Browsing by Subject "Methanemission"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Publication
    Biogenic Greenhouse Gas Emissions from Agriculture in Europe - Quantification and Mitigation
    (2002) Freibauer, Annette; Zeddies, Jürgen
    This dissertation analyses relevant potential mitigation strategies of biogenic greenhouse gases (GHGs) in the agriculture of the European Union (EU) in light of the Kyoto Protocol. It identifies where important sources and mitigation potentials are located and what uncertainty, environmental ancillary effects and costs are associated with them. Literature reviews are performed and methodologies for environmental assessment and GHG accounting are further developed. On this basis, GHG emissions are quantified and reduction potentials are assessed at European level. In 1995, European agriculture emitted 0.84 ± 0.29 Tg N2O, 8.1 ± 1.9 Tg methane (CH4) and 39 Tg ± 25 carbon dioxide (CO2), which adds up to 470 ± 80 Tg CO2-equivalents or 11% of the overall anthropogenic greenhouse gas emissions of the EU. The detailed methodology developed here adequately resolves regional specifics of agricultural conditions and reduces the methodological uncertainty in the estimates to half of the one in the official national inventories. European agricultural soils will at maximum sequester carbon in the order of 100 Tg a-1 CO2 over the coming years, which may also provide other environmental benefits. The biological potential of bioenergy in the EU allows to substitute for 400 to 800 Tg a-1 CO2-equivalents. From an environmental perspective, the use of perennials, especially of residues and woody biomass, is preferable to intensively grown annual crops. The biological potential for technical GHG reduction measures in EU agriculture is between 100 and 200 Tg a-1 CO2-equivalents. Promising measures promote the extensivation of arable cropping by reducing nitrogen inputs, technological innovation in animal husbandry, which is best accompanied by a further decline in animal numbers, as well as rewetting drained organic soils. Most measures will provide ancillary environmental benefits. Changing the socio-economic and political frame conditions may enhance the GHG mitigation potential.
  • Thumbnail Image
    Publication
    Carbon and nitrogen transformations in alpine ecosystems of the Eastern Alps, Austria
    (2007) Koch, Oliver; Kandeler, Ellen
    This thesis investigated net CH4 and net CO2 emissions from sites in the alpine region of the Eastern Alps, Austria. Four mature alpine sites (one dry meadow and three fen sites) were selected and the influence of abiotic (radiation, temperature, soil water conditions) and biotic (above-ground standing plant biomass) environmental controls on diurnal and seasonal emission patterns were studied. For a better understanding of the response of soil C- and N pools to global warming, the temperature sensitivity of activities involved in C- and N cycling were determined. The first part of the thesis dealt with net methane fluxes measured over a period of 24 months. During snow-free periods, average methane emissions of the fen sites ranged between 19 and 116 mg CH4 m-2 d-1. Mean emissions during snow periods were much lower, being 18 to 59% of annual fluxes. The alpine dry meadow functioned as a small methane sink during snow-free periods (-2.1 mg CH4 m-2 d-1 (2003); -1.0 mg CH4 m-2 d-1 (2004)). The diurnal and seasonal methane uptake of the dry meadow was positively related to soil temperature and negatively related to water-filled pore space (wfps). In the fen, the seasonal methane fluxes were related to soil temperature and groundwater table. The live above-ground standing plant biomass contributed to net methane fluxes only at those sites with higher water table positions. This study provided evidence that alpine fens acted as methane sources throughout the year, whereas an alpine meadow site acted as a net methane sink during snow-free periods. In the second part of the thesis the CO2 balance was estimated based on diurnal flux measurements and on the influence of photosynthetic active radiation (PAR), plant green area index (GAI), soil temperature and wfps. The daylight net ecosystem CO2 emission rate was influenced by PAR and GAI throughout snow-free seasons. The seasonal net CO2 emission rate at night was positively related to soil temperature, while low wfps reduced flux rates at the meadow and at the driest fen study site but reinforced carbon loss at the wetter fen sites. The daily average ecosystem net CO2 gain during snow-free periods at the meadow was 3.5 g CO2 m-2 d-1 and at the fen sites between 1.5 and 3.4 g CO2 m-2 d-1. The mean average daily CO2 emission during snow periods was low, being -0.9 g CO2 m-2 d-1 for the meadow and between -0.2 and -0.7 g CO2 m-2 d-1 for all fen sites. All sites function as significant annual net carbon sinks, with a net carbon gain from 50 to 121 g C m-2 a-1 (averaged over both years), irrespective of water balance. The results indicate that alpine fen sites, that have built up a large carbon stock in the past, are not expected to gain a further carbon surplus compared with meadows under the current climate. Temperature is important for regulating biological activities. The third part of the thesis focused on temperature sensitivity of soil C mineralization, N mineralization and potential enzyme activities involved in the C- and N cycle (ß-glucosidase, ß-xylosidase, N-acetyl-ß-glucosaminidase, tyrosine aminopeptidase, leucine aminopeptidase) over a temperature range of 0-30°C. The objective was to calculate Q10 values and relative temperature sensitivities (RTS) and to quantify seasonal (summer, autumn, winter) and site-specific factors. The Q10 values of C mineralization were significantly higher (average 2.0) than for N mineralization (average 1.7). The Q10 values of both activities were significantly negatively related to soil organic matter quality. In contrast, the chemical soil properties, microbial biomass and sampling date did not influence Q10 values. Analysis of RTS showed that the temperature sensitivity increased with decreasing temperature. The C- and N mineralization and potential aminopeptidase activities (tyrosine, leucine) showed an almost constant temperature dependence over 0-30°C. In contrast, ß-glucosidase, ß-xylosidase and N-acetyl-ß-glucosaminidase showed a distinctive increase in temperature sensitivity with decreasing temperature. Low temperature at the winter sampling date caused a greater increase in the RTS of all activities than in autumn and summer. Our results indicate a disproportion of the RTS for potential enzyme activities of the C- and N cycle and a disproportion of the RTS for easily degradable C compounds (ß-glucose, ß-xylose) compared with the C mineralization of soil organic matter. Thus, temperature may play an important role in regulating the decay of different soil organic matter fractions.
  • Thumbnail Image
    Publication
    Contribution of smallholder ruminant livestock farming to enteric methane emissions in Lower Nyando, Western Kenya
    (2018) Onyango, Alice Anyango; Dickhöfer, Uta
    The present study proposed some area-specific solutions and/or recommendations to common challenges hindering accurate estimation of enteric methane (CH4) emissions from sub-Saharan smallholder cattle systems. The results show that enteric CH4 from cattle systems in Kenya are an important contributor to agricultural greenhouse gases (GHG) and hence, needs close attention in the on-going process of developing Nationally Appropriate Mitigation Actions in the Kenyan livestock sector. However, the multi-functionality of animals in these systems should be considered in future in the assessment of emission factors (EF) and (emission intensities) EI. There appears to be great potential for reducing emissions, for example by improving animal husbandry, animal feeding and performance.
  • Thumbnail Image
    Publication
    Real-time in situ measurements of trace gases from agriculturally cultivated soils by means of laser spectroscopic techniques
    (2008) Hillebrand, Malte; Haas, Ulrich
    Two devices to study the exchange of climate relevant trace gases between arable cultivated soils and the atmosphere in the North China Plain are presented in this thesis. They are based on Tunable Diode Laser Photoacoustic Spectroscopy (TDL-PAS). These devices are capable of real-time in situ detection of trace gases. For methane a detection limit of 85 ppb and for ammonia of 111 ppb was achieved, respectively. For the field campaign at the experimental field Dongbeiwang (DBW) in Beijing it was necessary to optimize the instruments due to the harsh conditions in China, e.g. high variation in temperature, high humidity and particulate matter emissions. This included accurate thermally stabilization of the system as well as long-term stability of the laser diode and the possibility of unattended operation over a period of several days. These prerequisites were fulfilled and evaluated in Germany before the devices were brought to China for the field campaign in the years 2006 and 2007. Additionally, mobile closed chambers for the trace gas exchange measurements were designed in Germany. They consisted of two parts: One frame installed permanently in the soil, therein agricultural crops could be planted, and a hood placed on it during the measurement and removed afterwards again. Altogether seven frames made from stainless steel were constructed by a company located in Beijing. Three hoods of different heights (250, 500 and 1000 mm) were made from 8 mm colorless Plexiglas and were built by a German company. The innovation of this design was the possibility to insert up to eight cooling packs that cooled down the enclosed air in the chambers by mixing it via two fans. By comparing measurements with and without applying cooling packs it was shown that the temperature difference between both situations was increasing up to 10 K. According to ambient air temperature measurements the test also showed that by applying cooling packs the temperature of the enclosed air could be adapted close to ambient conditions. After installation of the closed chambers in DBW a test checking the gas tightness had to be performed. With this test leakages of the frames, hoods and tubes should be discovered. This was done by injection of 2 ml ethane into the closed chambers and studying the concentration decrease within one hour of closure time. For this test the permanently installed gas chromatograph in the measurement container in DBW was used, connected by Teflon tubes to the closed chambers. All closed chambers showed leakages lower than 10% and therefore could be considered as tight. For methane measurements the chambers were operated in the dynamic mode, so the air inside of the chamber was circulated through the TDL-PA system and pumped back into the chamber. The increase or decrease in methane concentration with time was determined and flux rates were calculated. The obtained data confirmed that the soil in DBW, a Calcaric Cambisol according to FAO classification, could be considered as a methane sink. The exchange rate ranged from ?0.17 to ?3.33 mg CH4-C m-² d-¹ for winter wheat and from ?0.68 to ?2.07 mg CH4-C m-²; d-¹ for bare soil. For summer maize the exchange rate was slightly lower and ranged from ?0.51 to ?1.0 mg CH4-C m-² d-¹ and from ?0.53 to ?1.14 mg CH4-C m-² d-¹ for the control plot. Due to the fact that elevated methane concentrations at daybreak were detected during the exchange measurements at the plots planted with winter wheat as well as at the control plot a diurnal variation in methane concentration was assumed. To verify and quantify this diurnal variation in methane concentration at DBW, one plot was selected for a 24 hour measurement campaign. During this measurement campaign ambient air methane concentrations of up to 22 ppm were observed during nighttime, which was elevenfold the normal concentration. Because the previous exchange measurements revealed that methane was not emitted by the soil it must originated from somewhere else. After the 24 hour measurement campaign the ambient air methane concentrations in DBW as well as at other places in the vicinity of DBW were studied to detect the source of the methane emissions. For that purpose an ultrasonic anemometer for wind direction and wind speed measurement was combined with the TDL-PA system. A diurnal variation with maximum methane concentrations of about 40 ppm during nighttime and early morning and minimum concentrations of about 1.4 ppm during the afternoon were detected in DBW. Research conducted at the campus of the CAU, 3.2 km south of DBW, showed a similar pattern. These results confirmed the urban heat island effect where stable atmospheric layering dominates during the night and a mixing layer dominates during daytime. According to literature the height of this atmospheric boundary layer in Beijing in autumn was of 1 km thickness during daytime and of 200 ? 400 m during nighttime. Moreover the high methane concentrations in the night verified the assumption of a methane emission source in the vicinity of DBW and the CAU. The search for a potential emission source revealed a landfill approximately 6 km north-west of the CAU as well as 5.5 km west of DBW. Measurements conducted at the landfill site itself showed a diurnal methane emission pattern as well, with maximum concentrations up to 450 ppm during nighttime and minimum concentrations of about 10 ppm during daytime.