Submerged macrophytes enhance carbon emission (CO2 and CH4) from the freshwater wetland in Keibul Lamjao National Park, Manipur, India

Accurate estimation of methane (CH4) and carbon dioxide (CO2) emissions requires precise sampling methods due to the significant variability of these gases. This study, part of the project breed4green in Austria, investigated the variability of CH4 and CO2 and minimum number of spot samples required to accurately estimate CH4 and CO2 emissions from dairy cows on commercial farms. A total of 51,895 spot samples from 451 cows on 9 farms were analyzed, which were obtained using the GreenFeed system. Each farm participated in 2 GreenFeed measurement periods (Period 1 and 2), each lasting 6 wk and separated by 3 to 6 mo. A total of 298 cows, each with at least 70 spot samples in either Period 1 or Period 2, were analyzed to determine the minimum number of spot samples. Two methods were used. In the first, forward sampling, subsets of increasing spot samples (the first 1, 10, 20, 30, 40, 50, 60 and 70 measurements per cow) were compared with the complete set of available measurements for the cows. In the second method, random sampling, the same number of spot samples were selected randomly from all available visits for each cow and this procedure was repeated 100 times to account for sampling variability. The minimum number of spot samples required was determined when the Pearson correlation between the arithmetic mean of the subset and that of all available measurements reached a value of 0.90. Mean CH4 and CO2 emissions were 430 g/d and 13,309 g/d, respectively. The coefficient of variation (CV) for diurnal variability ranged from 4.6 to 12.0% for CH4 and from 2.7 to 6.9% for CO2, indicating low to moderate diurnal variability. Day-to-day variability was low, with CV between 3.7 and 8.7% for CH4 and between 2.5 and 8.7% for CO2. Substantial within-cow variation was observed for CH4 (mean CV of 22.5%), while CO2 was more stable (mean CV of 11.7%). When using forward sampling, at least 19 spot samples were required for accurate CH4 estimates and only 13 for CO2, with a mean of 6.5 and 4.3 d needed to obtain these measurements, respectively. When using random sampling, only 8 spot samples for CH4 and 5 spot samples for CO2 were sufficient to meet the accuracy criteria. For future analyses of this data set, we will rely on the results of forward sampling. Forward sampling is based on the actual sequence of visits made by each cow to the GreenFeed and therefore offers a more conservative and realistic approach compared with random sampling. Overall, the results highlight the dynamic nature of CH4 emissions, which are influenced by factors such as feeding patterns and rumen fluctuations and suggest that more spot samples are needed for reliable estimates of CH4 than for CO2.

Emission of carbon dioxide (CO2) and methane (CH4) is of interest in tropical wetland studies because the high and relatively stable temperatures year-round enhance both primary productivity and organic matter decomposition. Nonetheless, there is scarcity of data on emission of these carbon-based greenhouse gases from tropical wetlands. We investigated CO2 and CH4 fluxes from a natural tropical freshwater wetland in Uganda under different dominant vegetation communities, i.e., Cyperus papyrus (Papyrus), Typha latifolia (Typha) and Phragmites mauritianus (Phragmites), during the dry and wet seasons. Gas samples were collected using static chambers and analyzed by gas chromatography. Fluxes (mg C m−2 h−1) of both CO2 and CH4 from Papyrus (732.9 ± 48.7 [mean ± standard error] and 14.1 ± 0.8, respectively) and from Typha (759.7 ± 51.4 and 13.5 ± 1.2, respectively) insignificantly varied (p > 0.05) during the dry season. However, CO2 and CH4 fluxes from both vegetation communities during this season were significantly lower and higher (p 0.05) occurred among the three vegetation communities for both CO2 and CH4 fluxes (Phragmites: 691.9 ± 55.8 and 15.6 ± 1.1, Typha: 682.0 ± 53.3 and 16.3 ± 1.2, and Papyrus: 651.2 ± 49.0 and 17.1 ± 1.7, respectively). Water level was the main driver of CO2 and CH4 fluxes from the wetland, suggesting its importance in any efforts to regulate fluxes of both gases in tropical wetlands. We estimated total annual CO2 and CH4 emissions from Uganda’s wetland soils in the ranges of 159.5 × 106–180.2 × 106 t C (tonnes of carbon) and 278.9 × 104–359.7 × 104 t C, respectively. • Vegetation community does not influence CO2 and CH4 fluxes from a tropical freshwater wetland soil under continuous flooding • High water level in a tropical freshwater wetland lowers CO2 flux but increases CH4 flux • A wetland’s role in climate change mitigation is a function of carbon sequestration and emission

Climatic temperature controls the geographical patterns of coastal marshes greenhouse gases emissions over China

Methane emissions along biomethane and biogas supply chains are underestimated

In recent years， the rapid socio-economic development and the improvement of people's diets have driven the conversion of paddy soil to upland crop cultivation， leading to changes in soil water content， carbon and nitrogen availability， and the intensity of greenhouse gas emission. Therefore， it is crucial to study the effects of changes in soil water content and carbon and nitrogen availability on greenhouse gas CH4 and CO2 emissions and identify the key controlling factors upon rice paddy conversion into upland field， especially during the initial stage of conversion. Soil samples used in the present study were collected from a long-term rice paddy field and an adjacent upland field previously converted from rice paddy. The paddy soil was set into submerged （water to soil ratio of 2∶1） and from submerged to a slowly draining treatment （water to soil ratio of 2∶1 slowly decreased to 70% field water capacity and then remained stable） and compared with the upland soil （soil water content remained at 70% field water capacity）. Under each water gradient， the soil was supplied with labile C and N to change substrate availability： ① control （no substrate addition）， ② C addition （glucose）， ③ N addition （NH4Cl）， and ④ C and N additions （glucose+NH4Cl）. CH4 and CO2 emissions and soil biochemical properties were measured regularly during the incubation period so as to investigate the effects of soil water content， carbon and nitrogen availability， and their interaction on CH4 and CO2 emissions in paddy soil. The changes in contents of soil microbial biomass carbon （ΔMBC）， dissolved organic carbon （ΔDOC）， and soil mineral N （ΔMineral-N， containing ΔNH4+-N and ΔNO3--N） over the incubation period were calculated by subtracting the initial values from the final values at the end of the incubation period. The results showed that as compared to the submerged condition， the drainage of submerged paddy soil significantly reduced CH4 emission by 95% on average and increased CO2 emission by 46% on average. The cumulative emissions of CH4 and CO2 were significantly higher in drained paddy soil （1.36 mg·kg-1 and 584.13 mg·kg-1 for CH4 and CO2， respectively） relative to those in upland soil （0.01 mg·kg-1 and 407.70 mg·kg-1）. CH4 emissions from the submerged paddy soil significantly increased by 40% after carbon addition and decreased by 63% after nitrogen addition. The simultaneous additions of carbon and nitrogen had little effect on the CH4 emissions from submerged paddy soil. CH4 emissions from the drained paddy soil increased significantly by 48% after carbon addition， but there was no significant difference among other substrate addition treatments. In upland soil， the additions of carbon and nitrogen had no significant effect on CH4 emissions but significantly increased CO2 emissions by 45%-109%. The additions of carbon and nitrogen had little effect on CO2 emissions in submerged paddy soil. The concurrent addition of carbon and nitrogen significantly increased CO2 emissions by 36% in drained paddy soil. The interactions between soil water change and N addition had no significant effect on CH4 emissions， while the interactions between soil water change and C and CN additions significantly affected CH4 emissions. No significant interactions between soil water change and C and N availability were observed for CO2 emissions. The conversion of submerged paddy to upland soil decreased soil pH， DOC， MBC， and NH4+-N contents but increased NO3--N content. The additions of carbon and nitrogen significantly affected soil biochemical properties. The results of correlation analysis showed that CH4 emissions were significantly positively correlated with soil pH， ΔMBC， and ΔNH4+-N and negatively correlated with ΔNO3--N among treatments. Conversely， CO2 emissions were significantly positively correlated with ΔNO3--N but negatively correlated with pH， ΔDOC， ΔMBC， and ΔNH4+-N. The changes of soil chemical and biological properties induced by soil water change and carbon and nitrogen availability were the main factors influencing CH4 and CO2 emissions from paddy soil. In summary， changes in soil water content and carbon and nitrogen availability affect CH4 and CO2 emissions by altering soil biochemical properties. Drainage of paddy soil is an effective measure to reduce CH4 emissions， but the risk of increased CO2 emissions during the short-term period upon drainage should be considered. Therefore， when developing strategies for rice paddy management， it is crucial to consider the combined effects of water and C and N management so as to achieve effective greenhouse gas mitigation and green and sustainable agricultural production.

Although lakes are important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere contributing to global warming, their CH4 and CO2 emissions are rarely assessed. In particular, increasing inputs of terrestrial dissolved organic carbon (DOC) may affect gas dynamics and alter seasonal changes in gas production. Here, we analysed variations in CH4 and CO2 dynamics in sub‐basins of an acidic bog lake, which was artificially divided into four quarters three decades ago, leading to divergence in water chemistry and biology. In the divided lake, only the south‐west basin (SW) received DOC inputs from an adjacent peat bog, while the north‐east basin (NE) was hydrologically disconnected. A year‐long determination of CH4 and CO2 production and emission patterns in the two contrasting basins exposed the indirect mechanisms by which DOC supply exercised control on greenhouse gas dynamics in this shallow lake. In both basins, dissolved CH4 was negatively correlated with dissolved oxygen (O2) through the water column, suggesting that aerobic methanotrophy is an important regulator of CH4 emissions in this lake. In contrast, the amount of CO2 stored in oxic and anoxic layers was not significantly different between the basins, suggesting that O2 is not the most important driver of dissolved CO2. Estimated total CH4 and CO2 emissions were 2.1 and 1.7 times lower in the NE basin than in the SW basin, with major CH4 and CO2 emissions occurring during the fall turnover. The differences in CH4 and CO2 emissions suggest that the hydro‐physical properties, namely seasonal temperature, the duration of stratification and O2 availability, are the main drivers of CH4 and CO2 emissions to the atmosphere from small shallow lakes under the influence of DOC inputs under global warming pressure.

Flooding lowers the emissions of CO2 and CH4 during the freeze-thaw process in a lacustrine wetland

Methane and carbon dioxide emissions from manure storage facilities at two free-stall dairies

River ecosystems have emerged as important sources of greenhouse gases (GHGs), yet the dynamics of greenhouse gas (GHG) fluxes at the water-air interface (WAI) in dammed rivers affected by algal blooms (ABs) remain poorly understood. In particular, the influence of different algal bloom (AB) phases on carbon dioxide (CO2) and methane (CH4) emissions is not well characterized. Here we investigate spatiotemporal variations in CO2 and CH4 concentrations and fluxes in a subtropical dammed river reservoir in China during both the growth and decay phases of ABs. We found that the dominant algal taxa included Cyanobacteria, Bacillariophyta, and Chlorophyta, with cyanobacterial blooms prevailing throughout the period. Overall, the mean CO₂ and CH₄ concentrations across the whole reservoir were 163.12 ± 18.77 and 19.51 ± 3.59 μmol/L (mean ± SD), with corresponding fluxes of 9.44 ± 1.32 mmol/m²/h and 32.52 ± 27.45 μmol/m²/h, respectively. Notably, both gases exhibited consistently higher concentrations in the bottom waters than in the surface. Fluxes of both CO₂ (p < 0.01) and CH₄ (p < 0.05) were remarkably elevated during the non-AB phase relative to the AB phase. Chlorophyll-a (Chl-a), water temperature (Tw), and dissolved total nitrogen (DTN) may be the important factors influencing the pattern of CO2 concentration changes. DTN and dissolved organic carbon (DOC) were identified as key factors regulating CO₂ flux variations. They explained 91% and 80% of the variation in CO2 concentration and flux, respectively. During the AB phase, key environmental factors including pH, Chl-a, algal density (AD) and Tw exhibited significantly higher values (p < 0.01) compared to the non-AB phase. We propose that thermal stratification, shaped by seasonal warming and AB dynamics, plays a critical role in modulating GHG production and transport. These findings highlight how environmental transitions during distinct AB phases govern carbon cycling in dammed river ecosystems, and provide critical insights into the dynamic mechanisms of GHG flux under shifting AB regimes. Highlights During the growth phase of the algal bloom, CO₂ emissions from the reservoir decrease significantly. During the decline phase of the algal bloom, both CO₂ and CH₄ fluxes increase significantly at the water-air interface of the reservoir. Different phases of the algal bloom drive changes in environmental factors that affect the concentrations of CO2 and CH4. The concentrations of CO2 and CH₄ are higher in the bottom waters than in the surface. Values of emission factors estimated by the IPCC are lower than those observed in the field.

Abstract. Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH4) and carbon dioxide (CO2) emissions from northern lakes. Here we assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska to lakes' physicochemical properties and geographic characteristics, including permafrost soil type surrounding lakes. Emission modes included direct ebullition, diffusion, storage flux, and a newly identified ice-bubble storage (IBS) flux. We found that all lakes were net sources of atmospheric CH4 and CO2, but the climate warming impact of lake CH4 emissions was 2 times higher than that of CO2. Ebullition and diffusion were the dominant modes of CH4 and CO2 emissions, respectively. IBS, ~10% of total annual CH4 emissions, is the release to the atmosphere of seasonally ice-trapped bubbles when lake ice confining bubbles begins to melt in spring. IBS, which has not been explicitly accounted for in regional studies, increased the estimate of springtime emissions from our study lakes by 320%. Geographically, CH4 emissions from stratified, mixotrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes throughout the rest of Alaska. The relationship between CO2 emissions and geographic parameters was weak, suggesting high variability among sources and sinks that regulate CO2 emissions (e.g., catchment waters, pH equilibrium). Total CH4 emission was correlated with concentrations of soluble reactive phosphorus and total nitrogen in lake water, Secchi depth, and lake area, with yedoma lakes having higher nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.

Freshwater wetlands are significant carbon sinks, however, altering a wetland’s hydrology can reduce its ability to sequester carbon and may lead to the release of previously stored soil carbon. Rehabilitating a wetland’s water table has the potential to restore the natural process of wetland soil carbon sequestration and storage. Further, little is known about the role of microbial communities that mediate carbon cycling during wetland rehabilitation practices. Here, we examined the carbon emissions and microbial community diversity during a wetland rehabilitation process known as ‘environmental watering’ (rewetting) in an Australian, semi-arid freshwater floodplain wetland. By monitoring carbon dioxide (CO2) and methane (CH4) emissions during dry and wet phases of an environmental watering event, we determined that adding water to a degraded semi-arid floodplain wetland reduces carbon emissions by 28-84%. The watering event increased anoxic levels and plant growth in the aquatic zone of the wetland, which may correlate with lower carbon emissions during and after environmental watering due to lower anaerobic microbial decomposition processes and higher CO2 sequestration by vegetation. During the watering event, areas with higher inundation had lower CO2 emissions (5.15 ± 2.50 g CO2 m-2 d-1) compared to fringe areas surrounding the wetland (11.89 ± 4.25 g CO2 m-2 d-1). CH4 flux was inversely correlated with CO2 emissions during inundation periods, showing a 38% (0.013 ± 0.061 g CO2-e m-2 d-1) increase when water was present in the wetland. During the dry phases of environmental watering, there was CH4 uptake within the fringe and aquatic zones (-0.013 ± 0.063 g CO2-e m-2 d-1). A clear succession of soil microbial community was observed during the dry-wet phases of the environmental watering process. This suggests that wetland hydrology plays a large role in the microbial community structure of these wetland ecosystems, and is consequently linked to CO2 and CH4 emissions. Overall, the total carbon emissions (CO2 + CH4) were reduced within the wetland during and after the environmental watering event, due to increasing vegetative growth and subsequent CO2 sequestration. We recommend environmental watering practices in this degraded arid wetland ecosystem to improve conditions for wetland carbon sequestration and storage.

Climate and soil nutrients control the geographical variations in anaerobic CH4 and CO2 emissions from coastal salt marshes.

At present scenario, estimation of Greenhouse Gas (GHG) emission in the ambient air has becomes a major concern. Emission of GHG has the direct linkage with ambient air pollution and also poses global environmental threats and challenges. Though several scientists are working to mitigate the emission of GHGs but till date no mitigation/management plan has been implemented in global scale. The emission of GHGs are in general from multiple sectors like energy, industry, waste management plant, agricultural sector etc. The major GHGs are methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O). In the present study GHG (CH4, CO2 and N2O) fluxes have been reviewed from wastewater treatment plant (WWTP), constructed wetlands (CWs) and irrigated rice fields (IRF) in India and compared with other countries like Australia, Europe and China. The emission of CH4, CO2 and N2O fluxes from WWTP in Australian condition varied in an average from 0 to 111, 0 to 769 and 0 to 3 ton/year respectively whereas in Indian condition CH4 and N2O fluxes varied in an average from 0 to 6, and 0 to 0.01 ton/year. The higher emission of CH4 and N2O in Australia might be due to higher capacity of WWTP and advance biological treatment plant as compared to India. In Indian and China climatic condition the emission of CH4, CO2 and N2O fluxes from IRF varied from 107 × 104 to 110 × 104, 2116 × 104 to 6096 × 104 and 4 × 104 to 5 × 104, 644 × 104 to 1202 × 104, 205 × 104 to 1208 × 104 and 29 × 104 to 41 × 104 ton/year respectively. The higher fluxes of GHG w.r.t CH4 and N2O might be due to continuous flooding in China, application of nitrogen fertilizers in large scale in the rice field, and likely to be due to overburden pressure for production of rice as compared to India. CWs are the well-known natural CH4 producer in the atmosphere. The emission of CH4 from CWs in India and Europe varied from 46 to 1103 and negative to 38,000 mg/m2/day respectively. CH4 emission depends on tropical coastal wetland condition and type of surface flow in the wetland. India is fewer producers to GHGs as compared to other countries. Appropriate management plan will further reduce the emission of GHGs as well as ambient air pollution.

The objectives of this study were to evaluate the relationship between residual feed intake (RFI; g/d) and enteric methane (CH) production (g/kg DM) and to compare CH and carbon dioxide (CO) emissions measured using respiration chambers (RC) and the GreenFeed emission monitoring (GEM) system (C-Lock Inc., Rapid City, SD). A total of 98 crossbred replacement heifers were group housed in 2 pens and fed barley silage ad libitum and their individual feed intakes were recorded by 16 automated feeding bunks (GrowSafe, Airdrie, AB, Canada) for a period of 72 d to determine their phenotypic RFI. Heifers were ranked on the basis of phenotypic RFI, and 16 heifers (8 with low RFI and 8 with high RFI) were randomly selected for enteric CH and CO emissions measurement. Enteric CH and CO emissions of individual animals were measured over two 25-d periods using RC (2 d/period) and GEM systems (all days when not in chambers). During gas measurements metabolic BW tended to be greater ( ≤ 0.09) for high-RFI heifers but ADG tended ( = 0.09) to be greater for low-RFI heifers. As expected, high-RFI heifers consumed 6.9% more feed ( = 0.03) compared to their more efficient counterparts (7.1 vs. 6.6 kg DM/d). Average CH emissions were 202 and 222 g/d ( = 0.02) with the GEM system and 156 and 164 g/d ( = 0.40) with RC for the low- and high-RFI heifers, respectively. When adjusted for feed intake, CH yield (g/kg DMI) was similar for high- and low-RFI heifers (GEM: 27.7 and 28.5, = 0.25; RC: 26.5 and 26.5, = 0.99). However, CH yield differed between the 2 measurement techniques only for the high-RFI group ( = 0.01). Estimates of CO yield (g/kg DMI) also differed between the 2 techniques ( ≤ 0.03). Our study found that high- and low-efficiency cattle produce similar CH yield but different daily CH emissions. The 2 measurement techniques differ in estimating CH and CO emissions, partially because of differences in conditions (lower feed intakes of cattle while in chambers, fewer days measured in chambers) during measurement. We conclude that when intake of animals is known, the GEM system offers a robust and accurate means of estimating CH emissions from animals under field conditions.

Carbon balance in an agriculture-disturbed forested headwater stream in South China: Variations and environmental controls.