Total CH4 Flux Research Articles

Pengembangan Model Denitrification Decomposition (DNDC) Untuk Pendugaan Emisi Gas Metana (CH4) Dari Lahan Padi Sawah

Cultivated paddy fields that applied in Indonesia currently produces high emissions of greenhouse gases (GHG), particularly methane gas (CH4). This research aimed to analyze CH4 gas emission in various water management, and to develop DNDC model in predicting CH4 gas emission. This research was conducted from January to May 2018, located at field laboratory of Departement of Civil and Environmental Engineering. The research was conducted by three water regimes i.e., continuously flooded (RT) for conventional rice farming, wet regime (RB), and dry regime (RK) for system of rice intensification (SRI). The highest total methane (CH4) flux was 48.74 kg/ha on RT, on RB was 3.59 kg/ha and on RK -5.40 kg/ha. DNDC model needed data inputs of climate, soil physics, vegetation and anthropogenic activities. The result of the DNDC model showed that the highest total CH4 flux was 44.44 kg/ha on RT, on RB was 17.88 kg/ha and on RK was 0.02 kg/ha. The result, of total actual of CH4 gas flux was compared with DNDC model and got the coefficient of determination (R2) values 0.93, so the model could be used to predict total CH4 gas emission.Keywords: DNDC, methane gas, paddy field, water regime.

Analysis of atmospheric CH<sub>4</sub> in Canadian Arctic and estimation of the regional CH<sub>4</sub> fluxes

Abstract. The Canadian Arctic (> 60∘ N, 60–141∘ W) may undergo drastic changes if the Arctic warming trend continues. For methane (CH4), Arctic reservoirs are large and widespread, and the climate feedbacks from such changes may be potentially substantial. Current bottom-up and top-down estimates of the regional CH4 flux range widely. This study analyzes the recent observations of atmospheric CH4 from five arctic monitoring sites and presents estimates of the regional CH4 fluxes for 2012–2015. The observational data reveal sizeable synoptic summertime enhancements in the atmospheric CH4 that are distinguishable from background variations, which indicate strong regional fluxes (primarily wetland and biomass burning CH4 emissions) around Behchoko and Inuvik in the western Canadian Arctic. Three regional Bayesian inversion modelling systems with two Lagrangian particle dispersion models and three meteorological datasets are applied to estimate fluxes for the Canadian Arctic and show relatively robust results in amplitude and temporal variations across different transport models, prior fluxes, and subregion masking. The estimated mean total CH4 flux for the entire Canadian Arctic is 1.8±0.6 Tg CH4 yr−1. The flux estimate is partitioned into biomass burning of 0.3±0.1 Tg CH4 yr−1 and the remaining natural (wetland) flux of 1.5±0.5 Tg CH4 yr−1. The summer natural CH4 flux estimates clearly show inter-annual variability that is positively correlated with surface temperature anomalies. The results indicate that years with warmer summer conditions result in more wetland CH4 emissions. More data and analysis are required to statistically characterize the dependence of regional CH4 fluxes on the climate in the Arctic. These Arctic measurement sites will aid in quantifying the inter-annual variations and long-term trends in CH4 emissions in the Canadian Arctic.

Effect of simulated acid rain on CO2, CH4 and N2O fluxes and rice productivity in a subtropical Chinese paddy field

The need of more food production, an increase in acidic deposition and the large capacity of paddy to emit greenhouse gases all coincide in several areas of China. Studying the effects of acid rain on the emission of greenhouse gases and the productivity of rice paddies are thus important, because these effects are currently unknown. We conducted a field experiment for two rice croppings (early and late paddies independent experiment) to determine the effects of simulated acid rain (control, normal rain, and treatments with rain at pH of 4.5, 3.5 and 2.5) on the fluxes of CO2, CH4 and N2O and on rice productivity in subtropical China. Total CO2 fluxes at pHs of 4.5, 3.5 and 2.5 were 10.3, 9.7 and 3.2% lower in the early paddy and 28.3, 14.8 and 6.8% lower in the late paddy, respectively, than the control. These differences from the control were significant for pH 3.5 and 4.5. Total CH4 fluxes at pHs of 4.5, 3.5 and 2.5 were 50.4, 32.9 and 25.2% lower in the early paddy, respectively, than the control. pH had no significant effect on CH4 flux in the late paddy or for total (early + late) emissions. N2O flux was significantly higher at pH 2.5 than 3.5 and 4.5 but did not differ significantly from the flux in the control. Global-warming potentials (GWPs) were lower than the control at pH 3.5 and 4.5 but not 2.5, whereas rice yield was not appreciably affected by pH. Acid rain (between 3.5 and 4.5) may thus significantly affect greenhouse gases emissions by altering soil properties such as pH and nutrient pools, whereas highly acidic rain (pH 2.5) could increase GWPs (but not significantly), probably partially due to an increase in the production of plant litter.

Methane production potential and emission at different water levels in the restored reed wetland of Hangzhou Bay.

Changes in the hydrological conditions of coastal wetlands may potentially affect the role of wetlands in the methane (CH4) cycle. In this study, the CH4 production potential and emissions from restored coastal reed wetlands at different water levels were examined in eastern China at a field scale in two phenological seasons. Results showed that the total CH4 flux from reeds at various water levels were positive, indicating that they were “sources” of CH4. During the peak growing season, CH4 flux from reeds was greater than that during the spring thaw. CH4 flux from reeds in inundated conditions was greater than that in non-inundated conditions. The CH4 production potential during the peak growing season was far greater than that during the spring thaw. However, the effect of water level on wetland CH4 production potential differed among seasons. The correlations among CH4 production potential, soil properties and CH4 flux change at different water level. These results demonstrate that water level was related to CH4 production and CH4 flux. The growing season also plays a role in CH4 fluxes. Controlling the hydrological environment in restored wetlands has important implications for the maintenance of their function as carbon sinks.

Minimum tillage of a cover crop lowers net GWP and sequesters soil carbon in a California vineyard

The net global warming potential (GWP) of a cropping system describes net exchanges of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Greenhouse gas intensity (GHGI) relates net GWP to productivity. The use of a barley cover crop was tested in a California vineyard from 2003 to 2010 under two alternative tillage systems, along with a business-as-usual control treatment with incorporation of native weeds. The aim was a comprehensive assessment of barleýs potential to sequester carbon in the soil, and of related (tillage-derived) effects on the vineyard́s net GWP and GHGI. Measurements were made over two years (2009–2010) and included surface fluxes of N2O and CH4, differences in soil carbon, fuel consumption and yield. Above- and belowground net primary productivity (ANPP and BNPP) were also measured to enable further calculations of carbon input. Over 7 years yields and ANPP were lowered under minimum tillage, but soil carbon accumulation in this treatment produced a net GWP of approx. −873kg CO2-eq ha−1 yr−1, which would remain negative over a timeframe of at least 31 years, allowing for removal of vines but not for deep tillage. Conventional-tilled alleys with and without cover crops had positive net GWP because their treatments caused little or no gain in soil carbon and their net GWPs could only be considered negative if wood accumulation was included. Fuel combustion contributed the most to net GWP, followed by soil carbon loss under twice-yearly tillage. Total N2O emissions accounted for 63–76kg CO2–eq ha−1 yr−1. In a vineyard where 8.4–16.8kgNha−1 yr−1 were applied, 90% of N2O emissions occurred at least 4 months after fertigation, mainly following precipitation. Total CH4 fluxes were negative and offset 5–10kg CO2–eq ha−1 yr−1. A minimum-tilled system with cover crops offers potential for important GWP offsets in this climate and soil, if possible negative impacts on yields are acceptable.

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.

Evaluation on the decomposability of tropical forest peat soils after conversion to an oil palm plantation

To understand the variations in the decomposability of tropical peat soil following deforestation for an oil palm plantation, a field incubation experiment was conducted in Sarawak, Malaysia. Peat soils collected from three types of primary forest, namely Mixed Peat Swamp (MPS; Gonystylus-Dactylocladus-Neoscrotechinia association), Alan Batu (ABt; Shorea albida-Gonstylus-Strenonurus association), and Alan Bunga (ABg; Shorea albida association), were packed in polyvinyl chloride pipes and installed in an oil palm plantation. Carbon dioxide (CO2) and methane (CH4) fluxes from soil were monthly measured for 3years. Environmental variables including soil temperature, soil moisture content, and groundwater table were also monitored. The pH, loss on ignition, and total carbon (C) content were similar among the three soils, while total N content was larger in the MPS than in the ABg soils. Based on 13C nuclear magnetic resonance (NMR) spectroscopy, C composition of the MPS and ABg soils was characterized by the largest proportion of C present as alkyl C and O-alkyl C, respectively. The C composition of the ABt soil was intermediate between the MPS and ABg soils. The CO2 fluxes from the three soils ranged from 78 to 625mgCm−2h−1 with a negative correlation to groundwater level. The CH4 fluxes ranged from −67 to 653μgCm−2h−1. Both total CO2 and CH4 fluxes were larger in the order ABg>ABt>MPS (P<0.05). Annual rate of peat decomposition as was estimated from cumulative C loss differed up to 2 times, and the rate constant in exponential decay model was 0.033y−1 for the MPS soil and 0.066y−1 for the ABg soil. The field incubation results of the three forest peat soils seem to reflect the difference in the labile organic matter content, represented by polysaccharides.

Reservoir Water-Level Drawdowns Accelerate and Amplify Methane Emission.

Water-level fluctuations due to reservoir management could substantially affect the timing and magnitude of reservoir methane (CH4) fluxes to the atmosphere. However, effects of such fluctuations on CH4 emissions have received limited attention. Here we examine CH4 emission dynamics in six Pacific Northwest U.S. reservoirs of varying trophic status, morphometry, and management regimes. In these systems, we show that water-level drawdowns can, at least temporarily, greatly increase per-area reservoir CH4 fluxes to the atmosphere, and can account for more than 90% of annual reservoir CH4 flux in a period of just a few weeks. Reservoirs with higher epilimnetic [chlorophyll a] experienced larger increases in CH4 emission in response to drawdown (R2 = 0.84, p < 0.01), suggesting that eutrophication magnifies the effect of drawdown on CH4 emission. We show that drawdowns as small as 0.5 m can stimulate ebullition events. Given that drawdown events of this magnitude are quite common in reservoirs, our results suggest that this process must be considered in sampling strategies designed to characterize total CH4 fluxes from reservoirs. The extent to which (and the mechanisms by which) drawdowns short-circuit connections between methanogenesis and methanotrophy, thereby increasing net CH4 fluxes to the atmosphere, should be a focus of future work.

Characteristics of Methane Flux Across the Water-air Interface in Subtropical Shallow Ponds

Five shallow ponds of Yichang were selected to illustrate the characteristics of methane(CH4) in subtropical eutrophic shallow ponds. CH4 flux across the water-air interface was quantified with static floating chamber method for one year. Annual CH4 fluxes of the five ponds were 4.495, 12.702, 6.827, 8.920, 17.560 mg·(m2·h)-1 respectively. Diffusive CH4 fluxes were 0.075, 0.087, 0.118, 0.086, 0.151 mg·(m2·h)-1 respectively and bubble emissions were 4.420, 12.616, 6.709, 8.834, 17.409 mg·(m2·h)-1 respectively. Over 98% of total CH4 flux was bubble emission and CH4 flux was apparently higher than other aquatic ecosystems. So the CH4 flux of shallow waters was high and bubble emission was the dominant way. CH4 emission would be largely underestimated if the research only focus on the diffusion discharge and ignore the bubble emission.

Spatial and temporal variability of CO2and CH4gas transfer velocities and quantification of the CH4microbubble flux in mangrove dominated estuaries

AbstractGas transfer velocities (k) of CO2and CH4were determined from 209 deployments of a newly designed floating chamber in six mangrove dominated estuaries in Australia and the United States to estimate mangrove system specifick.k600‐CO2andk600‐CH4(knormalized to the Schmidt number of 600) varied greatly within and between mangrove creeks, ranging from 0.9 cm h−1to 28.3 cm h−1. The gas transfer velocity correlated well with current velocity at all study sites suggesting current generated turbulence was the main driver controllingk. An empirical relationship that accounts for current velocity and a linearly additive contribution of wind speed and water depth was a good predictor ofk600‐CO2(R2 = 0.67) andk600‐CH4(R2 = 0.57) in the mangrove creeks in Australia. In a side‐by‐side study, good agreement was found betweenkdetermined from this new floating chamber and a3He/SF6dual tracer release experiment (∼5% discrepancy).k600‐CH4correlated well withk600‐CO2(R2 = 0.81), however,k600‐CH4was on average 1.2 times higher thank600‐CO2, most likely reflecting a microbubble flux contribution. The microbubble flux contributed up to 73% of the total CH4flux and was best predicted by a model that included CH4supersaturation, temperature, and current velocity. A large overestimation was found for both CO2and CH4fluxes when calculated using empirically derivedkmodels from previous studies in estuaries. The high temporal and spatial variabilities ofkCO2andkCH4highlights the importance of site specific transfer velocity measurements in dynamic ecosystems such as mangrove estuaries.

A multi-year estimate of methane fluxes in Alaska from CARVE atmospheric observations.

Methane (CH4) fluxes from Alaska and other arctic regions may be sensitive to thawing permafrost and future climate change, but estimates of both current and future fluxes from the region are uncertain. This study estimates CH4 fluxes across Alaska for 2012-2014 using aircraft observations from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) and a geostatistical inverse model (GIM). We find that a simple flux model based on a daily soil temperature map and a static map of wetland extent reproduces the atmospheric CH4 observations at the state-wide, multi-year scale more effectively than global-scale, state-of-the-art process-based models. This result points to a simple and effective way of representing CH4 flux patterns across Alaska. It further suggests that contemporary process-based models can improve their representation of key processes that control fluxes at regional scales, and that more complex processes included in these models cannot be evaluated given the information content of available atmospheric CH4 observations. In addition, we find that CH4 emissions from the North Slope of Alaska account for 24% of the total statewide flux of 1.74 ± 0.44 Tg CH4 (for May-Oct.). Contemporary global-scale process models only attribute an average of 3% of the total flux to this region. This mismatch occurs for two reasons: process models likely underestimate wetland area in regions without visible surface water, and these models prematurely shut down CH4 fluxes at soil temperatures near 0°C. As a consequence, wetlands covered by vegetation and wetlands with persistently cold soils could be larger contributors to natural CH4 fluxes than in process estimates. Lastly, we find that the seasonality of CH4 fluxes varied during 2012-2014, but that total emissions did not differ significantly among years, despite substantial differences in soil temperature and precipitation; year-to-year variability in these environmental conditions did not affect obvious changes in total CH4 fluxes from the state.

Rising plant-mediated methane emissions from arctic wetlands.

Plant-mediated CH4 flux is an important pathway for land-atmosphere CH4 emissions, but the magnitude, timing, and environmental controls, spanning scales of space and time, remain poorly understood in arctic tundra wetlands, particularly under the long-term effects of climate change. CH4 fluxes were measured insitu during peak growing season for the dominant aquatic emergent plants in the Alaskan arctic coastal plain, Carex aquatilis and Arctophila fulva, to assess the magnitude and species-specific controls on CH4 flux. Plant biomass was a strong predictor of A.fulva CH4 flux while water depth and thaw depth were copredictors for C.aquatilis CH4 flux. We used plant and environmental data from 1971 to 1972 from the historic International Biological Program (IBP) research site near Barrow, Alaska, which we resampled in 2010-2013, to quantify changes in plant biomass and thaw depth, and used these to estimate species-specific decadal-scale changes in CH4 fluxes. A ~60% increase in CH4 flux was estimated from the observed plant biomass and thaw depth increases in tundra ponds over the past 40years. Despite covering only ~5% of the landscape, we estimate that aquatic C.aquatilis and A.fulva account for two-thirds of the total regional CH4 flux of the Barrow Peninsula. The regionally observed increases in plant biomass and active layer thickening over the past 40years not only have major implications for energy and water balance, but also have significantly altered land-atmosphere CH4 emissions for this region, potentially acting as a positive feedback to climate warming.

Greenhouse gas fluxes from a grazed grassland soil after slurry injections and mineral fertilizer applications under the Atlantic climatic conditions of NW Spain

The number of studies that investigate how agricultural practices on dairy farms in the North West (NW) of Spain affect greenhouse gas (GHG) fluxes from soils is limited. Thus, the objective of this study was to quantify the effects of the application of mineral fertilizers and cattle slurry injections on GHG fluxes from a grassland soil with grazing dairy cattle, in Galicia (NW Spain). We also aimed to identify the type of fertilizer associated with high grass production and low GHG fluxes. To achieve this, fluxes of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2), grass yields and soil mineral nitrogen (N) contents were monitored after three applications (in spring, summer and autumn) of surface broadcasted mineral fertilizer (MN) and injected cattle slurry (CS) and compared with no fertilization (zero N). Dry soil conditions (<60% water-filled pore space (WFPS)) were observed during the spring and summer, contrasting with the higher soil WFPS (>60%) in autumn due to the more frequent rainfall. Overall, total cumulative N2O fluxes from CS were similar than from MN (P>0.05), indicating that denitrification in this C-rich soil was not stimulated by slurry-carbon applications. Large losses of CH4 and CO2 were related to CS, but overall only total cumulative CH4 fluxes were larger with respect to MN (P<0.05). Dry weather conditions would have stimulated organic matter mineralization in this soil, which resulted in the low efficiency of both fertilizers to increase yields. As we obtained similar total CO2 equivalents to produce same yields with both types of fertilization (P>0.05), this study did not show a clear type of fertilization related to low GHG fluxes and high yields. We believe that longer-term studies are required to provide more robust estimations and conclusions about the effect of fertilizer applications on GHG fluxes from grassland soils in NW Spain.

Divergent drivers of carbon dioxide and methane dynamics in an agricultural coastal floodplain: Post-flood hydrological and biological drivers

Many coastal floodplains have been artificially drained for agriculture, altering hydrological connectivity and the delivery of groundwater-derived solutes including carbon dioxide (CO2) and methane (CH4) to surface waters. Here, we investigated the drivers of CO2 and CH4 within the artificial drains of a coastal floodplain under sugarcane plantation and quantify the contribution of groundwater discharge to CO2 and CH4 dynamics over a flood event (290mm of rainfall). High temporal resolution, in situ observations of dissolved CO2 and CH4, carbon stable isotopes of CH4 (δ13C-CH4), and the natural groundwater tracer radon (222Rn) allowed us to quantify CO2, CH4 and groundwater dynamics during the rapid recession of a flood over a five day period. Extreme super-saturation of free CO2 ([CO2*]) up to 2,951μM (25,480% of atmospheric equilibrium) was driven by large groundwater input into the drains (maximum 87cmday−1), caused by a steep hydraulic head in the adjacent water table. Groundwater input sustained between 95 and 124% of the surface [CO2*] flux during the flood recession by delivering high carbonate alkalinity groundwater (DIC=10,533μM, ~pH=7.05) to acidic surface water (pH <4), consequently transforming all groundwater-derived DIC to [CO2*]. In contrast, groundwater was not a major direct driver of CH4 contributing only 14% of total CH4 fluxes. A progressive increase in CH4 concentrations of up to ~2400nMday−1 occurred as a combination of increased substrate availability delivered by post-flood drainage water and longer residence times, which allowed for a biogenic CH4 signal to develop. The progressive enrichment in δ13C-CH4 values (−70‰ to −48‰) and increase in CH4 concentrations (46–2460nM) support coupled production-oxidation, with concentrations and δ13C values remaining higher (2,798nM and -47‰) than pre-flood conditions (534nM and -55‰) three weeks after the flood. Our findings demonstrate how separate processes can drive the aquatic CO2 and CH4 response to a flood event in a drained coastal floodplain, and the key role groundwater had in post-flood [CO2*] evasion to the atmosphere, but not CH4.

Different responses of nitrogen fertilization on methane emission in rice plant included and excluded soils during cropping season

Since nitrogen (N) fertilization is the most efficient practice for increasing rice production, N fertilizer consumptions have continued to increase globally. Therefore, the effects of N fertilization on CH4 emission characteristics have been extensively studied. However, no consistent conclusions to N fertilization on CH4 cycles have been drawn so far. In order to evaluate the effect of N fertilization on CH4 fluxes in rice fields, N fertilizer (urea) was applied at different levels (0–180kgNha−1) in a typical temperate paddy soil, and CH4 emissions were characterized under two different soil conditions during cropping seasons (rice plant included and excluded soils). Seasonal CH4 fluxes responded differently to N fertilization between the rice plants included and excluded soils. In rice plant excluded soils, total CH4 fluxes significantly increased with increasing N fertilization levels. However, in rice plant included soils, seasonal CH4 fluxes changed with a quadratic response. Total CH4 fluxes increased with increasing N fertilization by 115–137kgNha−1 and later decreased. The difference in seasonal CH4 fluxes between the two soils might be caused by rice rhizospheric activities and this difference could be defined as the minimum CH4 oxidation potentials of rice rhizosphere. This CH4 oxidation potential significantly increased with increasing N fertilization levels, and is highly correlated with total biomass, straw and root biomass productivities. Therefore, the decrease in CH4 fluxes by high levels of N fertilization in rice plant included soils might be caused by the increasing N fertilization-induced CH4 consumption.

Effect of barley straw biochar application on greenhouse gas emissions from upland soil for Chinese cabbage cultivation in short-term laboratory experiments

Chinese cabbage was cultivated in upland soil with the addition of biochar in order to investigate the potential for reduction of greenhouse gas emissions. Barley straw biochar (BSB) was introduced in a Wagner pot (1/5000a) in amounts of 0 (BSB0, control), 100 (BSB100), 300 (BSB300), and 500 (BSB500) kg 10a-1. After the addition of BSB into the upland soil, carbon dioxide (CO2) emission increased while methane (CH4) and nitrous oxide (N2O) emissions decreased. The highest CO2 flux was measured for the BSB500 sample, (84.6 g m-2) followed by BSB300, BSB100, and BSB0 in decreasing order. Relative to those of control, the total CH4 flux and N2O flux for the BSB500 treatment were lower by 31.6% and 26.1%, respectively. The global warming potential (GWP) of the treatment without biochar was 281.4 g CO2 m-2 and those for treatments with biochar were in the range from 194.1 to 224.9 g CO2 m-2. Therefore, introducing BSB into upland soil to cultivate Chinese cabbages can reduce the global warming potential.

High-Resolution Classification of South Patagonian Peat Bog Microforms Reveals Potential Gaps in Up-Scaled CH4 Fluxes by use of Unmanned Aerial System (UAS) and CIR Imagery

South Patagonian peat bogs are little studied sources of methane (CH4). Since CH4 fluxes can vary greatly on a small scale of meters, high-quality maps are needed to accurately quantify CH4 fluxes from bogs. We used high-resolution color infrared (CIR) images captured by an Unmanned Aerial System (UAS) to investigate potential uncertainties in total ecosystem CH4 fluxes introduced by the classification of the surface area. An object-based approach was used to classify vegetation both on species and microform level. We achieved an overall Kappa Index of Agreement (KIA) of 0.90 for the species- and 0.83 for the microform-level classification, respectively. CH4 fluxes were determined by closed chamber measurements on four predominant microforms of the studied bog. Both classification approaches were employed to up-scale CH4 closed chamber measurements in a total area of around 1.8 hectares. Including proportions of the surface area where no chamber measurements were conducted, we estimated a potential uncertainty in ecosystem CH4 fluxes introduced by the classification of the surface area. This potential uncertainty ranged from 14.2 mg·m−2·day−1 to 26.8 mg·m−2·day−1. Our results show that a simple classification with only few classes potentially leads to pronounced bias in total ecosystem CH4 fluxes when plot-scale fluxes are up-scaled.

Unexpected stimulation of CH4 emissions under continuous no-tillage system in mono-rice paddy soils during cultivation

No-tillage (NT) is known as an effective method of soil management that has the potential to increase soil organic carbon (SOC) accumulation in arable lands. Unlike upland soils, the increase of SOC accumulation in paddy soils under continuous NT is likely to increase methane (CH4) emissions during rice cultivation. However, the interaction between the SOC accumulation and CH4 emission characteristics associated with continuous NT in rice paddies has not been well elucidated. To investigate the effects of continuous NT on SOC accumulation and CH4 emissions, conventional tillage (CT) and NT plots were installed in a typical mono-rice paddy soil classified as a fine-silty, mixed, nonacid mesic Typic endoaquept in the southern part of the Korean peninsula in 2007. In the 1st, 2nd and 5th years after installation, the CH4 emission patterns were characterised during rice cultivation and rice grain yield and soil properties were investigated at the harvesting stage. Compared with CT (381 – 363 kg CH4 ha-1), NT effectively decreased total CH4 fluxes by approx. 20-27% in the 1st and 2nd years (279 – 291 kg CH4 ha-1) after installation. However, a much higher CH4 flux (approx. 36%) was observed in the NT (385 kg CH4 ha-1) than the CT (287 kg CH4 ha-1) plots in the 5th year. The SOC content in the NT plots clearly increased over the study years (14.5 – 15.6 g kg-1) compared with that under CT (14.4 - 14.3 g kg-1) which did not change significantly during the study period. Similar to the increase of the SOC content observed under NT, the concentrations of labile C forms such as water-extractable C (WEC) and hot water-extractable C (HWEC) and labile C availability in the surface soil dramatically increased over the study years, which may have increased mcrA gene copies as a methanogen population abundance (5.7 × 106mcrA gene copy number g-1 soil) and CH4 production potentials in the 5th year compared with CT (4.2 × 106mcrA gene copy number g-1 soil). Rice productivity was slightly lower in the NT than the CT treatment, though this difference was not statistically significant across the study years. These findings led to the conclusion that because continuous NT can increase CH4 emissions during rice cultivation under flooded paddy soil conditions due to the increased availability of labile forms of SOC, therefore, other soil management regimes that can decrease CH4 emissions, such an intermittent drainage, should be introduced along with continuous no-tillage.

Regulation of methane production, oxidation, and emission by vascular plants and bryophytes in ponds of the northeast Siberian polygonal tundra

AbstractMethane (CH4) production, oxidation, and emission were studied in ponds of the permafrost‐affected polygonal tundra in northeast Siberia. Microbial degradation of organic matter in water‐saturated soils is the most important source for the climate‐relevant trace gas CH4. Although ponds and lakes cover a substantial fraction of the land surface of northern Siberia, data on CH4 fluxes from these water bodies are scarce. Summer CH4 fluxes were measured with closed chambers at the margins of ponds vegetated by vascular plants and in their centers without vascular plants. Furthermore, CH4 and oxygen concentration gradients, stable carbon isotope signatures of dissolved and emitted CH4, and microbial CH4 production and CH4 oxidation were determined. Mean summer fluxes were significantly higher at the margins of the ponds (46.1 ± 15.4 mg CH4 m−2 d−1) than at the centers (5.9 ± 8.2 mg CH4 m−2 d−1). CH4 transport was dominated by diffusion in most open water sites, but substantial ebullitive fluxes (12.0 ± 8.1 mg CH4 m−2 d−1) were detected in one pond. Plant‐mediated transport accounted for 70 to 90% of total CH4 fluxes above emerged vegetation. In the absence of vascular plants, 61 to 99% of the CH4 produced in the anoxic bottom soil was consumed in a layer of the submerged moss Scorpidium scorpioides, which covered the bottoms of the ponds. The fraction of CH4 oxidized was lower at sites with vascular plants since CH4 was predominantly transported through their aerenchyma, thereby bypassing the CH4 oxidation zone in the moss layer. These results emphasize the importance of moss‐associated CH4 oxidation causing low CH4 fluxes from the studied Siberian ponds.

Biosphere–atmosphere exchange of methane in India as influenced by multiple environmental changes during 1901–2010

It is highly uncertain on how human and natural environmental factors have altered methane (CH4) emissions from terrestrial ecosystems in India. Using a process-based, Dynamic Land Ecosystem Model (DLEM) driven by climate, land cover and land use change (LCLUC), atmospheric nitrogen deposition (NDEP), atmospheric carbon dioxide (CO2) concentration, and tropospheric ozone (O3) pollution, we examined CH4 flux from terrestrial in India during 1901–2010. The DLEM simulations have shown that total CH4 flux over the country ranged from 2.9 Tg C year−1 to 6.5 Tg C year−1 with significant inter-annual variations driven by climate during 1901–2010. Contemporary CH4 emissions have primarily occurred from rice fields (3.9 ± 0.9 Tg C year−1) while wetlands contributed to 2.1 ± 0.6 Tg C year−1 in the 2000s. During 1901–2010, total CH4 emission from the terrestrial biosphere has increased by ∼2.1 Tg C year−1. LCLUC has increased CH4 emissions by 2.3 Tg C year−1 primarily due to increase in the rice-based cropping systems as well as irrigation expansion during the study period. Elevated CO2 concentration stimulated plant biomass production in both rice fields and wetlands that increased CH4 emissions by 0.7 Tg C year−1. On the contrary, climate change decreased net CH4 emissions by ∼1.2 Tg C year−1 due to negative effects of extreme high temperature as well as occurrences of extreme drought events on plant growth. Our study suggests that LCLUC and elevated CO2 concentration have significantly increased CH4 emissions from terrestrial ecosystems in India.