Gas Flux Measurements Research Articles

Technical note: A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Abstract. Freshwaters emit significant amounts of CO2 on a global scale. However, emissions remain poorly constrained from the diverse range of aquatic systems. The drivers and regulators of CO2 gas flux from standing waters require further investigation to improve knowledge on both global-scale estimates and system-scale carbon balances. Often, lake–atmosphere gas fluxes are estimated from empirical models of gas transfer velocity and air–water concentration gradient. Direct quantification of the gas flux circumvents the uncertainty associated with the use of empirical models from contrasting systems. Existing methods to measure CO2 gas flux are often expensive (e.g. eddy covariance) or require a high workload in order to overcome the limitations of single point measurements using floating chambers. We added a small air pump, a timer and an exterior tube to ventilate the floating chamber headspace and passively regulate excess air pressure. By automating evacuation of the chamber headspace, continuous measurements of lake CO2 gas flux can be obtained with minimal effort. We present the chamber modifications and an example of operation from a small forest lake. The modified floating chamber performed well in the field and enabled continuous measurements of CO2 gas flux with 40 min intervals. Combining the direct measurements of gas flux with measurements of air and waterside CO2 partial pressure also enabled calculation of gas exchange velocity. Building and using the floating chamber is straightforward. However, because an air pump is used to restart measurements by thinning the chamber headspace with atmospheric air, the duration of the air pump pause–pulse cycle is critical and should be adjusted depending on system characteristics. This may result in shorter deployment duration, but this restriction can be circumvented by providing a stronger power source. The simple design makes modifications of the chamber dimensions and technical additions for particular applications and systems easy. This should make this approach to measuring gas flux flexible and appropriate in a wide range of different systems.

Restricting the nonlinearity parameter in soil greenhouse gas flux calculation for more reliable flux estimates.

The static chamber approach is often used for greenhouse gas (GHG) flux measurements, whereby the flux is deduced from the increase of species concentration after closing the chamber. Since this increase changes diffusion gradients between chamber air and soil air, a nonlinear increase is expected. Lateral gas flow and leakages also contribute to non linearity. Several models have been suggested to account for this non linearity, the most recent being the Hutchinson–Mosier regression model (hmr). However, the practical application of these models is challenging because the researcher needs to decide for each flux whether a nonlinear fit is appropriate or exaggerates flux estimates due to measurement artifacts. In the latter case, a flux estimate from the linear model is a more robust solution and introduces less arbitrary uncertainty to the data. We present the new, dynamic and reproducible flux calculation scheme, kappa.max, for an improved trade-off between bias and uncertainty (i.e. accuracy and precision). We develop a tool to simulate, visualise and optimise the flux calculation scheme for any specific static N2O chamber measurement system. The decision procedure and visualisation tools are implemented in a package for the R software. Finally, we demonstrate with this approach the performance of the applied flux calculation scheme for a measured flux dataset to estimate the actual bias and uncertainty. The kappa.max method effectively improved the decision between linear and nonlinear flux estimates reducing the bias at a minimal cost of uncertainty.

Temporal variations and temperature sensitivity of ecosystem respiration in three brackish marsh communities in the Min River Estuary, southeast China

Ecosystem respiration (Reco) is an important pathway for gaseous carbon loss in coastal wetland environments. However, little is known regarding the dynamics of Reco and its temperature sensitivity (Q10) under different tidal stages, and vegetation types. In this study, Reco was measured with dark chambers for nearly 2 years in three different brackish marsh stands dominated by Cyperus malaccensis, Phragmites australis, and Spartina alterniflora, respectively, in the Min River estuary of southeast China. The mean Reco across tidal stages and vegetation types exhibited strong temporal variations, and the Q10 value for Reco was higher in the warm months than in the cold months. The mean annual Reco was negatively correlated with electrical conductivity and soil water content, but positively correlated with both tidal water level and soil pH (P < 0.05). On the other hand, the seasonal variation in Reco and Q10 was largely driven by the thermal regimes and soil salinity. Also, we found that the mean Reco and Qs10 value were both relatively higher when the site was exposed before tidal inundation, as compared to that after tidal inundation for all the vegetation types studied (P > 0.05). Overall, the C. malacensis and S. alterniflora stands had the highest and lowest average rates of Reco, respectively, while the mean Qs10 values were lower in the Phragmites australis stand than the other two vegetation types. Our findings point to the need of strengthening the in situ measurements of gas fluxes at multiple time scales in order to develop a better understanding of the response of Reco to changing environmental conditions in the subtropical coastal wetlands. Our results also reiterate the importance of considering the influence of vegetation types in characterizing the magnitude and temperature sensitivity of Reco in estuarine tidal marshes for predicting ecosystem responses to future global change.

Unrest at the Nevados de Chillán volcanic complex: a failed or yet to unfold magmatic eruption?

Resuming erupting activity at volcanoes that have been long quiescent poses a significant challenge to hazard assessment, as it require assessment of whether the change in activity is an isolated event or the beginning of a new eruptive sequence. Such inception is often poorly characterised as quiescent volcanoes tend to be poorly equipped and not extensively monitored, especially with respect to gas geochemistry. Here, we report gas composition and flux measurements from a newly opened vent at the very onset of eruptive activity at the Nevados de Chillán volcanic complex (Chile) in January-February 2016. The molar proportions of H2O, CO2, SO2, H2S and H2 gases are found to be 98.4, 0.97, 0.11, 0.01 and 0.5 mol% respectively. The mean SO2 flux recorded in early February 2016 during periods of eruptive discharge amounts to 0.4-0.6 kg s-1. Our results indicate that the new vent opening was propelled by magmatic gases, triggering repeated eruptions. Ash particles ejected by the first blast of 8 January are dominated by lithic fragments of dacitic composition. By contrast the ash ejected in a subsequent eruption contains both lithic fragments of dense dacite, and a fresher, sparsely vesicular material of basaltic andesite composition. By October 2017 the ejected ash is back to being dominated by the dense dacitic lithic material. Together with the seismic and deformation record, these observations point to the explosive activity resulting from a small intrusion of basaltic to andesitic magma at shallow level. The fate of this magma, whether stalling or eventually triggering a magmatic eruption, remains to be seen, but current observations suggest the former is most likely.

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

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

Activity and diversity of methane-oxidizing bacteria along a Norwegian sub-Arctic glacier forefield.

Methane (CH4) is one of the most abundant greenhouse gases in the atmosphere and identification of its sources and sinks is crucial for the reliability of climate model outputs. Although CH4 production and consumption rates have been reported from a broad spectrum of environments, data obtained from glacier forefields are restricted to a few locations. We report the activities of methanotrophic communities and their diversity along a chronosequence in front of a sub-Arctic glacier using high-throughput sequencing and gas flux measurements. CH4 oxidation rates were measured in the field throughout the growing season during three sampling times at eight different sampling points in combination with laboratory incubation experiments. The overall results showed that the methanotrophic community had similar trends of increased CH4 consumption and increased abundance as a function of soil development and time of year. Sequencing results revealed that the methanotrophic community was dominated by a few OTUs and that a short-term increase in CH4 concentration, as performed in the field measurements, altered slightly the relative abundance of the OTUs.

Portable Automation of Static Chamber Sample Collection for Quantifying Soil Gas Flux.

Quantification of soil gas flux using the static chamber method is labor intensive. The number of chambers that can be sampled is limited by the spacing between chambers and the availability of trained research technicians. An automated system for collecting gas samples from chambers in the field would eliminate the need for personnel to return to the chamber during a flux measurement period and would allow a single technician to sample multiple chambers simultaneously. This study describes hamber utomated ampling quipment (Flux) to collect and store chamber headspace gas samples at assigned time points for the measurement of soil gas flux. The FluxCASE design and operation is described, and the accuracy and precision of the FluxCASE system is evaluated. In laboratory measurements of nitrous oxide (NO), carbon dioxide (CO), and methane (CH) concentrations of a standardized gas mixture, coefficients of variation associated with automated and manual sample collection were comparable, indicating no loss of precision. In the field, soil gas fluxes measured from FluxCASEs were in agreement with manual sampling for both NO and CO. Slopes of regression equations were 1.01 for CO and 0.97 for NO. The 95% confidence limits of the slopes of the regression lines included the value of one, indicating no bias. Additionally, an expense analysis found a cost recovery ranging from 0.6 to 2.2 yr. Implementing the FluxCASE system is an alternative to improve the efficiency of the static chamber method for measuring soil gas flux while maintaining the accuracy and precision of manual sampling.

Fluxpart: Open source software for partitioning carbon dioxide and water vapor fluxes

The eddy covariance method is regularly used for measuring gas fluxes over agricultural fields and natural ecosystems. For many applications, it is desirable to partition the measured fluxes into constitutive components: the water vapor flux into transpiration and direct evaporation components, and the carbon dioxide flux into photosynthesis and respiration components. The flux variance similarity (FVS) partitioning method is based on flux variance similarity relationships and correlation analyses of high-frequency eddy covariance data (Scanlon and Sahu, 2008; Scanlon and Kustas, 2010, 2012). The FVS method is relatively complex computationally, and that complexity has likely been an impediment to greater use and testing of the procedure. In this work, we present a new algebraic solution to the key computational task in the partitioning algorithm, which significantly simplifies the FVS method. We also introduce Fluxpart, a free and open source Python 3 module that implements the FVS partitioning procedure. Example flux partitioning calculations are presented.

Landscape topography structures the soil microbiome in arctic polygonal tundra

In the Arctic, environmental factors governing microbial degradation of soil carbon (C) in active layer and permafrost are poorly understood. Here we determined the functional potential of soil microbiomes horizontally and vertically across a cryoperturbed polygonal landscape in Alaska. With comparative metagenomics, genome binning of novel microbes, and gas flux measurements we show that microbial greenhouse gas (GHG) production is strongly correlated to landscape topography. Active layer and permafrost harbor contrasting microbiomes, with increasing amounts of Actinobacteria correlating with decreasing soil C in permafrost. While microbial functions such as fermentation and methanogenesis were dominant in wetter polygons, in drier polygons genes for C mineralization and CH4 oxidation were abundant. The active layer microbiome was poised to assimilate N and not to release N2O, reflecting low N2O flux measurements. These results provide mechanistic links of microbial metabolism to GHG fluxes that are needed for the refinement of model predictions.

Remote sensing of methane and nitrous oxide fluxes from waste incineration

Incomplete combustion processes lead to the formation of many gaseous byproducts that can be challenging to monitor in flue gas released via chimneys. This study presents ground-based remote sensing approaches to make greenhouse gas (GHG) flux measurements of methane (CH4) and nitrous oxide (N2O) from a waste incineration chimney at distances of 150–200 m. The study found emission of N2O (corresponding to 30–40 t yr−1), which is a consequence of adding the reduction agent urea to decrease NOX emissions due to NOX regulation; a procedure that instead increases N2O emissions (which is approximately 300 times more potent as a GHG than CO2 on a 100-year time scale). CH4 emissions of 7–11 t yr−1 was also detected from the studied chimney despite the usage of a high incineration temperature. For this particular plant, local knowledge is high and emission estimates at corresponding levels have been reported previously. However, emissions of CH4 are often not included in GHG emission inventories for waste incineration. This study highlights the importance of monitoring combustion processes, and shows the possibility of surveying CH4 and N2O emissions from waste incineration at distances of several hundred meters.

Effects of storage time and temperature on greenhouse gas samples in Exetainer vials with chlorobutyl septa caps

Measurement of greenhouse gas (GHG) flux using static chamber methods typically occurs immediately following sample collection. However, situations may arise requiring sample storage prior to analysis by gas chromatography. The objective of this study was to determine effects of storage time and temperature on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations in vials containing “low” and “high” concentrations of certified standards. Samples were stored for 3, 7, 14, 28, and 84 days at four storage temperatures: room temperature, 25?°C, 4?°C, and -10?°C. Results indicated low and high concentration standards were not impacted by sample storage up to 28 days at any storage temperature. After 84 days, CO2 concentrations were 0.6–14.4% lower than expected while CH4 concentrations were up to 22% greater than expected. Results from future studies will allow for further refinement of scientifically supported guidance regarding appropriate storage temperature and time of GHG samples.•Few studies have examined impacts of storage time and temperature on GHG samples retained in traditional septa-capped vials.•Effects of storage time and temperature on GHG samples were examined.•Based on this study, GHG samples can be stored for up to 28 days at temperatures ranging from -10?°C to 25?°C.

Maximizing the information obtained from chamber-based greenhouse gas exchange measurements in remote areas

Measurements of greenhouse gas (GHG) fluxes, particularly methane (CH4) and nitrous oxide (N2O) in mountain ecosystems are scarce due to the complexity and unpredictable behavior of these gases, in addition to the remoteness of these ecosystems. In this context, we measured CO2, CH4, and N2O fluxes in four semi-natural pastures in the Pyrenees to investigate their magnitude and range of variability. Our interest was to study GHG phenomena at the patch-level, therefore we chose to measure the gas-exchange using a combination of a gas analyzer and manual chambers. The analyzer used is a photoacoustic field gas-monitor that allows multi-gas instantaneous measurements. After implementing quality control and corrections, data was of variable quality. We tackled this by categorizing data as to providing quantitative or only qualitative information:•50% and 59% of all CH4 and N2O data, respectively, provided quantitative information above the detection limit.•We chose not to discard data providing only qualitative information, because they identify highest- and lowest-flux peak periods and indicate the variability of the fluxes, along different altitudes and under different climatic conditions.•We chose not to give fluxes below detection limit a quantitative value but to acknowledge them as values identifying periods with low fluxes.

Alternate wetting and drying reduces methane emission from a rice paddy in Central Java, Indonesia without yield loss

ABSTRACTWater regimes play a central role in regulating methane (CH4) and nitrous oxide (N2O) emissions from irrigated rice field. Alternate wetting and drying (AWD) is a possible option, but there is limited information on its feasibility under local environmental conditions, especially for tropical region. We therefore carried out a 3-year experiment in a paddy field in Central Java, Indonesia to investigate the feasibility of AWD in terms of rice productivity, greenhouse gas (GHG) emission, and water use both in wet and dry seasons (WS and DS). The treatments of water management were (1) continuous flooding (CF), (2) flooding every when surface water level naturally declines to 15 cm below the soil surface (AWD), and (3) site-specific AWD with different criteria of soil drying (AWDS) established to find out the optimum for GHG emission reduction. Gas flux measurement was conducted by a static closed chamber method. Rice growth was generally normal and the grain yield did not significantly differ among the three treatments both in WS and DS. AWD and AWDS significantly reduced the total water use (irrigation + rainfall) as compared to CF. As expected, the seasonal total CH4 emission was significantly reduced by AWD and AWDS. On average, the CH4 emissions under AWD and AWDS were 35 and 38%, respectively, smaller than those under CF. It should be noted that AWD and AWDS were effective even in WS due partly to the field location on inland, upland area that facilitates the drainage. The seasonal total N2O emission did not significantly differ among the treatments. The results indicate that AWD is a promising option to reduce GHG emission, as well as water use without sacrificing rice productivity in this field.

Uncertainty analysis of gas flux measurements at air–water interface using floating chambers

Floating chambers are widely used to estimate gas fluxes at the air–water interface of surface waters especially to assess greenhouse gas emissions from manmade lakes and reservoirs. The fluxes measured by the chamber method, however, can be significantly biased, as the chamber itself is an intrusive gas flux monitoring method based on measuring gradient changes within the chamber, which are very sensitive to turbulent transport properties at the interface. The relevant parameters are: (i) the measurement time, (ii) the volume to area ratio, (iii) the gas transfer velocity, and (iv) the gas solubility. In this paper we perform an analytical estimation of the uncertainties associated to interferences of the chamber on the flux measurements. We showed that the dominating overestimation factor is driven by artificially-enhanced turbulence due to the chamber deployment which explains the heterogeneous experimental results in literature. We proposed a correction method to reduce uncertainties in gas estimatives and will allow compare measurements with different chamber designs.

Long-term grazing effects on soil-atmosphere exchanges of CO2, CH4 and N2O at different grasslands in Inner Mongolia: A soil core study

Regional greenhouse gas (GHG) budgets in vast grasslands may be changing due to overgrazing and grassland types. However, the comprehensive effects of grazing patterns, environmental factors and grassland types on soil carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) exchanges have been poorly studied. This study investigates the effects of long-term grazing on the soil-atmosphere exchanges of CO 2 , CH 4 and N 2 O in important processes within different grasslands in Inner Mongolia, China. Using manual static chamber and gas chromatography, we measured the fluxes of CO 2 , CH 4 and N 2 O from intact soil cores of paired grazed/ungrazed sites collected from two typical steppes (S tipa grandis and Leymus chinensis ): one wetland in a flood plain and one desert steppe in the region of the Xilin River catchment, Inner Mongolia. Soil gas flux and concentration measurements were conducted in four simulated conditions ( i.e. , drought, dry-wet, intense rainfall and freeze-thaw), which represent important processes in annual GHG exchanges. Extreme drought significantly inhibited CO 2 and N 2 O emissions in all plots but did not change the CH 4 uptake by typical steppes. Dry-wet transition and intense rainfall could remarkably promote soil CO 2 emission pulses at different types, significantly decrease CH 4 uptake by typical steppes, and arouse N 2 O emission pulses at all plots with different times of occurrence. During the freeze-thaw simulation, temperature-induced soil CO 2 emission and CH 4 uptake/emission presented a clear alternative variation, while soil thaw only slightly increased (<15 μg N m −2 h −1 ) in the steppes and sand dunes and was significantly higher in the wetland (11–96 μg N m −2 h −1 ). Long-term grazing significantly inhibited soil respiration rates at all grassland types, significantly decreased CH 4 uptake by the Leymus chinensis steppes, and did not show significant influence on N 2 O emission due to large spatial variations for all types. Compared to the ungrazed Leymus steppes, Stipa steppes, sand dune and wetland, continuously grazed sites were significantly reduced by 22%, 38%, 48% and 47% in total GHG emissions, respectively. Our results indicate that the potential of the steppe soil CH 4 sink function can be offset by N 2 O emission, especially in over-grazed plots. Furthermore, N 2 O emissions should be considered in wetland rangelands with significantly higher N 2 O emission potential (range: 0–343 μg N m −2 h −1 ) more than steppes (range: 0–132 μg N m −2 h −1 ) and sand dunes (range: 0–49 μg N m −2 h −1 ). Nevertheless, comprehensive evaluation of the grazing effect on ecosystem GHG emissions merits consider in both field observation and incubation experiments because soil properties and environmental factors could be changed by vegetation growth in different grazing practices.

Fluxes of greenhouse gases from incubated soils using different lid-closure times

Different sampling times for greenhouse gas measurements have been proposed in many incubation studies. Little is known about effects of closure time on denitrification and nitrification rates from incubation experiments. The objectives of this study were to analyse greenhouse gas (carbon dioxide, methane and nitrous oxide) production from different soils with different times of lid closure and to assess effects of different activation times (defined as additional pre-incubation periods before incubation experiments) on gas emissions from soils. Forty grams of air-dried soil samples (depth 0–10 cm) were incubated in 125-mL jars at 25°C with the addition of glucose and nitrate. The first experiment measured greenhouse gas fluxes at different lid-closure times (40, 80, 120 and 1440 min). The second experiment assessed the effects of different durations of soil activation (0.7, 1.3, 2 and 24 h) on gas emissions. Both were conducted with a completely randomised design, with three replicates per treatment. Our findings showed closure time &lt;1 h or &gt;2 h may cause an underestimate of greenhouse gas emissions. Lengthening activation times resulted in different emission rates consistent with soil characteristics. To measure gas fluxes based on linear regression would require four or five sampling points and sampling at a 20-min interval over a maximum period of 80 min for estimating gas fluxes from soil. Because pre-incubation time is critical and a driving factor in the measurement of soil-induced gas emissions, a standardised procedure to quantify gas fluxes is needed for application to other soils.

Biochar influences on soil CO2 and CH4 fluxes in response to wetting and drying cycles for a forest soil

Biochar has been the focus of significant research efforts in agriculture, but little research has been conducted in forested ecosystems. Here, we assess CO2 and CH4 fluxes from a forest soil in response to biochar additions using a before-after-control-intervention experimental design. Soil CO2 and CH4 fluxes were measured over a series of wetting cycles by coupling soil mesocosms equipped with auto-chambers to a laser-based spectrometer for high-frequency measurements of gas fluxes and related soil processes. We found that soil CO2 fluxes were higher and CH4 fluxes were less negative (e.g. reduced CH4 uptake) for the biochar-amended soil compared to the no biochar condition. Furthermore, biochar improved soil infiltrability under wet conditions, and enhanced soil moisture levels under dry conditions. Biochar additions shifted the point of maximum soil respiration (i.e. soil CO2 efflux) to a slightly wetter soil moisture level. The point of maximum CH4 uptake was also shifted to a slightly wetter moisture level for soil with biochar. Overall differences in soil gas fluxes were found to be minor compared to the increase in soil carbon resulting from the biochar addition. Biochar may thus contribute to improved forest management through increases to soil carbon stocks and improved soil moisture levels.

The physical characteristics of a CO2 seeping fault: The implications of fracture permeability for carbon capture and storage integrity

To ensure the effective long-term storage of CO2 in candidate geological storage sites, evaluation of potential leakage pathways to the surface should be undertaken. Here we use a series of natural CO2 seeps along a fault in South Africa to assess the controls on CO2 leakage to the surface. Geological mapping and detailed photogrammetry reveals extensive fracturing along the mapped fault trace. Measurements of gas flux and CO2 concentration across the fracture corridor give maximum soil gas measurements of 27% CO2 concentration and a flux of 191gm−2d−1. These measurements along with observations of gas bubbles in streams and travertine cones attest to CO2 migration to the surface. Permeability measurements on the host rock units show that the tillite should act as an impermeable seal to upward CO2 migration. The combined permeability and fracture mapping data indicate that fracture permeability creates the likely pathway for CO2 migration through the low permeability tillite to the surface. Heterogeneity in fracture connectivity and intensity at a range of scales will create local higher permeability pathways along the fracture corridor, although these may seal with time due to fluid-rock interaction. The results have implications for the assessment and choice of geological CO2 storage sites, particularly in the assessment of sub-seismic fracture networks.

Effects of warming and nitrogen fertilization on GHG flux in the permafrost region of an alpine meadow

The limited number of in situ measurements of greenhouse gas (GHG) flux during soil freeze-thaw cycles in permafrost regions limits our ability to accurately predict how the alpine ecosystem carbon sink or source function will vary under future warming and increased nitrogen (N) deposition. An alpine meadow in the permafrost region of the Qinghai-Tibet Plateau was selected, and a simulated warming with N fertilization experiment was carried out to investigate the key GHG fluxes (ecosystem respiration [Re], CH4 and N2O) in the early (EG), mid (MG) and late (LG) growing seasons. The results showed that: (i) warming (4.5 °C) increased the average seasonal Re, CH4 uptake and N2O emission by 73.5%, 65.9% and 431.6%, respectively. N fertilization (4 g N m−2) alone had no significant effect on GHG flux; the interaction of warming and N fertilization enhanced CH4 uptake by 10.3% and N2O emissions by 27.2% than warming, while there was no significant effect on the Re; (ii) the average seasonal fluxes of Re, CH4 and N2O were MG > LG > EG, and Re and CH4 uptake were most sensitive to the soil freezing process instead of soil thawing process; (iii) surface soil temperature was the main driving factor of the Re and CH4 fluxes, and the N2O flux was mainly affected by daily rainfall; (iv) in the growing season, warming increased greenhouse warming potential (GWP) of the alpine meadow by 74.5%, the N fertilization decreased GWP of the warming plots by 13.9% but it was not statistically significant. These results indicate that (i) relative to future climate warming (or permafrost thawing), there could be a hysteresis of GHG flux in the alpine meadow of permafrost region; (ii) under the scenario of climate warming, increasing N deposition has limited impacts on the feedback of GHG flux of the alpine meadow.

Extensive grazing in contrast to mowing is climate-friendly based on the farm-scale greenhouse gas balance

Livestock is both threatened by and contributing to climate change. The contribution of livestock to climate change and greenhouse gas (GHG) emission greatly vary under different management regimes. A number of mitigation options comprise livestock management, although there are a lot of uncertainties as to which management regime to use for a given pedoclimatic and farming system. Therefore, we 1) tested if an extensive cattle livestock farm is a net sink or a net source for GHG (carbon–dioxide, CO2; methane, CH4; nitrous oxide N2O) in Central–Eastern Europe, 2) compared the annual GHG balances between the grazed and mowed treatments of the farm 3) and investigated the role of climate variability in shaping these balances. Net ecosystem exchange of CO2 (NEE) was measured with eddy covariance technique in both the grazed and mowed treatments. Estimations of lateral C fluxes were based on management data. Other GHG fluxes (CH4, N2O) were determined by chamber gas flux measurements technique (in case of soil) and IPCC guidelines (in case of manure decomposition and animal fermentation). Net greenhouse gas balance (NGHG) for the grazed treatment was 228±283g CO2 equivalent m−2year−1 (net sink) and −475±144g CO2 equiv. m−2year−1 (net source) for the mowed treatment. Net source activity at the mowed treatment was due to its higher herbage use intensity compared to the grazed treatment. At the farm scale the system was estimated to be a net sink for NGHG in a year with wet (135g CO2 equiv. m−2year−1), while a net source in years with dry soil moisture conditions (−267±214g CO2 equiv. m−2year−1). We conclude that under a temperate continental climate extended extensive grazing could serve as a potential mitigation of GHG in contrast to mowing. Our study highlights the fact that livestock farming could create a net sink for GHG under proper management regimes.