mainly in the surface sediment layer. The vascular sedge could transport atmospheric N2O downward into the rhizosphere. The rhizospheric sediment, together with the vascular sedge, became an effective sink of atmospheric N2O.

Measurement of methane emissions from abandoned oil and gas wells in Hillman State Park, Pennsylvania

ABSTRACTAbandoned oil and gas wells, improperly plugged or unplugged, present a risk to current and future oil and gas development because they provide a potential pathway for unwanted gas and fluid migration to the surface. The appropriate emission factor for gaseous emissions from these wells is uncertain, as a limited number of studies have reported abandoned wells as a methane emissions source. A helicopter-based survey that mapped methane concentration and located wells by detecting magnetic anomalies was conducted in Hillman State Park in southwestern Pennsylvania. Although well finding via aerial survey was successful, elevated methane concentrations due to emissions from wells in the survey area were not detected by helicopter as abandoned wells were likely too small a source of methane to detect from elevations that helicopters fly at (tens of meters). Measurement of methane emission rates from 31 wells were collected using several techniques that are compared and evaluated for their effectiveness: Hi Flow sampler, field-portable flame ionization detector, infrared camera, dynamic flux chamber and bag sampling. Nine of the 31 wells were buried; average methane flux for these wells was not statistically different from the background. Mass flow rate from the remaining 22 wells ranged from non-detection (less than 0.09 kg CH4/day) to 4.18 kg CH4/day with a mean of 0.70 kg/well/day (median of 0.24 kg CH4/day/well) and a sample standard of error of 0.21 kg CH4/well/day. This emission factor, while not intended for exclusive use in developing a methane emissions inventory for abandoned oil and gas wells, contributes to the growing amount of methane emissions data for this source category. The results from the aerial survey, ground-based well location verification and emissions measurements, and the evaluation of measurement approaches described here, provide a comprehensive characterization of abandoned wells in one field that can inform future measurement studies.

Quantifying greenhouse gas emissions from municipal solid waste dumpsites in Cameroon

Open dumpsites that receive municipal solid waste are potentially significant sources of greenhouse gas (GHG) emissions into the atmosphere. There is little data available on emissions from these sources, especially in the unique climate and management of central Africa. This research aimed at quantifying CH4, N2O and CO2 emissions from two open dumpsites in Cameroon, located in Mussaka-Buea, regional headquarters of the South West Region and in Mbellewa-Bamenda, regional headquarters of the North West Region. Emissions were measured during the wet season (May 2015 and August 2016) at the Mussaka and Mbellewa dumpsites respectively. Dumpsite surfaces were partitioned into several zones for emission measurements, based on the current activity and the age of the waste. Static flux chambers were used to quantify gas emission rates thrice a day (mornings, afternoons and evenings). Average emissions were 96.80 ± 144 mg CH4 m−2 min−1, 0.20 ± 0.43 mg N2O m−2 min−1 and 224.78 ± 312 mg CO2 m−2 min−1 in the Mussaka dumpsite, and 213.44 ± 419 mg CH4 m−2 min−1, 0.15 ± 0.15 mg N2O m−2 min−1 and 1103.82 ± 1194 mg CO2 m−2 min−1 at the Mbellewa dumpsite. Emissions as high as 1784 mg CH4 m−2 min−1, 2.3 mg N2O m−2 min−1 and 5448 mg CO2 m−2 min−1 were measured from both dumpsites. Huge variations observed in emissions between the different zones on the waste surface were likely a result of the heterogeneous nature of the waste, different stages in waste decomposition and different environmental conditions within the waste. Management activities that disturb waste, such as spreading and compressing potentially increase gas emissions, while covering waste with a layer of soil potentially mitigate gas emissions. Recommendations were for dumpsites to be upgraded to sanitary landfills, and biogas production from such landfills should be exploited to reduce CH4 emissions.

Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

Abstract. Freshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO2) and methane (CH4) to the atmosphere. Global estimates of freshwater emissions traditionally use a wind-speed-based gas transfer velocity, kCC (introduced by Cole and Caraco, 1998), for calculating diffusive flux with the boundary layer method (BLM). We compared CH4 and CO2 fluxes from BLM with kCC and two other gas transfer velocities (kTE and kHE), which include the effects of water-side cooling to the gas transfer besides shear-induced turbulence, with simultaneous eddy covariance (EC) and floating chamber (FC) fluxes during a 16-day measurement campaign in September 2014 at Lake Kuivajärvi in Finland. The measurements included both lake stratification and water column mixing periods. Results show that BLM fluxes were mainly lower than EC, with the more recent model kTE giving the best fit with EC fluxes, whereas FC measurements resulted in higher fluxes than simultaneous EC measurements. We highly recommend using up-to-date gas transfer models, instead of kCC, for better flux estimates. BLM CO2 flux measurements had clear differences between daytime and night-time fluxes with all gas transfer models during both stratified and mixing periods, whereas EC measurements did not show a diurnal behaviour in CO2 flux. CH4 flux had higher values in daytime than night-time during lake mixing period according to EC measurements, with highest fluxes detected just before sunset. In addition, we found clear differences in daytime and night-time concentration difference between the air and surface water for both CH4 and CO2. This might lead to biased flux estimates, if only daytime values are used in BLM upscaling and flux measurements in general. FC measurements did not detect spatial variation in either CH4 or CO2 flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH4 fluxes but did show a clear difference between CO2 fluxes from shallower and deeper areas. We highlight that while all flux measurement methods have their pros and cons, it is important to carefully think about the chosen method and measurement interval, as well as their effects on the resulting flux.

Passive diffusive flux chambers - a new method to quantify vapour intrusion into indoor air.

A new instrumental method (a passive flux chamber) to quantify emission rates of volatile organic compounds (VOCs) from natural ground surfaces and floors or pavements was developed and tested against the traditional emission isolation flux chamber (the dynamic flux chamber). Dynamic flux chambers have been used for some decades to measure diffusive mass flux of VOCs at contaminated sites thereby providing quantitative estimates of the contribution of contaminant vapour fluxes to indoor air concentrations for human health risk assessments. The new method described here measures diffusive mass flux from surfaces utilising a high uptake rate passive absorptive sampling tube placed within a chamber to capture the mass molecular flux. The passive flux chamber was developed to provide a technically simpler and more cost effective means of quantifying vapour intrusion rates into buildings where the dominant pathway for VOC intrusion through floors is molecular diffusion rather than pressure driven advective flows through floor gaps and cracks. The passive flux chamber operation is based on the principal of molecular diffusion and the random movement of molecules in the gaseous phase. The efficiency of the passive chamber in capturing the total mass flux was tested by measuring comparative concentrations in adjacent identical chambers, one fitted with and the other without an absorptive sampling tube. For chambers fitted with sampling tubes the internal chamber concentrations of VOCs were on average 85% lower than for co-located chambers not fitted with the absorption tubes, demonstrating a high rate of capture of VOC flux into the chamber and a close and satisfactory approximation of mass flux. Eighteen field comparisons of surface fluxes measured by the passive and dynamic flux chamber methods showed that on average the passive chambers produced flux rates a factor of two greater than the dynamic flux chambers.

Ammonia Volatilization from Putting Greens Foliarly Fertilized by Conventional or Stabilized Urea

Core Ideas Specific circumstances may limit use of all existing turfgrass best management practices. Urea fertilizer amended by biological inhibitors was foliarly applied to turfgrass. Flux chambers were used to measure NH3 volatilization over 24 hours. Addition of NBPT+DCD to aqueous urea significantly inhibited NH3 volatilization. Commercial or on‐site NBPT+DCD amendment of urea reduced NH3‐N loss by 6.5 to 7.3%. Low cost, high N content, and favorable handling characteristics of urea fertilizer (46–0–0) make its use common in turfgrass management. While many investigations confirm incomplete recovery of foliarly applied urea‐N by turfgrass putting greens, the efficacy of urease‐inhibiting additives, calcium‐maleic‐itaconic polymer or N‐(n‐butyl) thiophosphoric triamide (NBPT), in preventing NH3 volatilization is currently undocumented. Furthermore, NH3 emissions reduce air and water quality. From 2014 to 2015, NH3 volatilization was measured 0 to 24 h following foliar application of conventional or stabilized urea fertilizers to ‘Penn G2’ creeping bentgrass (Agrostis stolonifera L.) putting greens at a 20 kg ha−1 N rate in four separate trials. Using a 63% trapping‐efficiency flux chamber system under the duration and conditions described, 11.1% of conventional or calcium‐maleic‐itaconic polymer–amended urea‐N was lost as NH3. Alternatively, combined amendment by NBPT and dicyandiamide (DCD) prevented 1.3 to 1.4 kg ha−1 NH3–N emissions, reducing volatilization loss to only 3.8 to 4.6% of the foliarly applied urea‐N.

Evaluation of a Simple, Small-Plot Meteorological Technique for Measurement of Ammonia Emission: Feasibility, Costs, and Recommendations

Abstract. Ammonia emission reduces the reliability and nitrogen (N) fertilizer efficiency of animal manure and mineral fertilizers applied to fields. The loss of ammonia to the atmosphere is frequently compensated for by costly over-application of N fertilizers. New technologies to reduce ammonia emission are regularly developed, and their efficacy needs to be tested using accurate methods. To date, a major obstacle to many available emission measurement techniques is the requirement of large plot sizes of homogeneous surface characteristics, which particularly is a challenge to the number of plot-level replicates that can be carried out on a field providing uniform surface characteristics throughout. The objectives of this research were to test three different methods for measuring NH3 flux when applied to small plots (<315 m2) by comparison with conventional micrometeorological methods and to determine the labor intensity and expenses related to the respective methods in their entirety. The integrated horizontal flux (IHF) method and the ZINST method were used with passive flux Leuning samplers as micrometeorological reference methods. As examples of conventional small-plot emission measurement techniques, wind tunnels measuring gas-phase ammonia using ALPHA passive diffusion samplers and a flux chamber method using Dräger tubes for measurements of ammonia concentration (DTM) were used. As an inexpensive alternative small-plot method, we studied the feasibility of applying ALPHA passive diffusion samplers and battery-driven cup anemometers at ZINST height on small source areas (<315 m2), coupled with a backward Lagrangian stochastic (bLS) dispersion model to calculate emission fluxes (referred to as the AbLS method). When exposure duration was appropriate and weather conditions were not extreme, tests showed no significant difference in NH3 emission fluxes measured with AbLS, compared to those obtained with IHF and ZINST using Leuning samplers. However, the AbLS method did not give reliable emission measurements in periods with high wind speeds and heavy rain. It was also shown that the AbLS method provided valid results when reducing the plot radius from the standard 20 m to 10 m, or even 5 m, provided that the ALPHA samplers were exposed for at least 5 or 6 h. Emission from 200 kg urea-N ha-1 was between 20 and 30 kg N ha-1 in the two trials. The cost for one study running for one week using the ZINST or bLS methodology, including equipment for four plots and eight measurement intervals, was $2785 if horizontal fluxes were measured using the ALPHA samplers, compared to $12,301 using the Leuning samplers and $13,928 using gas washing bottles. Using the DTM flux chamber method once is a little more expensive than using the AbLS method, but less expensive if the cost of purchasing the equipment is distributed over five studies in five years. Using wind tunnels is as costly as measuring emissions with the Leuning samplers or gas washing bottles using the bLS or ZINST method. Keywords: ALPHA samplers, Ammonia emission, AbLS, bLS method, DTM method, IHF method, Labor cost, Passive ammonia samplers, Wind tunnels.

Greenhouse Gas Emissions from Beef Feedlot Surface Materials as Affected by Diet, Moisture, Temperature, and Time

Abstract. A laboratory study was conducted to measure the effects of diet, moisture, temperature, and time on greenhouse gas (GHG) emissions from feedlot surface materials (FSM). The FSM were collected from open-lot pens where beef cattle were fed either a dry-rolled corn (DRC) diet containing no wet distillers grains with solubles (WDGS) or a DRC diet containing 35% WDGS. The FSM were collected, air-dried or mixed with 3.0 L of water to represent dry or wet conditions, and then incubated at temperatures of 5°C, 15°C, 25°C, or 35°C. Static flux chambers were used to quantify GHG emissions over a 14-day period. Flux data for each diet × moisture combination were analyzed using repeated measures in time. The largest GHG emissions occurred under wet conditions at temperatures of 25°C and 35°C. Flux values for these conditions typically were significantly greater than measurements obtained on the same day at 5°C and 15°C. Mean emissions under wet conditions for CO2, CH4, and N2O were 35, 121, and 278 times greater, respectively, than emissions from dry FSM. The 0% WDGS diet produced mean CO2 and N2O flux measurements that were 1.8 and 1.5 times greater, respectively, than those obtained for the 35% WDGS diet. The 35% WDGS diet, in contrast, produced a mean CH4 emission rate that was 6 times greater than the 0% WDGS diet. Management for GHG mitigation should include design and/or maintenance of pen drainage to speed drying as well as the use of modified animal diets. Keywords: Air quality, Carbon dioxide, Confined animal feeding operations, Drainage, Emission rates, Feedlot, Greenhouse gas, Methane, Nitrous oxide, Pen design.

Comparison of direct benthic flux to ebullition-facilitated flux of polycyclic aromatic hydrocarbons and heavy metals measured in the field

No studies to date have compared directly the ebullition-facilitated organic and metal contaminant fluxes to direct benthic contaminant fluxes measured in the field. To address this knowledge gap, we measured benthic organic and metal contaminant fluxes at the sediment-water interface and compared them to simultaneously measured ebullition-facilitated contaminant fluxes at nine sites in a contaminated waterway in the Chicago River, IL, USA, to determine the relative importance of each transport mechanism to total sediment release. Two benthic flux chambers with integrated gas ebullition samplers were built to measure both gas ebullition and in situ fluxes of polycyclic aromatic hydrocarbons (PAHs), metals, sulfide, ammonia, nitrate, dissolved organic carbon (DOC), total filtered phosphorus (TFP), and dissolved oxygen (DO) across the sediment-water interface over time. Aqueous pH and oxidation-reduction potential (ORP) within the chamber were also monitored. The gas ebullition collection system trapped heavy metals and the 16 United States Environmental Protection Agency (USEPA) priority-pollutant PAHs (Σ16PAH) transported with gas bubbles through sorption and particle entrainment on a pre-combusted glass wool trap as in our previous studies. The results demonstrate that gas ebullition contaminant transport is a significant source of pollution release to the water column, as great as or greater than direct benthic transport. In several sites, release rates of Σ16PAHs and some metals from the sediment by gas ebullition were more than an order of magnitude higher than from direct benthic release. The average total PAH ebullition-facilitated release of all sites is predicted to be nearly 0.5 g m−2 on an annual basis. Gas ebullition is an important pathway for release of PAHs and heavy metal pollutants to the water column and monitoring of this important release pathway should be performed to adequately address the true environmental impacts of polluted sediments.

Emission factors of greenhouse gases from layer and broiler barns in Cameroon

Limited information is available in the literature on greenhouse gas (GHG) quantification from livestock production systems in Africa. Therefore, this project was carried out to generate baseline emission factors of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) from broiler and layer barns with building design typical of Cameroon. Emissions were measured from two broiler barns during the entire production cycles and a layer barn for a limited period using flux chambers. Methane emission factors from the broiler barns with mud and cement floors were 0.96 ± 1.04 and 0.36 ± 0.17 mg bird−1 hr−1 respectively, and 0.76 ± 0.56 mg bird−1 hr−1 from the layer barn with cement floor. Nitrous oxide emission from the broiler barns with mud and cement floors were 12.94 ± 10.11 and 1.68 ± 1.02 mg bird−1 hr−1 respectively, and 0.21 ± 0.28 mg bird−1 hr−1 from the layer barn. Carbon dioxide emission factors from the broiler barns with mud and cement floors were 9327 ± 3508 and 25526 ± 6904 mg bird−1 hr−1 respectively, and 8942 ± 36756 mg bird−1 hr−1 from the layer barn. When scaled per livestock unit (LU), where 1 LU is 500 kg bird weight, CH4 emissions were 0.16 ± 0.17 and 0.06 ± 0.03 g LU−1 hr−1 from the broiler barns, and 0.19 ± 0.14 g LU−1 hr−1 from the layer barn. Nitrous oxide emissions were 2.16 ± 1.69 and 0.28 ± 0.17 g LU−1 hr−1 from the broiler barns, and 0.05 ± 0.07 g LU−1 hr−1 from the layer barn. Broilers reared in management systems with wood shavings on mud floor had relatively high CH4 and N2O emissions compared to broilers on wood shavings and cement floor, with the contrary observed for CO2. The emissions N2O were significantly higher from broiler barns compared to layer barns. Emissions were higher in the mornings compared to later periods of the day. Given the observed results, GHG emission mitigation strategies need to be customised for each building design and management system.

The current state of CO2 flux chamber studies in the Arctic tundra

The Arctic tundra plays an important role in the carbon cycle as it stores 50% of global soil organic carbon reservoirs. The processes (fluxes) regulating these stocks are predicted to change due to direct and indirect effects of climate change. Understanding the current and future carbon balance calls for a summary of the level of knowledge regarding chamber-derived carbon dioxide (CO2) flux studies. Here, we describe progress from recently (2000–2016) published studies of growing-season CO2 flux chamber measurements, namely GPP (gross primary production), ER (ecosystem respiration), and NEE (net ecosystem exchange), in the tundra region. We review the study areas and designs along with the explanatory environmental drivers used. Most of the studies were conducted in Alaska and Fennoscandia, and we stress the need for measuring fluxes in other tundra regions, particularly in more extreme climatic, productivity, and soil conditions. Soil respiration and other greenhouse gas measurements were seldom included in the studies. Although most of the environmental drivers of CO2 fluxes have been relatively well investigated (such as the effect of vegetation type and soil microclimate on fluxes), soil nutrients, other greenhouse gases and disturbance regimes require more research as they might define the future carbon balance. Particular attention should be paid to the effects of shrubification, geomorphology, and other disturbance effects such as fire events, and disease and herbivore outbreaks. An improved conceptual framework and understanding of underlying processes of biosphere–atmosphere CO2 exchange will provide more information on carbon cycling in the tundra.

Shifts from methyl chloride sink to source functions within a coastal salt marsh in eastern China: an examination of the effects of biomass burning prohibition policies.

Our previous study found that a salt marsh in eastern China can act as a large CH3Cl sink. One striking finding of this previous study was a strong relationship between high-ambient CH3Cl concentrations and fluxes during the growing season. Moreover, the high-ambient CH3Cl concentration was likely to be related to local biomass burning. However, implementation of biomass burning prohibition policies has effectively reduced biomass burning. Therefore, we predicted that the prohibition of biomass burning would alter CH3Cl concentration and flux within the eastern Chinese coastal salt marsh. In this study, we used static flux chambers to measure CH3Cl fluxes in the early (July of 2004 and January of 2005) and middle-late stages (August and December of 2013) of biomass burning prohibition of along a creek and vegetation transects of the salt marsh. After implementation of the biomass burning prohibition, the concentration and flux of CH3Cl directly related to biomass burning changed remarkably. During the middle-late stage of prohibition, the initial CH3Cl concentration was significantly reduced compared to during the early stage of prohibition. Reductions in atmospheric CH3Cl concentration were especially apparent during the growing season, when biomass burning was prohibited and atmospheric CH3Cl concentration dropped to levels nearly as low as the Northern Hemisphere background concentration. Atmospheric CH3Cl concentration significantly varied throughout the salt marsh, with the highest concentrations appearing over the inland areas and mudflat and lower values occurring over the middle locations. This spatial distribution of CH3Cl may have been directly related to the existence and distribution of potential CH3Cl sources, such as coastal seawater, terrestrial biomass burning, and senescent and decaying aboveground biomass. These changes in initial CH3Cl concentration caused by the biomass burning prohibition may eventually lead to shift in the salt marsh from the tendency to act as a CH3Cl sink to the tendency to act as a CH3Cl source. When the initial atmospheric CH3Cl concentration was high, the vegetation stands acted as CH3Cl sinks. Conversely, they became CH3Cl sources. Therefore, we conclude that the biomass burning prohibition altered the ecosystem-atmosphere exchange of CH3Cl within the studied eastern Chinese coastal salt marsh.

Emissions of organic compounds from produced water ponds I: Characteristics and speciation

We measured fluxes of methane, a suite of non-methane hydrocarbons (C2–C11), light alcohols, and carbon dioxide from oil and gas produced water storage and disposal ponds in Utah (Uinta Basin) and Wyoming (Upper Green River Basin) United States during 2013–2016. In this paper, we discuss the characteristics of produced water composition and air-water fluxes, with a focus on flux chamber measurements. In companion papers, we will (1) report on inverse modeling methods used to estimate emissions from produced water ponds, including comparisons with flux chamber measurements, and (2) discuss the development of mass transfer coefficients to estimate emissions and place emissions from produced water ponds in the context of all regional oil and gas-related emissions.Alcohols (made up mostly of methanol) were the most abundant organic compound group in produced water (91% of total volatile organic concentration, with upper and lower 95% confidence levels of 89 and 93%) but accounted for only 34% (28 to 41%) of total organic compound fluxes from produced water ponds. Non-methane hydrocarbons, which are much less water-soluble than methanol and less abundant in produced water, accounted for the majority of emitted organics. C6–C9 alkanes and aromatics dominated hydrocarbon fluxes, perhaps because lighter hydrocarbons had already volatilized from produced water prior to its arrival in storage or disposal ponds, while heavier hydrocarbons are less water soluble and less volatile. Fluxes of formaldehyde and other carbonyls were low (1% (1 to 2%) of total organic compound flux). The speciation and magnitude of fluxes varied strongly across the facilities measured and with the amount of time water had been exposed to the atmosphere. The presence or absence of ice also impacted fluxes.

Using dynamic flux chambers to estimate the natural attenuation rates in the subsurface at petroleum contaminated sites

In this work, we introduce a screening method for the evaluation of the natural attenuation rates in the subsurface at sites contaminated by petroleum hydrocarbons. The method is based on the combination of the data obtained from standard source characterization with dynamic flux chambers measurements. The natural attenuation rates are calculated as difference between the flux of contaminants estimated with a non-reactive diffusive model starting from the concentrations of the contaminants detected in the source (soil and/or groundwater) and the effective emission rate of the contaminants measured using dynamic flux chambers installed at ground level. The reliability of this approach was tested in a contaminated site characterized by the presence of BTEX in soil and groundwater. Namely, the BTEX emission rates from the subsurface were measured in 4 seasonal campaigns using dynamic flux chambers installed in 14 sampling points. The comparison of measured fluxes with those predicted using a non-reactive diffusive model, starting from the source concentrations, showed that, in line with other recent studies, the modelling approach can overestimate the expected outdoor concentration of petroleum hydrocarbons even up to 4 orders of magnitude. On the other hand, by coupling the measured data with the fluxes estimated with the diffusive non-reactive model, it was possible to perform a mass balance to evaluate the natural attenuation loss rates of petroleum hydrocarbons during the migration from the source to ground level. Based on this comparison, the estimated BTEX loss rates in the test site were up to almost 0.5kg/year/m2. These rates are in line with the values reported in the recent literature for natural source zone depletion. In short, the method presented in this work can represent an easy-to-use and cost-effective option that can provide a further line of evidence of natural attenuation rates expected at contaminated sites.

Comparing chemistry and bioactivity of burned vs. decomposed plant litter: different pathways but same result?

Litter burning and biological decomposition are oxidative processes co-occurring in many terrestrial ecosystems, producing organic matter with different chemical properties and differently affecting plant growth and soil microbial activity. We tested the chemical convergence hypothesis, i.e., materials with different initial chemistry converge toward a common profile, with similar biological effects, as the oxidative process advances, for burning and decomposition. We compared the molecular composition, assessed by 13 C NMR, of seven plant litter types either fresh, decomposed for 30, 90, 180d in a microcosms incubation experiment, or heated at 100°C, 200°C, 300°C, 400°C, 500°C for 30 minutes. We used litter water extracts (5% dry weight) as treatments in bioassays on plant (Lepidium sativum) and fungal (Aspergillus niger) growth, and a washed quartz sand amended with litter (0.5% dw) to assess heterotrophic respiration by flux chamber (i.e., [μg of CO2 released]·[g added litter]-1 ·d-1 ). We observed different molecular variations for materials either burning (i.e., a sharp increase of aromatic C and a decrease of other fractions above 200°C) or decomposing (i.e., early increase of alkyl, methoxyl, and N-alkyl C and decrease of O-alkyl and di-O-alkyl C fractions). Soil respiration and fungal growth decreased with litter age and heating severity, down to 20% relative to fresh litter. Plants were inhibited on fresh litter (on average 13% of the control), but recovered on aged (180d) and heated (30min at 500°C) materials, up to 126% and 63% of the control, respectively. Correlation between the intensity of 13 C NMR signals in litter spectra and bioassay results showed that O-alkyl, methoxyl, and aromatic C fractions are crucial to understand organic matter effects, with plant response negatively affected by labile C but positively associated to lignification and pyrogenic C. The pattern of association of soil respiration and fungal growth to these C fractions was essentially opposite to that observed for plant root growth. Our findings suggest a functional convergence of decomposed and burned organic substrates, emerging from the balance between the bioavailability of labile C sources and the presence of recalcitrant and pyrogenic compounds, oppositely affecting different trophic levels.

Methane emissions from a landfill in north-east India: Performance of various landfill gas emission models.

Rapid urbanization and economic growth has led to significant increase in municipal solid waste generation in India during the last few decades and its management has become a major issue because of poor waste management practices. Solid waste generated is deposited into open dumping sites with hardly any segregation and processing. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the major greenhouse gases that are released from the landfill sites due to the biodegradation of organic matter. In this present study, CH4 and CO2 emissions from a landfill in north-east India are estimated using a flux chamber during September, 2015 to August, 2016. The average emission rates of CH4 and CO2 are 68 and 92mg/min/m2, respectively. The emissions are highest in the summer whilst being lowest in winter. The diurnal variation of emissions indicated that the emissions follow a trend similar to temperature in all the seasons. Correlation coefficients of CH4 and temperature in summer, monsoon and winter are 0.99, 0.87 and 0.97, respectively. The measured CH4 in this study is in the range of other studies around the world. Modified Triangular Method (MTM), IPCC model and the USEPA Landfill gas emissions model (LandGEM) were used to predict the CH4 emissions during the study year. The consequent simulation results indicate that the MTM, LandGEM-Clean Air Act, LandGEM-Inventory and IPCC models predict 1.9, 3.3, 1.6 and 1.4 times of the measured CH4 emission flux in this study. Assuming that this higher prediction of CH4 levels observed in this study holds well for other landfills in this region, a new CH4 emission inventory (Units: Tonnes/year), with a resolution of 0.10×0.10 has been developed. This study stresses the importance of biodegradable composition of waste and meteorology, and also points out the drawbacks of the widely used landfill emission models.

The denitrification paradox: The role of O2 in sediment N2O production

We designed a novel laboratory sediment flux chamber in which we maintained the headspace O2 partial pressure at preselected values, allowing us to experimentally regulate “in-situ” O2 to evaluate its role in net N2O production by an intertidal estuarine sediment (Tyne, UK). In short-term (30 h) incubations with 10 L of overlying estuarine water (∼3 cm depth) and headspace O2 regulation (headspace: sediment/water ratio ∼9:1), net N2O production was highest at 1.2% O2 (sub-oxic; 32.3 nmol N2O m−2 d−1), an order of magnitude higher than at either 0.0% (anoxic; 2.5 N2O nmol m−2 d−1) or 20.85% (ambient; 2.3 nmol N2O m−2 d−1) O2. In a longer-term sealed incubation (∼490 h) without O2 control, time-dependent behaviour of N2O in the tank headspace was highly non-linear with time, showing distinct phases: (i) an initial period of no or little change in O2 or N2O up to ∼ 100 h; (ii) a quasi-linear, inverse correlation between O2 and N2O to ∼360 h, in which O2 declined to ∼2.1% and N2O rose to ∼7800 natm; (iii) over the following 50 h a slower O2 decline, to ∼1.1%, and a more rapid N2O increase, to ∼12000 natm; (iv) over the next 24 h a slowed O2 decline towards undetectable levels and a sharp fall in N2O to ∼4600 natm; (iv) a continued N2O decrease at zero O2, to ∼3000 natm by ∼ 490 h. These results show clearly that rapid N2O consumption (∼115 nmol m−2 d−1), presumably via heterotrophic denitrification (HD), occurs under fully anoxic conditions and therefore that N2O production, which was optimal for sub-oxic O2, results from other nitrogen transformation processes. In experiments in which we amended sediment overlying water to either 1 mM NH4+ or 1 mM NO3−, N2O production rates were 2–134 nmol N2O m−2 d−1 (NH4+ addition) and 0.4–2.2 nmol N2O m−2 d−1 (NO3− addition). We conclude that processes involving NH4+ oxidation (nitrifier nitrification; nitrifier denitrification; nitrification-coupled denitrification) are principally responsible for N2O production in Tyne sediments. Highest N2O production occurred under sub-oxic headspace (∼1.2 O2%) incubations. Anoxic sediments where HD was isolated acted as periodic N2O sinks or relatively small sources of N2O. Our experimental approach thus gives valuable insight into the O2 effect on N2O fluxes from intertidal sediments.

Standing Dead Trees are a Conduit for the Atmospheric Flux of CH4 and CO2 from Wetlands

In vegetated wetland ecosystems, plants can be a dominant pathway in the atmospheric flux of methane, a potent greenhouse gas. Although the roles of herbaceous vegetation and live woody vegetation in this flux have been established, the role of dead woody vegetation is not yet known. In a restored wetland of North Carolina’s coastal plain, static flux chambers were deployed at two heights on standing dead trees to determine if these structures acted as a conduit for methane emissions. Methane fluxes to the atmosphere were measured in five of the chambers, with a mean flux of 0.4 ± 0.1 mg m−2 h−1. Methane consumption was also measured in three of the chambers, with a mean flux of −0.6 ± 0.3 mg m−2 h−1. Standing dead trees were also a source of the flux of CO2 (114.6 ± 23.8 mg m−2 h−1) to the atmosphere. Results confirm that standing dead trees represent a conduit for the atmospheric flux of carbon gases from wetlands. However, several questions remain regarding the ultimate source of these carbon gases, the controls on the magnitude and direction of this flux, the mechanisms that induce this flux, and the importance of this pathway relative to other sources at the landscape level.

Comparative study of elemental mercury flux measurement techniques over a Fennoscandian boreal peatland

Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon® dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0–34 cm) was identified by measuring total mercury in eight peat cores (57 ± 8 ng g−1, average ± SE), vascular plant coverage (32–52%), water table level (4.5–14.1 cm) and dissolved gaseous elemental mercury concentrations (28–51 pg L−1) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, α = 0.05). Even though the correlation between the Teflon® DFC and Aero-DFC was significant (r = 0.76, p < 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m−2 h−1) and REA (2 ng m−2 h−1) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers (<0.2 m2) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity.

Autonomous mobile platform for monitoring air emissions from industrial and municipal wastewater ponds

ABSTRACTSignificant amounts of volatile organic compounds and greenhouse gases are generated from wastewater lagoons and tailings ponds in Alberta, Canada. Accurate measurements of these air pollutants and greenhouse gases are needed to support management and regulatory decisions. A mobile platform was developed to measure air emissions from tailings pond in the oil sands region of Alberta. The mobile platform was tested in 2015 in a municipal wastewater treatment lagoon. With a flux chamber and a CO2/CH4 sensor on board, the mobile platform was able to measure CO2 and CH4 emissions over two days at two different locations in the pond. Flux emission rates of CO2 and CH4 that were measured over the study period suggest the presence of aerobic and anaerobic zones in the wastewater treatment lagoon. The study demonstrated the capabilities of the mobile platform in measuring fugitive air emissions and identified the potential for the applications in air and water quality monitoring programs.Implications: The Mobile Platform demonstrated in this study has the ability to measure greenhouse gas (GHG) emissions from fugitive sources such as municipal wastewater lagoons. This technology can be used to measure emission fluxes from tailings ponds with better detection of spatial and temporal variations of fugitive emissions. Additional air and water sampling equipment could be added to the mobile platform for a broad range of air and water quality studies in the oil sands region of Alberta.