Greenhouse gas emissions from different wetlands during the snow-covered season in Northeast China

Global warming will increase the greenhouse gas (GHG) fluxes of permafrost regions. However, little is known about the difference in GHG fluxes among different types of permafrost regions. In this study, we used the static opaque chamber and gas chromatography techniques to determine the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in predominantly continuous permafrost (PCP), predominantly continuous and island permafrost (PCIP), and sparsely island permafrost (SIP) regions during the growing season. The main factors causing differences in GHG fluxes among three types of permafrost regions were also analyzed. The results showed mean CO2 fluxes in SIP were significantly higher than that in PCP and PCIP, which were 342.10 ± 11.46, 105.50 ± 10.65, and 127.15 ± 14.27 mg m-2 h-1, respectively. This difference was determined by soil temperature, soil moisture, total organic carbon (TOC), nitrate nitrogen (NO3--N), and ammonium nitrogen (NH4+-N) content. Mean CH4 fluxes were -26.47 ± 48.83 (PCP), 118.35 ± 46.93 (PCIP), and 95.52 ± 32.86 μg m-2 h-1 (SIP). Soil temperature, soil moisture, and TOC content were the key factors to determine whether permafrost regions were CH4 sources or sinks. Similarly, PCP behaved as the sink of N2O, PCIP and SIP behaved as the source of N2O. Mean N2O fluxes were -3.90 ± 1.71, 0.78 ± 1.55, and 3.78 ± 1.59 μg m-2 h-1, respectively. Soil moisture and TOC content were the main factors influencing the differences in N2O fluxes among the three permafrost regions. This study clarified and explained the differences in GHG fluxes among three types of permafrost regions, providing a data basis for such studies.

IntroductionFarmlands are key sources of greenhouse gas (GHG) emissions, which are susceptible to changes in precipitation regimes. The soils of seasonal fallow contribute approximately half of annual GHG emissions from farmlands, but the effect of precipitation frequency on soil GHG emissions from seasonal fallow croplands remains virtually unknown.Materials and MethodsWe conducted a microcosm study to evaluate the response of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from typical paddy and upland soils to the changes in watering frequency simulating precipitation scenarios of subtropical regions during seasonal fallow. We also analyzed changes of soil properties and biotic characteristics associated with GHG emissions, including abundances of soil denitrifiers (nirK, nirS, nosZI and nosZII genes), methanotrophs (pmoA gene) and methanogens (mcrA gene) to altered watering frequency.ResultsIncreased watering frequency led to overall increases in soil N2O and CO2 fluxes compared with low frequency. Compared with low frequency, high watering frequency decreased CH4 flux from the paddy soil by 3.5 times, while enhanced CH4 flux from the upland soil by 60%. Furthermore, the increased watering frequency had positive effects on cumulative N2O and CO2 fluxes from the upland soil, whereas no similar trend was observed for the paddy soil. Hierarchical partitioning analyses showed that N2O fluxes from the paddy soil were mostly related to nitrogen availability, and mcrA gene abundance had more than 90% of relative independent effects on CH4 and CO2 fluxes from the paddy soil. For the upland soil, nosZ (60.34%), pmoA (53.18%) and nir (47.07%) gene abundances were important predictors of N2O, CH4 and CO2 fluxes, respectively.ConclusionOur results demonstrate that increased watering frequency facilitates GHG emissions by changing soil properties and functional gene abundances. These findings provide new insights into GHG fluxes from seasonal fallow croplands in response to altered precipitation patterns.

Dry and wet periods determine stem and soil greenhouse gas fluxes in a northern drained peatland forest

Rivers play an important role in greenhouse gas emissions. Over the past decade, because of global urbanization trends, rapid land use changes have led to changes in river ecosystems that have had a stimulating effect on the greenhouse gas production and emissions. Presently, there is an urgent need for assessments of the greenhouse gas concentrations and emissions in watersheds. Therefore, this study was designed to evaluate river-based greenhouse gas emissions and their spatial-temporal features as well as possible impact factors in a rapidly urbanizing area. The specific objectives were to investigate how river greenhouse gas concentrations and emission fluxes are responding to urbanization in the Liangtan River, which is not only the largest sub-basin but also the most polluted one in Chongqing City. The thin layer diffusion model method was used to monitor year-round concentrations of pCO2, CH4, and N2O in September and December 2014, and March and June 2015. The pCO2 range was (23.38±34.89)-(1395.33±55.45) Pa, and the concentration ranges of CH4 and N2O were (65.09±28.09)-(6021.36±94.36) nmol·L-1 and (29.47±5.16)-(510.28±18.34) nmol·L-1, respectively. The emission fluxes of CO2, CH4, and N2O, which were calculated based on the method of wind speed model estimations, were -6.1-786.9, 0.31-27.62, and 0.06-1.08 mmol·(m2·d)-1, respectively. Moreover, the CO2 and CH4 emissions displayed significant spatial differences, and these were roughly consistent with the pollution load gradient. The greenhouse gas concentrations and fluxes of trunk streams increased and then decreased from upstream to downstream, and the highest value was detected at the middle reaches where the urbanization rate is higher than in other areas and the river is seriously polluted. As for branches, the greenhouse gas concentrations and fluxes increased significantly from the upstream agricultural areas to the downstream urban areas. The CO2 fluxes followed a seasonal pattern, with the highest CO2 emission values observed in autumn, then successively winter, summer, and spring. The CH4 fluxes were the highest in spring and the lowest in summer, while N2O flux seasonal patterns were not significant. Because of the high carbon and nitrogen loads in the basin, the CO2 products and emissions were not restricted by biogenic elements, but levels were found to be related to important biological metabolic factors such as the water temperature, pH, DO, and chlorophyll a. The carbon, nitrogen, and phosphorus content of the water combined with sewage input influenced the CH4 products and emissions. Meanwhile, N2O production and emissions were mainly found to be driven by urban sewage discharge with high N2O concentrations. Rapid urbanization accelerated greenhouse gas emissions from the urban rivers, so that in the urban reaches, CO2/CH4 fluxes were twice those of the non-urban reaches, and all over the basin N2O fluxes were at a high level. These findings illustrate how river basin urbanization can change aquatic environments and aggravate allochthonous pollution inputs such as carbon, nitrogen, and phosphorus, which in turn can dramatically stimulate river-based greenhouse gas production and emissions; meanwhile, spatial and temporal differences in greenhouse gas emissions in rivers can lead to the formation of emission hotspots.

Agro-technologies for greenhouse gases mitigation in flooded rice fields for promoting climate smart agriculture

Three years of CO2, CH4 and N2O fluxes from different sheepfolds in a semiarid steppe region, China

The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2, CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63 –386.36 mg/(m•h), CH4 uptake fluxes of 0.113–0.023 mg/(m•h) and N2O fluxes of –1.68 –19.90 μg/(m•h). Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes. Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.

Forest soils are recognized as sources and sinks of greenhouse gases (GHG) (CO2, CH4, N2O), but there are limited data quantifying the magnitude of GHG fluxes at the soil-atmosphere interface across a range of landscape hydrogeomorphic conditions. In our study, GHG fluxes were measured in a forested watershed across a range of hydrogeomorphic locations (wetlands, hillslopes, riparian zones, etc) and evaluated in relation to temperature, antecedent flow conditions, and stream chemistry to help develop strategies to scale GHG emissions from the point scale to the watershed scale. Mean study period CO2 fluxes (0.61 to 2.89 gCm-2d-1) were positive at all sites, with larger fluxes occurring in well-drained soils. Negative fluxes (CH4 sinks) were found at the hillslope and lowland sites, while the wetland was a large source of CH4 emissions at the watershed scale. Mean CH4 fluxes ranged from -2.53 to 330.34 mgCm-2d-1. Nitrous oxide fluxes were low relative to other GHG fluxes (in terms of CO2 equivalent) and ranged between -0.72 to 0.70 mgNm-2d-1. Although carbon dioxide fluxes were positively correlated to soil temperature at all locations, CH4 and N2O fluxes were not significantly related to temperature, antecedent flow conditions, or stream chemistry at the watershed scale. However, strong differences in CO2 and CH4 fluxes related to landscape geomorphology were observed, and exceeded the magnitude of seasonal variations for CO2 and CH4 fluxes, suggesting that landscape hydrogeomorphology was likely a stronger predictor of GHG fluxes at the watershed scale than temperature and stream chemistry variables, at least within the confine of one watershed. In lieu of statistical approaches relying on environmental variables to predict GHG fluxes at the watershed scale, geomorphological approaches, potentially coupled with seasonal comparisons of GHG fluxes in each land class, might therefore be a promising research avenue to provide solid watershed wide estimates of GHG fluxes.

Water table management with controlled drainage and subsurface-irrigation (SI) has been identified as a Beneficial Management Practice (BMP) to reduce nitrate leaching in drainage water. It has also been shown to increase crop yields during dry periods of the growing season, by providing water to the crop root zone, via upward flux or capillary rise. However, by retaining nitrates in anoxic conditions within the soil profile, SI could potentially increase greenhouse gas (GHG) fluxes, particularly N2O through denitrification. This process may be further exacerbated by high precipitation and mineral N-fertilizer applications very early in the growing season. In order to investigate the effects of water table management (WTM) with nitrogen fertilization on GHG fluxes from corn (Zea mays) agro-ecosystems, we conducted a research study on a commercial farm in south-western Quebec, Canada. Water table management treatments were: free drainage (FD) and controlled drainage with subsurface-irrigation. GHG samples were taken using field-deployed, vented non-steady state gas chambers to quantify soil CO2, N2O and CH4 fluxes weekly. Our results indicate that fertilizer application timing coinciding with intense (≥24 mm) precipitation events and high temperatures (>25 °C) triggered pulses of N2O fluxes, accounting for up to 60% of cumulative N2O fluxes. Our results also suggest that splitting bulk fertilizer applications may be an effective mitigation strategy, reducing N2O fluxes by 50% in our study. In both seasons, pulse GHG fluxes mostly occurred in the early vegetative stages of the corn, prior to activation of the subsurface-irrigation. Our results suggest that proper timing of WTM mindful of seasonal climatic conditions has the potential to reduce GHG emissions.

With global warming, the large amount of greenhouse gas emissions released by permafrost degradation is important in the global carbon and nitrogen cycle. To study the feedback effect of greenhouse gases on climate change in permafrost regions, emissions of CO2, CH4, and N2O were continuously measured by using the static chamber-gas chromatograph method, in three forest soil ecosystems (Larix gmelinii, Pinus sylvestris var. mongolica, and Betula platyphylla) of the Daxing’an Mountains, northeast China, from May 2016 to April 2018. Their dynamic characteristics, as well as the key environmental affecting factors, were also analyzed. The results showed that the flux variation ranges of CO2, CH4, and N2O were 7.92 ± 1.30~650.93 ± 28.12 mg·m−2·h−1, −57.71 ± 4.65~32.51 ± 13.03 ug·m−2·h−1, and −3.87 ± 1.35~31.1 ± 2.92 ug·m−2·h−1, respectively. The three greenhouse gas fluxes showed significant seasonal variations, and differences in soil CO2 and CH4 fluxes between different forest types were significant. The calculation fluxes indicated that the permafrost soil of the Daxing’an Mountains may be a potential source of CO2 and N2O, and a sink of CH4. Each greenhouse gas was controlled using different key environmental factors. Based on the analysis of Q10 values and global warming potential, the obtained results demonstrated that greenhouse gas emissions from forest soil ecosystems in the permafrost region of the Daxing’an Mountains, northeast China, promote the global greenhouse effect.

The study characterized the temporal and spatial variability in greenhouse gas (GHG) fluxes (CO2, CH4, and N2O) between December 2020 and November 2021 and their regulating drivers in the subtropical wetland of the Indian Himalayan foothill. Five distinct habitats (M1-sloppy surface at swamp forest, M2-plain surface at swamp forest, M3-swamp surface with small grasses, M4-marshy land with dense macrophytes, and M5-marshy land with sparse macrophytes) were studied. We conducted in situ measurements of GHG fluxes, microclimate (AT, ST, and SMC(v/v)), and soil properties (pH, EC, N, P, K, and SOC) in triplicates in all the habitat types. Across the habitats, CO2, CH4, and N2O fluxes ranged from 125 to 536mgm-2h-1, 0.32 to 28.4mgm-2h-1, and 0.16 to 3.14mgm-2h-1, respectively. The habitats (M3 and M5) exhibited higher GHG fluxes than the others. The CH4 flux followed the summer > autumn > spring > winter hierarchy. However, CO2 and N2O fluxes followed the summer > spring > autumn > winter. CO2 fluxes were primarily governed by ST and SOC. However, CH4 and N2O fluxes were mainly regulated by ST and SMC(v/v) across the habitats. In the case of N2O fluxes, soil P and EC also played a crucial role across the habitats. AT was a universal driver controlling all GHG fluxes across the habitats. The results emphasize that long-term GHG flux monitoring in sub-tropical Himalayan Wetlands has become imperative to accurately predict the near-future GHG fluxes and their changing nature with the ongoing climate change.

Greenhouse gas (GHG) flux from wetland systems, both in their natural state and following drainage, has not been well accounted for in the carbon accounting process. We review GHG production from both natural and drained wetlands, and estimate the likely GHG emissions from these systems in Australia. Only a small number of studies have quantified GHG emissions from undisturbed Australian wetland environments. Consequently, in order to estimate GHG flux for Australia, it was necessary to collate data collected overseas from similar climatic zones. Using this approach, it appears that undisturbed, vegetated wetlands in Australia are likely to be net GHG sinks, with the greatest rates of sequestration occurring in mangrove ecosystems (–2669 g CO2-e/m2.year) where biomass production is high but CH4 emissions are limited by salinity. The uncertainty surrounding these values is high, however, due to (a) the low number of measurements from Australia, (b) the low number of measurements for CO2 flux, and (c) the low number of studies where all GHGs have been measured concurrently. It was estimated that the drainage of melaleuca and mangrove forest wetlands in Australia would turn them from carbon sinks into carbon sources, and that in the first 50 years since drainage, this has increased global warming potential by 1149 Tg CO2-e or 23 Tg CO2-e/year. This is significant given that GHG emissions due to land-use change in 2007 totalled 77.1 Tg CO2-e. However, data surrounding the area of wetlands drained, carbon stocks in drained wetlands, and the effect of drainage on CH4 and N2O flux are limited, making the uncertainty surrounding these estimates high. Further study is clearly required if Australia wishes to accurately incorporate wetland systems into national carbon and greenhouse gas accounting budgets.

In the climate change scenario, studying greenhouse gases (GHG) emissions and measures of mitigation in the Caatinga biome are strategic and may provide a basis for mitigation plans. This study aimed to evaluate the soil CO2, CH4 and N2O fluxes, as well as determining an annual baseline for GHG emissions, in a reference site of silvopastoral production system in the Brazilian semiarid region, in order to provide subsidies for future studies on GHG emissions mitigation. The GHG fluxes were monitored over one year, in a buffel grass pasture and in grazed and native Caatinga areas, which are components of a long-term silvopastoral system. The CO2 fluxes ranged from -19.98 to 179.12 mg m-2 h-1 of CO2-C, CH4 fluxes from -76.21 to 113.87 µg m-2 h-1 of CH4-C, N2O fluxes from -1,043.12 to 471.37 µg m-2 h-1 of N2O-N and the soil moisture was the main factor limiting the GHG fluxes. The total emissions converted to CO2-equivalent in the anthropized areas were lower than in the native area (65 % for the buffel grass pasture and 741 % for the grazed Caatinga). Therefore, it is possible to afrm that the GHG soil emissions from grazed areas in the Caatinga biome are not as high as in the native Caatinga, what is an important indication of the environmental sustainability of the evaluated silvopastoral system.

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.

Rising concerns about global warming as a consequence of increased anthropogenic greenhouse gas emissions have markedly strengthened scientific, political, and even public interest in issues surrounding human-induced climate change. This has resulted in fundamental economic and ecologic debates