Atmospheric methane

About: Atmospheric methane is a research topic. Over the lifetime, 2034 publications have been published within this topic receiving 119616 citations.

Methane and Nitrous Oxide Emissions Reduced Following Conversion of Rice Paddies to Inland Crab-Fish Aquaculture in Southeast China.

Abstract: Aquaculture is an important source of atmospheric methane (CH4) and nitrous oxide (N2O), while few direct flux measurements are available for their regional and global source strength estimates. A parallel field experiment was performed to measure annual CH4 and N2O fluxes from rice paddies and rice paddy-converted inland crab–fish aquaculture wetlands in southeast China. Besides N2O fluxes dependent on water/sediment mineral N and CH4 fluxes related to water chemical oxygen demand, both CH4 and N2O fluxes from aquaculture were related to water/sediment temperature, sediment dissolved organic carbon, and water dissolved oxygen concentration. Annual CH4 and N2O fluxes from inland aquaculture averaged 0.37 mg m–2 h–1 and 48.1 μg m–2 h–1, yielding 32.57 kg ha–1 and 2.69 kg N2O–N ha–1, respectively. The conversion of rice paddies to aquaculture significantly reduced CH4 and N2O emissions by 48% and 56%, respectively. The emission factor for N2O was estimated to be 0.66% of total N input in the feed or 1.64 g ...

Trace gas exchange and climatic relevance of bog ecosystems, Southern Germany

Abstract: Natural mires accumulate organic substances continuously and act as carbon sinks. At a worldwide scale, the amount of carbon stored in peatlands represents about 20% of the total soil carbon stock, unless peatlands cover just 3% of the worlds land-surface. Drainage and peat cutting provoke the decomposition of the carbon pools and convert peatlands to carbon sources. Research on carbon-exchange and climatic relevance were up to now mainly focused on boreal and sub-arctic peatlands. Therefore, this project was initiated to fill a regional and thematic gap, studying trace gas exchange of natural, degraded and restored bog-ecosystems in the southern German mire belt in the forelands of the Bavarian Alps. The overall goal was to assess the carbon balance and the climatic relevance via trace gas exchange measurements and to clarify, if bog-restoration is a viable means for climate mitigation. For that purpose, a new closed chamber system was developed, as existing techniques had limitations to be applied in the frame of this study (chapter 2). The prominent properties of the chamber are the transparency and the cooling system, working without line connection. The temperature inside the chamber can be controlled to ± 1°C even on bright days. Therefore, photosynthesis is not disturbed and the measurement of the net ecosystem exchange within a small-scale mosaic of ecosystems is possible. Crosschecks with the eddy covariance technique revealed highly coincident flux-rates for CO2 (r2=0.94, 1:1 line). As prerequisite to assess the carbon balance and the climatic relevance of the ecosystems, the chamber allows sampling CH4 as well as N2O, parallel to CO2. Site selection led to a total of 12 sites with 36 plots as representative examples of the southern German bog-ecosystems in the forelands of the Bavarian Alps. The selected sites were dry former peat cut areas, drained-only bog heathlands, restored Sphagnum-lawns, restored moist bog heathlands, natural bog shrubs, natural Sphagnum-lawns, Eriophorum-hummocks and Scheuchzeria-Sphagnum hollows. This field based selection was post-hoc assessed in terms of site differentiation (chapter 3). Vegetation composition and site factors were analysed with multivariate ordination techniques in view of inspecting similari-ties between the sites. A canonical correspondence analysis (CCA) revealed a clear differentiation of the sites along a disturbance gradient, confirming the field based site selection. Gas exchange measurements for CO2, CH4 and N2O were done weekly to twice a week at these plots. The determined CO2 fluxes were used for the parameterisation of a NEE-model (chapter 4). NEE was modelled in 0.5 hours steps over the entire measurement year and the net ecosystem productivity (NEP) was integrated from the NEE curve, with the convention that negative values represent uptake to the system. As a result, former peat cut sites were detected to act as strong sources for carbon dioxide with mean emissions of 401.5 ± 47.5 g CO2-C m-2a-1 whereas natural sites were notable sinks (-71 ± 40.5 g CO2-C m-2a-1). Restored sites fell in between with 127 ± 47.3 g CO2-C m-2a-1 still acting as sources for carbon dioxide but reduced to 30% of the amount of the former peat cut sites. The NEP differentiated the sites along the disturbance gradient. NEP correlated significantly with environmental variables like electrical conductivity (r2=0.91), leaf area index (r2=0.87) and mean water-table (r2=0.84). Methane and nitrous oxide annual balances (chapter 5) do separate as well along the disturbance gradient. Maximum methane emissions were obtained at the natural Sphagnum-hollow (38.2 ± 2.2 g CH4-C m-2a-1), whereas the dry former peat cut areas were almost neutral in methane emissions. Restored sites were found in between (1.5 ± 0.2 – 7.1 ± 3.1 g CH4-C m-2a-1). Instant methane fluxes at the natural sites could be explained significantly with NEE (r2 0.53-0.68), representing the functional link between carbon dioxide uptake and methane production. The annual methane-balances could be explained with water-table (r2 0.54), quantity of aerenchymous leaves (r2 0.82), multiple linear regression of both fac-tors (r2 0.85) and finally best with NEP (r2 0.87). All these factors are functionally related to the production or emission of methane. Due to their low nutrient status and normally high water table, bog ecosystems show very small N2O emissions. Consequently only the dry former peat-cut areas had notable emissions rates (50 ± 47 - 168 ± 94 mg N2O-N m-2a-1). The carbon balance (chapter 6) was calculated as CO2-C balance minus the CH4-C balance. Carbon losses via DOC/DIC however, had to be estimated based on literature, as the complex hydrology of the sites did not allow for studying this export path. The carbon balance of the degraded sites was only slightly influenced by the methane emissions. At the natural sites, however, rising methane emissions led to significant differences between the carbon dioxide balance (-71 ± 40.5 g CO2-C m-2a-1) and the carbon balance (-45.6 ± 40.5 g C m-2a-1). The differences at the restored sites were significantly lower (127 ± 47.3 g CO2-C m-2a-1 to 137.6 ± 47.4 g C m-2a-1). The climatic relevance was calculated via the multiplication of the balances of all three gases with their corresponding global warming potential (GWP) differentiated for 100 years and 500 years timescale. At the 100 years timescale, all sites contributed to global warming. This is remarkable especially for the wet part of the natural sites, which acted as notable carbon sinks (-80.5 ± 37.3 g C m-2a-1) but heated the atmosphere with 77.5 ± 40.5 g CO2-C equivalents m-2a-1 (GWP-balance). This is an effect of the elevated methane emissions at the natural sites and the fact that methane holds a 21-times higher global warming potential than carbon dioxide. The degraded sites, however, contributed to global warming up to 465.6 ±71.1 g CO2-C eq. m-2a-1. Calculating the climatic relevance for the 500 years timescale, results in similar global warming effects of the de-graded sites (455.4 ± 70.3 g CO2-C eq. m-2a-1), whereas the wet natural sites shift in the long-term to mitigate global warming at a rate of –52.6 ± 37.6 g CO2-C eq. m-2a-1. The reason beeing the reduced global warming potential of methane for the long-term (5.6 times CO2) because of shorter lifetimes of methane in the atmosphere. Restoration of former peat cut sites contributes to climate mitigation with a reduction of 339.5 ± 53.3 g CO2-C m-2a-1 or 336.8 ± 54 g CO2-C g eq. m-2a-1 respectively. Restoration of the widespread drained-only bog heathlands leads still to climate mitigation in the range of 108.5 ± 53.3 g CO2-C m-2a-1 and 66.6 ± 55 g CO2-C g eq. m-2a-1. Bavaria published a climate protection programme with the overall goal to reduce the CO2 emissions to 80 Mio t per year. However, it is likely that a 3 Mio t gap in reaching this goal with technical measures exclusively will remain. Based on the above outlined climate mitigation effect of bog restoration together with the potential total area for restoration, the overall climate mitigation potential was calculated and divided by the per capita gap of the climate protection programme for the population in the mire belt. This leads to a range of 27 – 36 % for closing the per capita gap via the assessed restoration measures. Therefore, bog restoration can significantly contribute to the achievement of climate protection goals at a regional level. If Bavaria, however, targets to fulfil the stronger Kyoto goals, bog restoration can still help to meet 10 – 13% of the per capita commitments. The recently published Bavarian mire-development programme could serve as a suitable platform for the application of the synergistic goals of mire conservation and climate protection.

14CH4 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources

Abstract: The cause of a large increase of atmospheric methane concentration during the Younger Dryas–Preboreal abrupt climatic transition (~11,600 years ago) has been the subject of much debate. The carbon-14 ( 14 C) content of methane ( 14 CH 4 ) should distinguish between wetland and clathrate contributions to this increase. We present measurements of 14 CH 4 in glacial ice, targeting this transition, performed by using ice samples obtained from an ablation site in west Greenland. Measured 14 CH 4 values were higher than predicted under any scenario. Sample 14 CH 4 appears to be elevated by direct cosmogenic 14 C production in ice. 14 C of CO was measured to better understand this process and correct the sample 14 CH 4 . Corrected results suggest that wetland sources were likely responsible for the majority of the Younger Dryas–Preboreal CH 4 rise.

Methane and carbon dioxide evolution from subarctic fens

Abstract: Rates of net methane and carbon dioxide evolution from four subarctic fens over one summer ranged from 0 to 7 mmol CH4 m−2 d−1 and from 2 to 29 mmol CO2 m2 d−1. Average molar ratios of carbon dioxide to methane ranged from 3 to 10. Partially because of the high spatial variability in evolution rates, the temperature dependence of carbon dioxide was weak, but stronger for methane, with significant (P < 0.05) positive correlations at two sites, especially with peat temperatures. Annual flux of methane is estimated to be 0.1–0.6 g C m−2 which, although low compared to other wetlands, becomes a substantial atmospheric contribution when the large area occupied by subarctic peatlands is taken into account. Key words: Methane, carbon dioxide, peatlands, fens

Methane oxidation in landfill cover soils, as revealed by potential oxidation measurements and phospholipid fatty acid analyses

Abstract: Landfills account for ca. 10% of the annual global burden of atmospheric methane. Part of the efflux is mitigated by means of biological methane oxidation in the landfill covers. In this study, two types of landfill cover soils (mineral soil and sewage sludge) were compared with respect to methane emissions as well as potential methane oxidation capacity and the PLFA (phospholipid fatty acid) content of soil samples. Methane fluxes were lowest at a landfill site where wastes were covered with old sewage sludge. This site consumed atmospheric methane on most occasions. In incubated soil samples from the landfill cover composed of mineral soil, potential methane oxidation was most strongly correlated with the concentration of PLFA 18:1ω8, which is typical for type-II methanotrophic bacteria. In contrast, in samples from a landfill cover composed of fresh sewage sludge, methane oxidation was most strongly correlated with 16:1-PLFAs, indicating that type-I methanotrophs predominated, probably owing to nutritional conditions being more favourable in the sludge. The results also indicate that it takes a long time, i.e. several years, for methanotrophs to get well established in landfill cover soils.