Variation In Methane Emissions Research Articles

Temporal Variations in Methane Emissions from an Unconventional Well Site.

Studies have aimed to quantify methane emissions associated with the growing natural gas infrastructure. Quantification is completed using direct or indirect methods—both of which typically represent only a snapshot in time. Most studies focused on collecting emissions data from multiple sites to increase sample size, thus combining the effects of geospatial and temporal variability (spatio-temporal variability). However, we examined the temporal variability in methane emissions from a single unconventional well site over the course of nearly 2 years (21 months) by conducting six direct quantification audits. We used a full flow sampling system that quantified methane mass emissions with an uncertainty of ±10%. Results showed significant temporal variation in methane mass emissions ranging from 86.2 to 4102 g/h with a mean of 1371 g/h. Our average emissions rate from this unconventional well pad tended to align with those presented in the literature. The largest contributor to variability in site emissions was the produced water tank which had emissions rates ranging from 17.3 to 3731 g/h. We compared our methane mass emissions with the total production for each audit and showed that relative methane loss rates ranged from 0.002 to 0.088% with a mean of 0.030%, typically lower than reported by the literature, noting that our data excluded well unloadings. We examined natural gas production, water production, and weather conditions for trends. The strongest correlation was between methane emissions and historical water production. Our data shows that even for a single site, a snapshot in time could significantly over-predict (3×) or under-predict (16×) methane emissions as compared to a long-term temporal average.

Abundance, rather than composition, of methane-cycling microbes mainly affects methane emissions from different vegetation soils in the Zoige alpine wetland.

Methane fluxes, which are controlled by methanogens and methanotrophs, vary among wetland vegetation species. In this study, we investigated belowground methanogens and methanotrophs in two soils under two different dominant vegetation species with different methane fluxes in the Zoige wetland, which was slightly but significantly (p ≤ 0.05) higher in soils covered by Carex muliensis than that in soils covered by Eleocharis valleculosa. Real‐time quantitative PCR and Illumina MiSeq sequencing methods were used to elucidate the microbial communities based on the key genes involved in methane production and oxidation. The absolute abundances of methanogens and methanotrophs of samples from C. muliensis were 1.80 ± 0.07 × 106 and 4.03 ± 0.28 × 106 copies g‐soil−1, respectively, and which from E. valleculosa were 3.99 ± 0.19 × 105 and 2.53 ± 0.22 × 106 copies g‐soil−1 , respectively. The t‐test result showed that both the abundance of methanogens and methanotrophs from C. muliensis were significantly higher (p ≤ 0.05) than that of samples from E. valleculosa. However, the diversities and compositions of both methanogens and methanotrophs showed no significant differences (p ≥ 0.05) between vegetation species. The path analysis showed that the microbial abundance had a greater effect than the microbial diversity on methane production potentials and the regression analysis also showed that the methane emissions significantly (p ≤ 0.05) varied with the abundance of methane‐cycling microbes. These findings imply that abundance rather than diversity and composition of a methane‐cycling microbial community is the major contributor to the variations in methane emissions between vegetation types in the Zoige wetland.

Milk fatty acids estimated by mid-infrared spectroscopy and milk yield can predict methane emissions in dairy cows

Ruminant enteric methane emission contributes to global warming. Although breeding low methane-emitting cows appears to be possible through genetic selection, doing so requires methane emission quantification by using elaborate instrumentation (respiration chambers, SF6 technique, GreenFeed) not feasible on a large scale. It has been suggested that milk fatty acids are promising markers of methane production. We hypothesized that methane emission can be predicted from the milk fatty acid concentrations determined by mid-infrared spectroscopy, and the integration of energy-corrected milk yield would improve the prediction. Therefore, we examined relationships between methane emission of cows measured in respiration chambers and milk fatty acids, predicted by mid-infrared spectroscopy, to derive diet-specific and general prediction equations based on milk fatty acid concentrations alone and with the additional consideration of energy-corrected milk yield. Cows were fed diets differing in forage type and linseed supplementation to generate a large variation in both CH4 emission and milk fatty acids. Depending on the diet, equations derived from regression analysis explained 61 to 96% of variation of methane emission, implying the potential of milk fatty acid data predicted by mid-infrared spectroscopy as novel proxy for direct methane emission measurements. When data from all diets were analyzed collectively, the equation with energy-corrected milk yield (CH4 (L/day) = − 1364 + 9.58 × energy-corrected milk yield + 18.5 × saturated fatty acids + 32.4 × C18:0) showed an improved coefficient of determination of cross-validation R2CV = 0.72 compared to an equation without energy-corrected milk yield (R2CV = 0.61). Equations developed for diets supplemented by linseed showed a lower R2CV as compared to diets without linseed (0.39 to 0.58 vs. 0.50 to 0.91). We demonstrate for the first time that milk fatty acid concentrations predicted by mid-infrared spectroscopy together with energy-corrected milk yield can be used to estimate enteric methane emission in dairy cows.

Diurnal variation of methane emission from a paddy field in Brazilian Southeast

ABSTRACT: This study aimed to investigate the diurnal variation of methane (CH4) emission in a flooded-irrigated rice field at different stages of the plant development under tropical climate in three growing seasons, in order to determine the most appropriate time for gas sampling in the Brazilian Southeast region. It aimed also to verify correlations between CH4 flux and air, water and soil temperatures, and solar radiation. The CH4 emissions were measured every 3-hour interval on specific days in different development stages of the flooded rice in the Experiment Station of the Agência Paulista de Tecnologia dos Agronegócios (APTA), Pólo Regional Vale do Paraíba, at Pindamonhangaba, State of São Paulo (22°55’ S, 45°30’ W), Brazil. Different CH4 emission rates were observed among the plant growth stages and also among the growing seasons. The CH4 emission showed high correlation with the soil temperature at 2cm depth. At this depth, the CH4 emission activation energy in response to soil temperature was higher in the stage R2. Emission peaks were observed at afternoon, while lower fluxes were recorded at the early morning. The most appropriate local time for gas sampling was estimated at 12:11:15a.m.±01:14:16 and 09:05:49p.m.±01:29:04.

Small spatial variability in methane emission measured from a wet patterned boreal bog

Abstract. We measured methane fluxes of a patterned bog situated in Siikaneva in southern Finland from six different plant community types in three growing seasons (2012–2014) using the static chamber method with chamber exposure of 35 min. A mixed-effects model was applied to quantify the effect of the controlling factors on the methane flux. The plant community types differed from each other in their water level, species composition, total leaf area (LAITOT) and leaf area of aerenchymatous plant species (LAIAER). Methane emissions ranged from −309 to 1254 mg m−2 d−1. Although methane fluxes increased with increasing peat temperature, LAITOT and LAIAER, they had no correlation with water table or with plant community type. The only exception was higher fluxes from hummocks and high lawns than from high hummocks and bare peat surfaces in 2013 and from bare peat surfaces than from high hummocks in 2014. Chamber fluxes upscaled to ecosystem level for the peak season were of the same magnitude as the fluxes measured with the eddy covariance (EC) technique. In 2012 and in August 2014 there was a good agreement between the two methods; in 2013 and in July 2014, the chamber fluxes were higher than the EC fluxes. Net fluxes to soil, indicating higher methane oxidation than production, were detected every year and in all community types. Our results underline the importance of both LAIAER and LAITOT in controlling methane fluxes and indicate the need for automatized chambers to reliably capture localized events to support the more robust EC method.

Genetic background of methane emission by Dutch Holstein Friesian cows measured with infrared sensors in automatic milking systems

International environmental agreements have led to the need to reduce methane emission by dairy cows. Reduction could be achieved through selective breeding. The aim of this study was to quantify the genetic variation of methane emission by Dutch Holstein Friesian cows measured using infrared sensors installed in automatic milking systems (AMS). Measurements of CH4 and CO2 on 1,508 Dutch Holstein Friesian cows located on 11 commercial dairy farms were available. Phenotypes per AMS visit were the mean of CH4, mean of CO2, mean of CH4 divided by mean of CO2, and their log10-transformations. The repeatabilities of the log10-transformated methane phenotypes were 0.27 for CH4, 0.31 for CO2, and 0.14 for the ratio. The log10-transformated heritabilities of these phenotypes were 0.11 for CH4, 0.12 for CO2, and 0.03 for the ratio. These results indicate that measurements taken using infrared sensors in AMS are repeatable and heritable and, thus, could be used for selection for lower CH4 emission. Furthermore, it is important to account for farm, AMS, day of measurement, time of day, and lactation stage when estimating genetic parameters for methane phenotypes. Selection based on log10-transformated CH4 instead of the ratio would be expected to give a greater reduction of CH4 emission by dairy cows.

Aspects of digestive function in sheep related to phenotypic variation in methane emissions

Ruminant livestock contribute to atmospheric methane (CH4) from enteric microbial fermentation of feed in the reticulo-rumen. Our research aimed to increase understanding of how digestive characteristics and rumen anatomy of the host animal contribute to variation in CH4 emissions between individual sheep. In total, 64 ewes were used in an incomplete block experiment with four experimental test periods (blocks). Ewes were chosen to represent the diversity of phenotypic variation in CH4 emissions: there were at least 10 offspring from each of four sires and a range of liveweights. Throughout the experiment, the ewes were fed equal parts of lucerne and oaten chaff, twice daily, at 1.5 times the maintenance requirements. Daily CH4 emission (g/day) increased significantly (P < 0.001) with an increasing dry-matter intake (DMI) and reticulo-rumen volume (P < 0.001). Lower methane yield (g CH4/kg DMI) was associated with shorter mean retention times of liquid (r = 0.59; P < 0.05) and particle (r = 0.63; P < 0.05) phases of the digesta in the rumen. Significant between sire variation was observed in CH4 emissions and in rumen volume (P = 0.02), the masses of liquids (P = 0.009) and particles (P < 0.03) in the rumen and the proportion of gas in the dorsal sac of the rumen (P = 0.008). The best predictors of variation in CH4 emissions due to the host were DMI, CO2 emissions, rumen volume, liveweight, mean retention time of particles in the rumen, dorsal papillae density and the proportion of liquid in the contents of the rumen compartments.

Modelling the Diurnal Variations of Methane Emissions from the Cyperus malaccensis Tidal Marsh in the Minjiang River Estuary

Tidal marshes are important sources of atmospheric methane; however, the processes and mechanisms of diurnal methane flux variations in tidal marshes remain unclear. In this study, we modified the Walter model to simulate diurnal variations of methane fluxes in the Cyperus malaccensis tidal marsh in the Minjiang River Estuary. The sediment environmental variables, relative humidity (RH), and the tide level were considered in the modified model; the explicit difference scheme was applied for model calculation. Our simulated and observed results indicate that the methane fluxes are higher in non-inundation periods and lower in inundation periods, higher during the day and lower at night. Moreover, our simulation suggests that plant-mediated transport and ebullition are dominant pathways for methane emissions, and the diurnal variation patterns of methane fluxes are directly regulated by the tide level, sediment temperature, and RH. The model sensitivity tests suggest that methane fluxes are significantly influenced by the maximum potential methane production rate and various environmental variables. The model comparison indicates that our modifications have significantly improved the performance of the model in simulating diurnal variations of methane emissions in the C. malaccensis tidal marsh.

Atmospheric modeling to assess wind dependence in tracer dilution method measurements of landfill methane emissions

The short-term temporal variability of landfill methane emissions is not well understood due to uncertainty in measurement methods. Significant variability is seen over short-term measurement campaigns with the tracer dilution method (TDM), but this variability may be due in part to measurement error rather than fluctuations in the actual landfill emissions. In this study, landfill methane emissions and TDM−measured emissions are simulated over a real landfill in Delaware, USA using the Weather Research and Forecasting model (WRF) for two emissions scenarios. In the steady emissions scenario, a constant landfill emissions rate is prescribed at each model grid point on the surface of the landfill. In the unsteady emissions scenario, emissions are calculated at each time step as a function of the local surface wind speed, resulting in variable emissions over each 1.5-h measurement period. The simulation output is used to assess the standard deviation and percent error of the TDM−measured emissions. Eight measurement periods are simulated over two different days to look at different conditions. Results show that standard deviation of the TDM- measured emissions does not increase significantly from the steady emissions simulations to the unsteady emissions scenarios, indicating that the TDM may have inherent errors in its prediction of emissions fluctuations. Results also show that TDM error does not increase significantly from the steady to the unsteady emissions simulations. This indicates that introducing variability to the landfill emissions does not increase errors in the TDM at this site. Across all simulations, TDM errors range from −15% to 43%, consistent with the range of errors seen in previous TDM studies. Simulations indicate diurnal variations of methane emissions when wind effects are significant, which may be important when developing daily and annual emissions estimates from limited field data.

Simulation of macerals effects on methane emission during gas drainage in coal mines

The methane found in coal is regarded as one of the clean energy resources. Methane forms inside coal beds according to geological conditions through coalification. The lifecycle of coalification and source of coal formation directly affect macerals. Coal is classified based on its maceral content. In this study, firstly macerals were identified in coal samples from two different mines. Then, the permeability of each sample was measured. Subsequently, parameters obtained from experiments were introduced as input numerical data into COMSOL Multiphysics commercial software. This study was intended to measure the impact of macerals on the level of methane emission in an attempt to remove gas from coal beds. It was found that vitrinite levels in Tabas and Shahrood mines coal were 81.34% and 69.31% respectively. The methane emission rate was 0.00269m/s in Tabas coal and 0.00258m/s in Shahrood coal, a variation of 12% increase in vitrinite. The increase in vitrinite content in Tabas Mine has contributed to the rate of emission increase by about 0.00011m/s or 0.66m3/min. This variation in methane emission was due to the maceral content.

Remotely sensed MODIS wetland components for assessing the variability of methane emissions in Indian tropical/subtropical wetlands

Temperature and area fluctuations in wetlands greatly influence its various physico-chemical characteristics, nutrients dynamic, rates of biomass generation and decomposition, floral and faunal composition which in turn influence methane (CH4) emission rates. In view of this, the present study attempts to up-scale point CH4 flux from the wetlands of Uttar Pradesh (UP) by modifying two-factor empirical process based CH4 emission model for tropical wetlands by incorporating MODIS derived wetland components viz. wetland areal extent and corresponding temperature factors (Ft). This study further focuses on the utility of remotely sensed temperature response of CH4 emission in terms of Ft. Ft is generated using MODIS land surface temperature products and provides an important semi-empirical input for up-scaling CH4 emissions in wetlands. Results reveal that annual mean Ft values for UP wetlands vary from 0.69 (2010–2011) to 0.71(2011–2012). The total estimated area-wise CH4 emissions from the wetlands of UP varies from 66.47Ggyr−1with wetland areal extent and Ft value of 2564.04km2 and 0.69 respectively in 2010–2011 to 88.39Ggyr−1with wetland areal extent and Ft value of 2720.16km2 and 0.71 respectively in 2011–2012. Temporal analysis of estimated CH4 emissions showed that in monsoon season estimated CH4 emissions are more sensitive to wetland areal extent while in summer season sensitivity of estimated CH4 emissions is chiefly controlled by augmented methanogenic activities at high wetland surface temperatures.

Variability in methane emissions from West Siberia's shallow boreal lakes on a regional scale and its environmental controls

Abstract. Small lakes represent an important source of atmospheric CH4 from northern wetlands. However, spatiotemporal variations in flux magnitudes and the lack of knowledge about their main environmental controls contribute large uncertainty into the global CH4 budget. In this study, we measured methane fluxes from small lakes using chambers and bubble traps. Field investigations were carried out in July–August 2014 within the West Siberian middle and southern taiga zones. The average and median of measured methane chamber fluxes were 0.32 and 0.30 mgCH4 m−2 h−1 for middle taiga lakes and 8.6 and 4.1 mgCH4 m−2 h−1 for southern taiga lakes, respectively. Pronounced flux variability was found during measurements on individual lakes, between individual lakes and between zones. To analyze these differences and the influences of environmental controls, we developed a new dynamic process-based model. It shows good performance with emission rates from the southern taiga lakes and poor performance for individual lakes in the middle taiga region. The model shows that, in addition to well-known controls such as temperature, pH and lake depth, there are significant variations in the maximal methane production potential between these climatic zones. In addition, the model shows that variations in gas-filled pore space in lake sediments are capable of controlling the total methane emissions from individual lakes. The CH4 emissions exhibited distinct zonal differences not only in absolute values but also in their probability density functions: the middle taiga lake fluxes were best described by a lognormal distribution while the southern taiga lakes followed a power-law distribution. The latter suggests applicability of self-organized criticality theory for methane emissions from the southern taiga zone, which could help to explain the strong variability within individual lakes.

Spatiotemporal Variability of Methane Emissions at Oil and Natural Gas Operations in the Eagle Ford Basin.

Methane emissions from oil and gas facilities can exhibit operation-dependent temporal variability; however, this variability has yet to be fully characterized. A field campaign was conducted in June 2014 in the Eagle Ford basin, Texas, to examine spatiotemporal variability of methane emissions using four methods. Clusters of methane-emitting sources were estimated from 14 aerial surveys of two ("East" or "West") 35 × 35 km grids, two aircraft-based mass balance methods measured emissions repeatedly at five gathering facilities and three flares, and emitting equipment source-types were identified via helicopter-based infrared camera at 13 production and gathering facilities. Significant daily variability was observed in the location, number (East: 44 ± 20% relative standard deviation (RSD), N = 7; West: 37 ± 30% RSD, N = 7), and emission rates (36% of repeat measurements deviate from mean emissions by at least ±50%) of clusters of emitting sources. Emission rates of high emitters varied from 150-250 to 880-1470 kg/h and regional aggregate emissions of large sources (>15 kg/h) varied up to a factor of ∼3 between surveys. The aircraft-based mass balance results revealed comparable variability. Equipment source-type changed between surveys and alterations in operational-mode significantly influenced emissions. Results indicate that understanding temporal emission variability will promote improved mitigation strategies and additional analysis is needed to fully characterize its causes.

Temporal variations in methane emissions from emergent aquatic macrophytes in two boreonemoral lakes.

Methane (CH4) emissions via emergent aquatic macrophytes can contribute substantially to the global CH4 balance. We addressed temporal variability in CH4 flux by using the static chamber approach to quantify fluxes from plots dominated by two species considered to differ in flux transport mechanisms (Phragmites australis, Carex rostrata). Temporal variability in daily mean emissions from early June to early October was substantial. The variable that best explained this variation was air temperature. Regular and consistent diel changes were absent and therefore less relevant to include when estimating or modelling CH4 emissions. Methane emissions per m2 from nearby plots were similar for Phragmites australis and Carex rostrata indicating that CH4 production in the system influenced emissions more than the species identity. This study indicates that previously observed diel patterns and species-effects on emissions require further evaluation to support improved local and regional CH4 flux assessments.

Spatial variations of methane emission in a large shallow eutrophic lake in subtropical climate

Subtropical lakes are an important source of atmospheric methane (CH4). This study aims to investigate spatial variations of the CH4 flux in Lake Taihu, a large (area 2400 km2) and shallow (mean depth 1.9 m) eutrophic lake in Eastern China. The lake exhibited high spatial variations in pollution level, macrophyte vegetation abundance, and algal growth. We measured the diffusion CH4 flux via the transfer coefficient method across the whole lake. In addition, data obtained with the flux-gradient and the eddy-covariance methods were used in conjunction with the data on the diffusion flux to estimate the contribution by ebullition. Results from three years’ measurements indicate high spatial variabilities in the diffusion CH4 flux. The spatial pattern of the diffusion CH4 emission was correlated with water clarity, and dissolved oxygen concentration, and with the spatial distributions of algal and submerged vegetation. In comparison to the transfer coefficient method, the eddy covariance and the flux-gradient method observed a lake CH4 flux that was 3.39 ± 0.58 (mean ± one standard deviation) and 1.95 ± 0.36 times higher in an open-water eutrophic zone and in a habitat of submerged macrophytes, respectively. The result implied an average of 71% and 49% ebullition contribution to the total CH4 flux in the two zones. The annual mean diffusion CH4 flux of the whole lake was 0.54 ± 0.30 g m-2 year-1. Our CH4 emission data suggest that the average CH4 emission reported previously for lakes in Eastern China was overestimated.

Interannual variation in methane emissions from tropical wetlands triggered by repeated El Niño Southern Oscillation.

Methane (CH4 ) emissions from tropical wetlands contribute 60%-80% of global natural wetland CH4 emissions. Decreased wetland CH4 emissions can act as a negative feedback mechanism for future climate warming and vice versa. The impact of the El Niño-Southern Oscillation (ENSO) on CH4 emissions from wetlands remains poorly quantified at both regional and global scales, and El Niño events are expected to become more severe based on climate models' projections. We use a process-based model of global wetland CH4 emissions to investigate the impacts of the ENSO on CH4 emissions in tropical wetlands for the period from 1950 to 2012. The results show that CH4 emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Niño periods and with positive anomalies occurring during La Niña periods. An approximately 8-month time lag was detected between tropical wetland CH4 emissions and ENSO events, which was caused by the combined time lag effects of ENSO events on precipitation and temperature over tropical wetlands. The ENSO can explain 49% of interannual variations for tropical wetland CH4 emissions. Furthermore, relative to neutral years, changes in temperature have much stronger effects on tropical wetland CH4 emissions than the changes in precipitation during ENSO periods. The occurrence of several El Niño events contributed to a lower decadal mean growth rate in atmospheric CH4 concentrations throughout the 1980s and 1990s and to stable atmospheric CH4 concentrations from 1999 to 2006, resulting in negative feedback to global warming.

Diurnal variations in methane emissions from West Siberia peatlands in summer

New data on the diurnal variability of methane emission in summer (2013-2014) from West Siberia peatland ecosystems are presented. It is demonstrated that diurnal variations in methane emission differ much depending on a peatland ecosystem under study. Diurnal variations in methane emission in the fens and hollows of the ridge-hollow complex (RHC) are revealed as well as their reproducibility in 2013-2014. The maximum emission is registered in the daytime, and the minimum is observed at night. There is no diurnal variation in methane emission in ryams (pine bogs) and ridges of RHC. It is revealed that in the upper layer of peat (at the depth up to 10 cm for hollows and at the depth of 2 and 5 cm for fens) the contribution of temperature variability to methane emission variations in fens and hollows is 15-20%. The multiple linear regression with peat temperature at several depths allows explaining 44-54% of the variability of methane flux from peatlands. No significant correlation between methane fluxes and the temperature of peat and air was identified in the diurnal cycle in ryams and ridges.

Growing season methane emissions from a permafrost peatland of northeast China: Observations using open-path eddy covariance method

The mid-high latitude permafrost peatlands in the Northern Hemisphere is a major natural source of methane (CH4) to the atmosphere. Ecosystem scale CH4 emissions from a typical permafrost peatland in the Great Hing'an Mountains were observed during the growing season of 2014 and 2015 using the open-path eddy covariance method. Relevant environmental factors such as temperature and precipitation were also collected. There was a clear diurnal variation in methane emissions in the second half of each growing season, with significantly higher emission rates in the wet sector of study area. The daily CH4 exchange ranged from 1.8 mg CH4 m−2 d−1 to 40.2 mg CH4 m−2 d−1 in 2014 and ranged from −3.9 to 15.0 mg CH4 m−2 d−1 in 2015. There were no peaks of CH4 fluxes during the spring thawing period. However, large peaks of CH4 emission were found in the second half of both growing seasons. The CH4 emission after Jul 25th accounted for 77.9% of total growing season emission in 2014 and 85.9% in 2015. The total CH4 emission during the growing season of 2014 and 2015 was approximately 1.52 g CH4 m−2 and 0.71 g CH4 m−2, respectively. CH4 fluxes during the growing seasons were significantly correlated with thawing depth (R2 = 0.71, P < 0.01) and soil temperatures (R2 = 0.75, P < 0.01) at 40 cm depth. An empirical equation using these two major variables was modified to estimate growing season CH4 emissions in permafrost peatlands. Our multiyear observations indicate that the time-lagged volume of precipitation during the growing season is a key factor in interpreting locally inter-annual variations in CH4 emissions. Our results suggested that the low temperature in the deep soil layers effectively restricts methane production and emission rates; these conditions may create significant positive feedback under global climate change.

Effects of increased temperatures and rice straw incorporation on methane and nitrous oxide emissions in a greenhouse experiment with rice

We investigated the effect of increased temperatures of water and soil, together with the incorporation of rice straw, on emissions of methane (CH4) and nitrous oxide (N2O), and the daily variation in CH4 emissions. Three temperature treatments (floodwater temperature), ambient, ambient +2°C and ambient +4°C, and two amounts of rice straw (0 and 6 t ha−1) were arranged in a randomized complete block design with four replications. The emissions of CH4 and N2O and the soil's redox potential (Eh) were measured weekly for two crop cycles. Daily variation in CH4 emission rates was measured with and without rice straw incorporation in planted and unplanted soil (with no warming treatments) during four growth stages of the crop. Methane emissions increased by as much as 91% with increasing amounts of water and soil temperature (+2 and +4°C), up to 34–35°C. Increases in temperature (+2 and +4°C above ambient) above 34–35°C decreased emissions by 30–36%. A decrease in soil Eh to &lt; −100 mV and in CH4 emissions was observed earlier in the pots containing rice straw than in those without straw. Methane emissions varied daily; they were larger from 11:00 to 14:00 hours, particularly in unplanted soil. They showed positive correlations with the temperatures of both soil and air. In contrast, N2O emissions were negligible throughout the growing season. The emissions of CH4 evidently depend on the background temperature range; in our experiment, CH4 emissions increased up to 34°C and then they decreased above that.Highlights:GHG emissions were measured from flooded rice soil under elevated temperatures. Temperature, straw incorporation and rice plants affected daily variation in methane emissions. An increase in temperature increased methane emission by up to 91%. Increased temperature decreased methane emissions when background temperature was above 34–35°C.

Temporal variation in methane emissions in a shallow lake at a southern mid latitude during high and low rainfall periods.

The global methane (CH4) emission of lakes is estimated at between 6 and 16% of total natural CH4 emissions. However, these values have a high uncertainty due to the wide variety of lakes with important differences in their morphological, biological, and physicochemical parameters and the relatively scarse data from southern mid-latitude lakes. For these reasons, we studied CH4 fluxes and CH4 dissolved in water in a typical shallow lake in the Pampean Wetland, Argentina, during four periods of consecutive years (April 2011-March 2015) preceded by different rainfall conditions. Other water physicochemical parameters were measured and meteorological data were reported. We identified three different states of the lake throughout the study as the result of the irregular alternation between high and low rainfall periods, with similar water temperature values but with important variations in dissolved oxygen, chemical oxygen demand, water turbidity, electric conductivity, and water level. As a consequence, marked seasonal and interannual variations occurred in CH4 dissolved in water and CH4 fluxes from the lake. These temporal variations were best reflected by water temperature and depth of the Secchi disk, as a water turbidity estimation, which had a significant double correlation with CH4 dissolved in water. The mean CH4 fluxes values were 0.22 and 4.09mg/m2/h for periods with low and high water turbidity, respectively. This work suggests that water temperature and turbidity measurements could serve as indicator parameters of the state of the lake and, therefore, of its behavior as either a CH4 source or sink.