Gas Flux Measurements Research Articles

Rh-Chamber: A Novel Chamber Design for Gas Sampling in the Coastal Sediment and Water Surface

This research aims to develop and test Rh-Chamber, an innovative gas sampling tool designed for coastal environments. The coastal environment is a dynamic ecosystem that plays an important role in the global biogeochemical cycle, especially in the production and release of greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Until now, existing gas sampling methods have limitations, especially in maintaining representative field conditions and capturing temporal dynamics of gas release. The Rh-Chamber comes as a highly flexible solution, allowing sampling both on coastal sediments and on the water surface. The design consists of a gas incubator, a float and a ballast, which allows the appliance to function optimally in various current and sediment conditions. Gas sampling is done manually using syiringe, with varying time intervals. The results show that Rh-Chamber provides better accuracy in measuring gas flux in coastal ecosystems than conventional methods. These innovations also have the potential to be used in climate change research, especially to evaluate the contribution of coastal ecosystems to greenhouse gas emissions. Although there are some limitations, such as the need for additional manpower in its operation in deeper waters, the Rh-Chamber makes a significant contribution to coastal environmental research.

Groundwater level effects on greenhouse gas emissions from undisturbed peat cores

Peat soils store a large part of the global soil carbon stock, which can potentially be lost when they are drained and taken into cultivation, resulting in CO2 emission and land subsidence. Groundwater level (GWL) management has been proposed to mitigate peat oxidation, but may lead to increased emissions of nitrous oxide (N2O) and methane (CH4).The aim of this experiment was to study trade-offs between greenhouse gas emissions from peat soils as a function of GWL. We incubated 1 m deep, 24 cm diameter undisturbed bare soil cores, after removal of the grass layer, from three contrasting Dutch grassland peat sites for 370 days at 16 °C. The cores were subjected to drying-wetting cycles, with the GWL varying between near the soil surface to 160 cm below the surface. We measured gas fluxes of CO2, N2O and CH4 from the soil surface, extracted pore water for DOC and mineral nitrogen analysis, and measured soil hydraulic and shrinkage characteristics.Emissions of CO2 increased after lowering the GWL, but showed different GWL-response curves during rewetting of the soil. On average, highest CO2 emissions of 1.5 g C·m−2 day−1 were found at a GWL of 80 cm below the surface. However, the 0 cm GWL was the only treatment with significantly lower CO2 emissions than other GWLs. Cumulative CO2 emissions differed significantly between sampling sites. Emissions of N2O showed a different response, peaking at GWL heights above −20 cm, particularly after a recent GWL rise. Though not significantly different, the highest N2O emissions were measured at the 0 cm GWL treatment. We confirmed this pattern for N2O in un-replicated soil cores with grass sward, although emission values were lower in these cores due to the root uptake of mineral nitrogen. CH4 emissions or −uptake remained low under any GWL. We conclude that raising the GWL is a successful strategy to reduce CO2 emissions from peat oxidation. However, raising the GWL close to the soil surface could lead to N2O emissions that negate any gains in terms of global warming potential. Our results suggest that raising the GWL in peat grasslands to −20 cm creates such a risk. A constant GWL at the surface (0 cm) would be preferential for mitigating both CO2 and N2O emissions, although such conditions don’t allow for agricultural grass production (mowing or grazing).

A high‐frequency greenhouse gas flux analysis tool: Insights from automated non‐steady‐state transparent soil chambers

AbstractNon‐steady‐state chambers are widely employed for quantifying soil emissions of CO2, CH4, and N2O. Automated non‐steady‐state (a‐NSS) soil chambers, when coupled with online gas analysers, offer the ability to capture high‐frequency measurements of greenhouse gas (GHG) fluxes. While these sampling systems provide valuable insights into GHG emissions, they present post‐measurement challenges, including the management of extensive datasets, intricate flux calculations, and considerations for temporal upscaling. In this study, a computationally efficient algorithm was developed to compute instantaneous fluxes and estimate diel flux patterns using continuous, high‐resolution data obtained from an a‐NSS sampling system. Applied to a 38‐day dataset, the algorithm captured concurrent field measurements of CO2, CH4, and N2O fluxes. The automated sampling system enables the acquisition of high‐frequency data, allowing the detection of episodic gas flux events. By using shape‐constrained additive models, a median percentage deviation (bias) of −1.031 and −4.340% was achieved for CO2 and N2O fluxes, respectively. Simpson's rule allowed for efficient upscale from instantaneous to diel flux values. As a result, the proposed algorithm can rapidly and simultaneously calculate CO2, CH4, and N2O fluxes, providing both instantaneous and diel values directly from raw, high‐temporal‐resolution data. These advancements significantly contribute to the field of GHG flux measurement, enhancing both the efficiency and accuracy of calculations for a‐NSS soil chambers and deepening our understanding of GHG emissions and their temporal dynamics.

Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer.

Measuring greenhouse gas (GHG) fluxes and pools in ecosystems are becoming increasingly common in ecological studies due to their relevance to climate change. With it, the need for analytical platforms adaptable to measuring different pools and fluxes within research groups also grows. This study aims to develop a procedure to use portable optical spectroscopy-based gas analyzers, originally designed and marketed for gas flux measurements, to measure GHG concentrations in aqueous samples. The protocol involves the traditional headspace equilibration technique followed by the injection of a headspace gas subsample into a chamber connected through a closed loop to the inlet and outlet ports of the gas analyzer. The chamber is fabricated from a generic mason jar and simple laboratory supplies, and it is an ideal solution for samples that may require pre-injection dilution. Methane concentrations measured with the chamber are tightly correlated (r2 > 0.98) with concentrations determined separately through gas chromatography-flame ionization detection (GC-FID) on subsamples from the same vials. The procedure is particularly relevant for field studies in remote areas where chromatography equipment and supplies are not readily available, offering a practical, cheaper, and more efficient solution for measuring methane and other dissolved greenhouse gas concentrations in aquatic systems.

Quantifying the carbon sequestration potential of different soil management practices aimed at increasing organic content in soil and reducing the usage of chemical inputs

<p>The global imperative to address climate change and promote sustainable agriculture has underscored the critical role of soil management practices in enhancing carbon sequestration and reducing greenhouse gas emissions. This research focuses on quantifying the carbon sequestration potential of diverse soil management techniques aimed at increasing organic content in soil while minimizing the use of chemical inputs. It integrates a multidisciplinary approach, conducting field experiments across diverse agroecological regions with different soil types and cropping systems. Key practices under investigation include cover cropping, crop rotations, conservation tillage, compost application, organic amendments, integrated pest management (IPM), and precision agriculture. The study assesses their impact on soil organic carbon levels, greenhouse gas emissions, soil health indicators, and crop productivity through comprehensive data collection and analysis techniques. Statistical analyses and modeling are employed to quantify carbon sequestration rates, evaluate treatment effects, and assess environmental and agronomic benefits. These practices are implemented in controlled trials to assess their impact on soil organic carbon (SOC) levels, greenhouse gas emissions (CO2, CH4, N2O), soil health indicators (microbial biomass, nutrient cycling, soil structure), and crop productivity. Data collection and analysis techniques involve comprehensive soil sampling, greenhouse gas flux measurements, soil health assessments, and crop yield monitoring over multiple growing seasons. Statistical analyses and modeling approaches are employed to quantify the carbon sequestration rates, assess treatment effects on soil health and greenhouse gas emissions, and evaluate the overall environmental and agronomic benefits of the soil management practices. The study aims to contribute valuable insights into evidence-based strategies for promoting sustainable soil management practices that enhance carbon sequestration while maintaining or improving agricultural productivity. The findings will have implications for informing agricultural policies, guiding farm management decisions, and advancing research on climate-smart agriculture. By quantifying the carbon sequestration potential of different soil management practices, this research contributes to the broader goal of achieving climate resilience, environmental sustainability, and food security in agricultural systems.</p>

Mix-method toolbox for monitoring greenhouse gas production and microbiome responses to soil amendments

In this study, we adopt an interdisciplinary approach, integrating agronomic field experiments with soil chemistry, molecular biology techniques, and statistics to investigate the impact of organic residue amendments, such as vinasse (a by-product of sugarcane ethanol production), on soil microbiome and greenhouse gas (GHG) production. The research investigates the effects of distinct disturbances, including organic residue application alone or combined with inorganic N fertilizer on the environment. The methods assess soil microbiome dynamics (composition and function), GHG emissions, and plant productivity. Detailed steps for field experimental setup, soil sampling, soil chemical analyses, determination of bacterial and fungal community diversity, quantification of genes related to nitrification and denitrification pathways, measurement and analysis of gas fluxes (N2O, CH4, and CO2), and determination of plant productivity are provided. The outcomes of the methods are detailed in our publications (Lourenço et al., 2018a; Lourenço et al., 2018b; Lourenço et al., 2019; Lourenço et al., 2020). Additionally, the statistical methods and scripts used for analyzing large datasets are outlined. The aim is to assist researchers by addressing common challenges in large-scale field experiments, offering practical recommendations to avoid common pitfalls, and proposing potential analyses, thereby encouraging collaboration among diverse research groups.•Interdisciplinary methods and scientific questions allow for exploring broader interconnected environmental problems.•The proposed method can serve as a model and protocol for evaluating the impact of soil amendments on soil microbiome, GHG emissions, and plant productivity, promoting more sustainable management practices.•Time-series data can offer detailed insights into specific ecosystems, particularly concerning soil microbiota (taxonomy and functions).

Assessment of smoke plume height products derived from multisource satellite observations using lidar-derived height metrics for wildfires in the western US

Abstract. As wildfires intensify and fire seasons lengthen across the western US, the development of models that can predict smoke plume concentrations and track wildfire-induced air pollution exposures has become critical. Wildfire smoke plume height is a key indicator of the vertical placement of plume mass emitted from wildfire-related aerosol sources in climate and air quality models. With advancements in Earth observation (EO) satellites, spaceborne products for aerosol layer height or plume injection height have recently emerged with increased global-scale spatiotemporal resolution. However, to evaluate column radiative effects and refine satellite algorithms, vertical profiles of regionally representative aerosol properties from wildfires need to be measured directly. In this study, we conducted the first comprehensive evaluation of four passive satellite remote-sensing techniques specifically designed for retrieving plume height. We compared these satellite products with the airborne Wyoming Cloud Lidar (WCL) measurements during the 2018 Biomass Burning Flux Measurements of Trace Gases and Aerosols (BB-FLUX) field campaign in the western US. Two definitions, namely, “plume top” and “extinction-weighted mean plume height”, were used to derive the representative heights of wildfire smoke plumes, based on the WCL-derived vertical aerosol extinction coefficient profiles. Using these two definitions, we performed a comparative analysis of multisource satellite-derived plume height products for wildfire smoke. We provide a discussion related to which satellite product is most appropriate for determining plume height characteristics near a fire event or estimating downwind plume rise equivalent height, under multiple aerosol loadings. Our findings highlight the importance of understanding the sensitivity of different passive remote-sensing techniques on space-based wildfire smoke plume height observations, in order to resolve ambiguity surrounding the concept of “effective smoke plume height”. As additional aerosol-observing satellites are planned in the coming years, our results will inform future remote-sensing missions and EO satellite algorithm development. This bridges the gap between satellite observations and plume rise modeling to further investigate the vertical distribution of wildfire smoke aerosols.

Recommendations on visit duration and sample number requirements for an automated head chamber system.

Automated head chamber systems (AHCS; GreenFeed, C-Lock Inc., Rapid City, SD) increasingly are being used for measuring the gas flux of unrestrained cattle. There are a wide range of recommendations for what constitutes a "good" visit (i.e., duration) to an AHCS and how many visits are required for the AHCS to quantify gas fluxes accurately and precisely. Accordingly, the purpose of this experiment was to investigate the effects of visit duration thresholds and the subsequent effects of these thresholds on the number of visits needed to provide adequate estimates of carbon dioxide (CO2) and methane (CH4) emissions, and oxygen (O2) consumption by beef cattle. This analysis utilized data from three previously published experiments with grazing beef steers and one experiment with finishing beef steers, with 103 steers total. When comparing all available visits, there was excellent agreement [Lin's concordance correlation coefficient (CCC) ≥ 0.96] between visits ≥ 3min in duration and those ≥ 2min for the three gases in all four experiments. When data from all four experiments were pooled, there was excellent agreement between visits ≥ 3min and those ≥ 2min and ≥ 1min for all gases (CCC ≥ 0.96). These results suggest that estimates from visits ≥ 2min are like those from visits ≥ 3min. Next, we investigated if including visits ≥ 2min or ≥ 1min would increase the minimal number of visits required to provide excellent agreement with the "gold-standard" (mean of all visits ≥ 3min). For this, we used only one of the experiments and randomly selected visits per animal ranging from n = 5 to 60, in increments of 5. The sole experiment was used because all animals had more than 60 visits. We then assessed the agreement between the "gold-standard" (mean of all visits ≥ 3min [144 ± 55.01 visits per steer]) estimates of CO2, O2, and CH4. The minimum number of visits required to achieve excellent agreement (CCC ≥ 0.90) to the "gold-standard" estimate for all gases was 30 visits ≥ 3min in duration, or 40 visits ≥ 2min in duration. Visits ≥ 1min in duration did not achieve excellent agreement, even when 60 were used. Based on these results, we recommend excluding visits < 3min in duration with 30 minimum visit records per animal. However, if researchers choose to implement a 2-min visit duration threshold then 40 visit records are needed per animal.

Identifying landscape hot and cold spots of soil greenhouse gas fluxes by combining field measurements and remote sensing data

Abstract. Upscaling chamber measurements of soil greenhouse gas (GHG) fluxes from point scale to landscape scale remain challenging due to the high variability in the fluxes in space and time. This study measured GHG fluxes and soil parameters at selected point locations (n=268), thereby implementing a stratified sampling approach on a mixed-land-use landscape (∼5.8 km2). Based on these field-based measurements and remotely sensed data on landscape and vegetation properties, we used random forest (RF) models to predict GHG fluxes at a landscape scale (1 m resolution) in summer and autumn. The RF models, combining field-measured soil parameters and remotely sensed data, outperformed those with field-measured predictors or remotely sensed data alone. Available satellite data products from Sentinel-2 on vegetation cover and water content played a more significant role than those attributes derived from a digital elevation model, possibly due to their ability to capture both spatial and seasonal changes in the ecosystem parameters within the landscape. Similar seasonal patterns of higher soil/ecosystem respiration (SR/ER–CO2) and nitrous oxide (N2O) fluxes in summer and higher methane (CH4) uptake in autumn were observed in both the measured and predicted landscape fluxes. Based on the upscaled fluxes, we also assessed the contribution of hot spots to the total landscape fluxes. The identified emission hot spots occupied a small landscape area (7 % to 16 %) but accounted for up to 42 % of the landscape GHG fluxes. Our study showed that combining remotely sensed data with chamber measurements and soil properties is a promising approach for identifying spatial patterns and hot spots of GHG fluxes across heterogeneous landscapes. Such information may be used to inform targeted mitigation strategies at the landscape scale.

Testing external photoevaporation in the σ-Orionis cluster with spectroscopy and disk mass measurements (Corrigendum)

{The evolution of protoplanetary disks is regulated by an interplay of several processes, either internal to the system or related to the environment. As most of the stars and planets, including our own Solar System, have formed in massive stellar clusters that contain OB-type stars, studying the effects of UV radiation on disk evolution is of paramount importance.} % aims heading (mandatory) {Here we test the impact of external photoevaporation on the evolution of disks in the mid-age ($sim$3--5 Myr) $sigma$-Orionis cluster by conducting the first combined large-scale UV to IR spectroscopic and mm-continuum survey of this region.} % methods heading (mandatory) {We study a sample of 50 targets located at increasing distances from the central, massive OB system $sigma$-Ori. We combine new spectra obtained with VLT/X-Shooter, used to measure mass accretion rates and stellar masses, with new and previously published ALMA measurements of disk dust and gas fluxes and masses.} % results heading (mandatory) {We confirm the previously found decrease of $M_{rm dust}$ in the inner $sim$0.5 pc of the cluster, and discover an additional dependence with the stellar host mass. The disks around the more massive stars ($ge$ 0.4msun) and located in the inner part ($&lt;$ 0.5 pc) of the cluster have $M_{rm dust}$ about an order of magnitude lower than the more distant ones, in contrast to the rather flat $M_{rm dust}$ distribution as a function of the projected separation from $sigma$-Ori, for the disks around the lowest-mass stars in the sample. About half of the sample is located in the region of the $dot{M}_{rm acc}$ vs $M_{rm disk}$ expected by models of external photoevaporation, i.e. showing shorter disk lifetimes than expected for their ages. The shorter disk lifetimes is observed for all targets with projected separation from $sigma$-Ori $&lt;$ 0.5 pc, proving that the presence of a massive stellar system affects disk evolution. } % conclusions heading (optional), leave it empty if necessary {External photoevaporation is a viable mechanism to explain the observed shorter disk lifetimes and lower $M_{rm dust}$ in the inner $sim$0.5 pc of the $sigma$-Orionis cluster, where the effects of this process are more pronounced. Follow-up observations of the low stellar mass targets are crucial to constrain disk dispersion time scales in the cluster and to confirm the dependence of the external photoevaporation process with stellar host mass. This work confirms that the effects of external photoevaporation are significant down to at least impinging radiation as low as $sim 10^{4}$ G$_0$. }

Numerical modelling of the volcanic plume dispersion from the hydrothermal system of La Soufrière de Guadeloupe

Passive volcanic degassing results in the emission of toxic gases such as H2S at quasi-steady rates over long periods of time that pose a significant hazard to human health even in low gas concentrations. Currently, La Soufrière de Guadeloupe has one of the highest gas emission rates in the Lesser Antilles arc, with gas emitted mainly from low-temperature fumaroles. In this study, gas dispersion from the volcano between 2016–2021 was modelled using a numerical code that takes into account wind and atmospheric data, topography and gas flux measurements. We ran c.100 individual simulations of the most frequently observed wind and gas flux conditions using a Monte-Carlo scheme. Our results, validated using air-quality measurements and citizen-science surveys, show that the most exposed zones are the hamlet of Matouba and the upper St. Claude. These areas have 20% and 5% probability, respectively, of exceeding H2S guidelines for long-term gas exposure (70 ppb).

Direct measurements of gas flux at seep sites using a broadband split-beam echosounder

Measurement of methane gas flux from oceanic seep sites is challenging, given the ephemeral nature and the heterogeneous spatial distribution of seeps. Acoustic systems offer a solution, as they make synoptic measurements of the water column, and the gas bubbles are strong acoustic scatterers. Here, we present a method to directly estimate gas flux using a calibrated broadband split-beam echosounder. The vertical range resolution of the broadband system facilitates discrimination of individual bubbles in the acoustic record. By comparing measurements of bubble target strength to an analytical scattering model, bubble radii can be directly measured from the acoustic data. Concurrently, split-aperture processing allows for the precise tracking of bubbles as they rise from the seafloor for measurement of bubble rise velocity. Together, the observations of bubble radius and rise velocity offer a measure of gas flux, requiring nothing more than a vessel transiting over a seep site. Application of this method to seep data collected on the East Siberian Arctic Shelf shows good agreement between resulting measurements of bubble radii (0.68–8.40 mm) with those made using optical sensors, and bubble rise velocities (4–36 cm/s) are consistent with published measurements and models. Extrapolating from single bubbles measurements, our estimates of regional methane flux (2.9 × 104 kg/year) suggest that carbon emissions in this region may be lower than previously believed.

Vertical information of CO from TROPOMI total column measurements in context of the CAMS-IFS data assimilation scheme

Abstract. Since 2017 the Tropospheric Monitoring Instrument (TROPOMI) on board ESA's Copernicus Sentinel-5 satellite (S5-P) has provided the operational carbon monoxide (CO) data product with daily global coverage on a spatial resolution of 5.5×7 km2. The European Centre for Medium-Range Weather Forecasts (ECMWF) plans to assimilate the retrieved total columns and the corresponding vertical sensitivities in the Copernicus Atmosphere Monitoring Service Integrated Forecasting System (CAMS-IFS) to improve forecasts of the atmospheric chemical composition. The TROPOMI data will primarily constrain the vertical integrated CO field of CAMS-IFS but to a lesser extent also its vertical CO distribution. For clear-sky conditions, the vertical sensitivity of the TROPOMI CO data product is useful throughout the atmosphere, but for cloudy scenes it varies due to cloud shielding and light scattering. To assess the profile information, we deploy an a posteriori profile retrieval that combines an ensemble of TROPOMI CO column retrievals with different vertical sensitivities to obtain a vertical CO profile that is then a representative average for the chosen spatial and temporal domain. We demonstrate the approach on three CO pollution cases. For the so-called “Rabbit Foot Fire” in Idaho on 12 August 2018, we estimate a CO profile showing the pollution at an altitude of about 5 km in good agreement with airborne in situ measurements of the Biomass Burning Flux Measurements of Trace Gases and Aerosol (BB-FLUX) field campaign. The distinct CO enhancement in a plume aloft (length =212 km, width =34 km), decoupled from the ground, is sensed by TROPOMI but is not present in the CAMS-IFS model. For a large-scale event, we analyzed the CO pollution from Siberian wildfires that took place from 14 to 17 August 2018. The TROPOMI data estimate the height of the pollution plume over Canada at 7 km in agreement with CAMS-IFS. However, CAMS-IFS underestimates the enhanced CO vertical column densities sensed by TROPOMI within the plume by more than 100 ppb. Finally, we study the seasonal biomass burning in the Amazon. During the burning season the CO profile retrieved from the TROPOMI measurements (1–15 August 2019) agrees well with the one of CAMS-IFS with a similar vertical shape between ground and 14 km altitude. Hence, our results indicate that assimilating TROPOMI CO retrieval with different vertical sensitivities (e.g., under clear-sky and cloudy conditions) provides information about the vertical distribution of CO.

A SO2 flux study of the Etna volcano 2020–2021 paroxysmal sequences

The persistent open-vent degassing of Mt. Etna is often punctuated by months-long paroxysmal sequences characterized by episodes of violent Strombolian to lava fountaining activity. Understanding these gas-fueled transitions from quiescence to eruption requires routine measurement of gas fluxes. Here, we report SO2 flux measurements, obtained from a permanent UV camera system, collected over a two-year-long period spanning two paroxysmal sequences of Etna’s New South East Crater (NSEC) in December 2020/April 2021 and May/October 2021. In both cases, SO2 flux increased from ≤ 3250 Mg/day during “ordinary” activity to ≥ 4200 Mg/day. We interpret these distinct SO2 degassing regimes in light of seismic and thermal observations and drawing on numerical simulations of sulfur degassing constrained by parental melt sulfur contents in Etna’s hawaiites. We find that initiation of a paroxysmal sequence results from an approximate doubling of the time-averaged rate of magma supply (and degassing) above the sulfur exsolution level (∼150 MPa pressure), to &amp;gt;4 m3/s. This corroborates recent models that argue for the triggering of paroxysmal sequences by escalating supply of volatile-rich magma to a reservoir ∼3–4 km below the summit region. The non-stationary nature of magma flow and volcanic degassing we identify highlights the need for sustained surveillance to characterize long-term atmospheric budgets of volcanic volatiles.

Eddy correlation measurements to visualize CO2 and water vapor concentrations and fluxes

Eddy correlation measures gas exchange between canopy and the overlying atmosphere by evaluating the correlation between fluctuations in the gas-of-interest’s mixing ratio and the vertical wind velocity and considered the most accurate approach for measuring gas fluxes, mostly carbon dioxide and water vapor under ideal homogeneous conditions. It has been used in micrometeorology for decades to quantify mass and energy transfer between urban, natural and agricultural ecosystems and the atmosphere. We assessed its application under various—homogeneous and non-homogeneous—conditions. Our study indicates that fluxes of CO2 and H2O correlate well with plants activity only when turbulent conditions are present, in open fields. At such conditions, direct measurements of concentration of those gases are not an accurate indicator for plants activity. On the other hand, in closed systems (e.g. greenhouses)- fluxes as measured by an eddy correlation system can't accurately be related to the state of the vegetation, but the fluctuations in the concentrations of CO2 and H2O directly correlate to the actual plants activity. Adapting conditions in greenhouses to limiting factors as temperature, increases CO2 sequestration by plants, and may increase productivity

Assessing the climate change mitigation potential from food waste composting

Food waste is a dominant organic constituent of landfills, and a large global source of greenhouse gases. Composting food waste presents a potential opportunity for emissions reduction, but data on whole pile, commercial-scale emissions and the associated biogeochemical drivers are lacking. We used a non-invasive micrometeorological mass balance approach optimized for three-dimensional commercial-scale windrow compost piles to measure methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions continuously during food waste composting. Greenhouse gas flux measurements were complemented with continuous oxygen (O2) and temperature sensors and intensive sampling for biogeochemical processes. Emission factors (EF) ranged from 6.6 to 8.8 kg CH4–C/Mg wet food waste and were driven primarily by low redox and watering events. Composting resulted in low N2O emissions (0.01 kg N2O–N/Mg wet food waste). The overall EF value (CH4 + N2O) for food waste composting was 926 kgCO2e/Mg of dry food waste. Composting emissions were 38–84% lower than equivalent landfilling fluxes with a potential net minimum savings of 1.4 MMT CO2e for California by year 2025. Our results suggest that food waste composting can help mitigate emissions. Increased turning during the thermophilic phase and less watering overall could potentially further lower emissions.

Relationship between soil CO2 fluxes and soil moisture: Anaerobic sources explain fluxes at high water content

Soil moisture is a known environmental factor influencing carbon dioxide (CO2) emissions and therefore represents an important variable in predictive models. Establishing relationships between soil CO2 emissions and soil moisture has long focused on the role of soil organic carbon mineralization by aerobic respiration. This approach, which generally yields a bell-shaped relationship establishing maximum CO2 production at moderate soil moisture, ignores anaerobic processes as a potential source of CO2. To decouple the effects of soil moisture and O2, we conducted a factorial batch experiment by incubating soil samples at different imposed moisture contents (30%, 45%, 65%, 80%, and 100% water-filled pore space; WFPS) at 25 °C, under both oxic (normal air) and anoxic (N2 atmosphere) headspace conditions. Gas fluxes measured in the oxic incubations show that CO2 fluxes were maximal (31.2 ± 1.8 nmol cm−3 soil hr-1) at moderate moisture content (65% WFPS), as commonly reported. However, contrary to previous models that predict negligible CO2 fluxes under fully saturated conditions due to O2 limitation, substantial fluxes of CO2 (18.1 ± 2.2 nmol cm−3 soil hr-1) were measured at 100% WFPS. In the anoxic treatments, CO2 fluxes rose sharply when the moisture content exceeded 65% WFPS, with values at 100% saturation (21.8 ± 2.2 nmol cm−3 soil hr-1), close to the corresponding fluxes in the oxic incubations. Methane (CH4) fluxes in the anoxic incubations increased over time, ultimately reaching parity with the CO2 fluxes at 100% WFPS. To reproduce the soil moisture dependence of the CO2 fluxes, we propose a kinetic model representing both aerobic and anaerobic CO2 production. Together, the gas flux measurements, porewater geochemistry data, and modeling results indicated that at soil moisture contents approaching saturation (≥90%), anaerobic processes were the major source of CO2 in the oxic incubations. Overall, we conclude that existing models may underrepresent soil CO2 production at high soil moisture by not considering anaerobic reaction pathways releasing CO2.

Variation in methodology obscures clarity of cropland global warming potential estimates.

Global warming potential (GWP) estimates from agroecosystems are valuable for understanding management effects on climate regulation services. However, GWP estimates are complex, including attributes with high spatiotemporal variability. Published GWP estimates from cropland were compiled and methodological attributes known to influence GWP were extracted. Results revealed considerable variation in approaches to estimate GWP. Among carbon balance methods, respiration methods were used most frequently (33%), followed by soil carbon stock change over time (30%). Twenty-six percent of studies did not account for carbon change in GWP estimates. Duration of gas flux measurements ranged from 0.5 to 60 months, with weekly and sub-weekly sampling most common (34% and 33%, respectively). Carbon dioxide equivalent conversion factors generally aligned with Intergovernmental Panel on Climate Change recommendations through 2014 but diverged thereafter. This review suggests the need for increased transparency in how GWP estimates are derived and communicated. Presentation of key metadata alongside GWP estimates is recommended.

Carbon exchange and primary production in a High-Arctic peatland in Svalbard

Moss tundra with a thick peat layer dominated by bryophytes is one of the most important ecosystems in the High Arctic of Svalbard, but little is known about the carbon dynamics of moss tundra. Here, we estimated the net primary production (NPP) and net ecosystem production (NEP) of moss tundra on Brøggerhalvøya (Brøgger Peninsula) of north-western Svalbard (79°N). The net photosynthetic and respiration rates of the two dominant moss species, Calliergon richardsonii and Tomenthypnum nitens, were measured under laboratory conditions. On the basis of the photosynthetic and respiration characteristics and climatic data, we estimated the cumulative NPP of the dominant moss species during the growing season to be 143–207 gC m-2. Net CO2 exchange, which was determined by subtracting the respiration of the brown moss layer from NPP, was similar to that estimated using field gas flux measurements. The field measurements indicated that methane emissions contributed little to carbon flow. The NEP estimated in this study was much larger than the long-term carbon accumulation rate reported in a previous study. These data suggest that a significant amount of fixed carbon was lost from the peat layer or that carbon accumulation has recently increased. The NPP and NEP values of the moss tundra are larger than those reported for other vegetation types in this area, suggesting that moss tundra is an active site with high rates of carbon fixation.

Insights into magma dynamics at Etna (Sicily) from SO2 and HCl fluxes during the 2008–2009 eruption

Abstract Magma convection, where low-viscosity, gas-rich magma ascends, degasses, and crystallizes before sinking down the same conduit in either annular or side-by-side flows, has been proposed for active basaltic volcanoes, where excess gas fluxes relative to erupted lava volume can be observed. Experimental studies show that convection is produced by buoyant ascending gas-rich magma and descending degassed magmas following density difference contrast, while geophysical studies point to the endogenous growth of active volcanoes through magma accumulation in plutons. However, many aspects of the convection process remain unclear, in particular, the depth to which magma ascends before overturning. Models have been proposed where overturn occurs near the surface and also at depths greater than 2 km from the top of the magma-filled conduit. The long-term monitoring of volcanic gas compositions may reveal new insights into the convection process, as each gas has a unique solubility-pressure profile. We report measurements of SO2 and HCl gas fluxes from Etna between October 2007 and May 2011, in which an ~90% collapse in halogen flux was observed together with an effusive eruption. This observation indicates that the halogen fluxes, during quiescent periods on Etna, require both magma supply to the shallowest levels and a period of residence. The lava effusion has the effect of reducing the shallow residence time, drastically reducing the halogen flux. These results provide a new interpretative framework for the degassing process and gas composition monitoring to explain subtle variations in magma supply and residence times in basaltic volcanism.