1 / 45

The Global Methane Cycle

The Global Methane Cycle. Methane. CH 4 Colorless gas Component of the atmosphere Main component of natural gas CH 4 + 2O 2 → CO 2 + 2H 2 0 . Why is methane important?. Clean fuel source It is a powerful greenhouse gas It removes Hydroxyls from the troposphere

lotus
Télécharger la présentation

The Global Methane Cycle

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Global Methane Cycle

  2. Methane • CH4 • Colorless gas • Component of the atmosphere • Main component of natural gas • CH4 + 2O2→CO2 + 2H20

  3. Why is methane important? • Clean fuel source • It is a powerful greenhouse gas • It removes Hydroxyls from the troposphere • Affects concentrations of water vapor and ozone in the stratosphere • Used in the industrial production of hydrogen, methanol, acetic acid, and acetic anhydride

  4. Methane as a fuel source • Used as a fuel source for electricity generation, heating, and cooking • Methanol is used in vehicles • Heat of combustion is about 802 kJ/mol • Highest heat to weight ratio • Produces the least CO2 per unit of heat

  5. How much methane is there? • ~350 ppb 18,000 years ago • Today atmospheric levels are ~1800 ppb and rising • The most abundant greenhouse gas after CO2 and H2O vapor • Most abundant trace gas in the atmosphere

  6. Where is methane from? • It is produced by organisms and geological processes • Livestock produces 37% of all human-induced methane • Most is released from wetlands in the northern hemisphere and tropics

  7. Methane is cycled • Certain organisms and geological processes produce methane • Other organisms and processes use methane and release new products • Several organisms and processes are involved • The methane cycle is part of the larger carbon cycle

  8. Carbon cycle diagram

  9. Sources: Natural Wetlands Termites Oceans Hydrates & Clathrates

  10. Wetlands • Produces 225 Tg per year. • 50% of wetlands are peat rich. • Produced by methanogenic bacteria decomposing organic materials in anaerobic environments. • CH4 produced in sediments are diffused to the surface via the water column, gas bubbles, or plants. • C6H12O6 -> 3CO2 + 3CH4 • Massive amounts of CH4 trapped in permafrost could be released if temperatures rise.

  11. Termites • Produces 20 Tg per year • Concentrated mostly in grasslands or forests • Produced in the breakdown of cellulose by CH4 oxidizing bacteria

  12. Oceans • Produces 15 Tg per year • Sources are poorly known. • Coastal areas have higher but more variable concentrations. • Produced by seepage areas in seabed with organic rich nutrients.

  13. Hydrates • Produces 10 Tg per year • CH4 Hydrates are ridgid water cages surrounding CH4 molecules. • Mostly on the continental shelf of all latitudes. • Hydrate stability requires high pressures and cold temperatures. Most hydrates occur at depths and regions insulated from climate change. • Climate warming would lead to destabilization of hydrates and release CH4 molecules.

  14. Sources: Anthropogenic • Rice Cultivation • Fossil Fuels • Biomass Burning • Landfills

  15. Rice Cultivation • Produces 100 Tg per year • Production has increased over 40% since the 1980’s. • Produced by anaerobic consumption of organic material by methanogenic bacteria

  16. Domestic Animals • Produces 115 Tg per year • 75% are produced from cows • Produced from fermentation of carbohydrates in the rumen. Microbes in the rumen are capable of breaking down cellulose. • Quanity & Quality of feed, plus weight, age, activity level, and species affect how much CH4 is produced.

  17. Fossil Fuels • Produces 110 Tg per year • Coal Gas and Natural Gas consist almost entirely of methane. • Fossil Fuel sources are coal mining as well as exploration, production, transmissions.

  18. Biomass Burning • Produces 40 Tg per year • CH4 is released when vegetation is burned. • Amount produced depends on the burning technology, temperature, moisture and carbon content in the vegetation.

  19. Landfills • Produces 40 Tg per year • Decomposition of biodegradable organic material in landfills produces CO2 and CH4.

  20. Sinks Losses of CH4 occur in lithosphere and the atmosphere Lithosphere: Dry soil oxidation Atmosphere: Trophospheric reactions with OH and losses to the stratosphere

  21. Dry Soil Oxidation • A loss of 30 Tg per year • Can act as an sink for both atmospheric CH4 and CH4 produced in deeper soil layers. • Methanotrophs use CH4 as a source of carbon in a process called methane oxidation • Methanotrophs exist in two forms: 'high capacity - low affinity' methanotrophs ’low capacity - high affinity' methanotrophs Changes in land use practices, better fertilizer application, and land conversion may help prevent the loss of methane sinks.

  22. Tropospheric Reactions With OH • A loss of 510 Tg per year • The most dominant form of CH4 loss. • OH + CH4 -> CH3 + H2O • CH4 is removed when it reacts with the hydroxyl radical OH. This happens when cosmic rays strike a water vapor molecule. • Hydroxyl Radicals are considered the “Detergent” of the atmosphere because they react with many pollutants.

  23. Losses To The Stratosphere • A loss of 40 Tg per year • Plays a minor role in removing CH4 from the atmosphere • CH4 is loss to the stratosphere when it reacts with OH, Cl and O(1D) • The stratosphere is very dry and any water vapor produced from methane oxidation becomes a greenhouse gas itself.

  24. General Facts about Methane • Known as a ‘well-mixed greenhouse gas’ because of long lifetime so it is able to evenly distribute in atmosphere • More potent than CO2, but concentration of CO2 is higher so CO2 has greater effect on global warming -Control of methane emissions turns out to be a more powerful lever to control global warming than anticipated

  25. Effects on the Environment • Methane is a greenhouse gas ->absorbs heat in the atmosphere->Increase in temperature • Since Industrial Revolution, atmospheric methane concentration has doubled • Contributes about 20% towards the greenhouse effect, second to CO2

  26. Concentration of Methane over time

  27. Controversy • Levels of Greenhouse gases can be determined by: -measuring level of gases after mixing with other gases in the atmosphere (official IPCC) OR -measuring level of gases before entering atmosphere.

  28. Prevention for the Future • Methane to Market (United States, the UK, China, Russia, Brazil, India, Italy, Japan, Australia and Nigeria) Goal: To recover Methane and use it as clean energy.

  29. Federal Clean Air Act Collection of methane gas from landfills and treated • Processing manure using anaerobic digesters making methane available for conversion to useful energy • New rice harvesting method, reduce methane gas, increase yield

  30. Methane Cycling Microbes

  31. Methanogenesis - The Big Picture Why is this process interesting? • Terminus of anaerobic food chain. • Prevents sequestering of large amts or organic material in anaerobic ecosystems. • Potential natural gas source. • Methanogens are the most important CO2- reducing prokaryotes, but are also a source of greenhouse gas (CH4).

  32. Methanogenesis within the Carbon Cycle. Water column sediments

  33. Methanogenesis: The Process Overall Reaction: 4 H2 + H+ + HCO3- CH4 + 3H2O

  34. And who are these? • METHANOGENS • Archaea, ubiquitous in highly reducing habitats, also found in some “oxic” habitats • Obligate anaerobes • H2 + CO2 --> methane (CH4) • Autotrophic (fix CO2), chemolithotrophic (use inorganic H2 as e- donor) • Some use endproducts of fermentation (acetate, etc.) • Some important genera: Methanococcus, Methanosarcina • Capable of using elemental Sulfur as a terminal e- acceptor (anaerobic respiration - sulfur reduction) • METHANOTROPHS • Bacteria • Aerobes • Utilize methane: • CH4 + O2 --> CO2 + H2O • Rxn happens at interface btwn anoxic and oxic layers of soil (as CH4 diffuses up). • Genus: Methylomonas

  35. Phylogeny of Methanogens

  36. The Methanotrophs

  37. Cool and current studies A new biogeochemical cycling pathway couples anaerobic methane oxidation to denitrification. (Nature; vol. 440, 04/06). • Freshwater sediments receive high loads of anthropogenic NO3- and CH4. • Theoretically microbes should be able to use NO3-/NO2- to anaerobically oxidize CH4, but prior to this report it has not been shown. • This study showed direct, anaerobic oxidation of methane coupled to denitrification in the complete absence of O2. CH4 + NO3-/NO2- + H+ ---> CO2 + N2 + H2O • consortium consisted of two microbes: an uncultured bacteria and an archaea related to marine methanotrophic Archaea. Relevance: • new pathways fill in holes in our understanding of global biogeochemical cycling.

  38. Methanogens on Mars? FEMS Micro. Ecol. (2007) Greenland Ice Sheet • 10 ppbv CH4 on mars, estimated 300 tons lost/year - 270 tons/year must be generated to offset loss. • Is this biogenic or abiogenic methane? • Metabolic rates of methanogens in extreme cold on Earth can be used to estimate metabolic rates and cell densities of martian methanogens.

  39. Conclusions • Methane is the simplest hydrocarbon • Methane is a clean fuel source • Methane is a powerful greenhouse gas • Methane is part of the carbon cycle

  40. Conclusions • The major reservoirs of CH4 are fossil fuel reservoirs, hydrates and Clathrates, and the atmosphere • Wetlands are the dominant natural source of CH4 • Domestic animals are the largest anthropogenic source of CH4 • The Hydroxyl Radical OH, is the dominant form of CH4 loss. • There has been an increase in terrestrial sources and a decrease in sinks, leading to excess CH4 in the atmosphere

  41. Conclusions • Reducing Methane will have a stronger influence in reduce Greenhouse effect • ‘Methane To Market’ and ‘Federal Clean Air Act’ hopes to reduce Methane output • New agriculture and use of anaerobic digesters also reduce Methane output

  42. Conclusions • The methane cycle is composed of two groups: methanogens (produce methane) and methanotrophs (consume methane). • Methanogenesis is carried out anaerobically by Archaea, methanotrophy is carried out aerobically by bacteria. • Methanogens are ubiquitous in anoxic environments (wetlands, sediments, etc.) as well as some oxic ones.

  43. REFERENCES • Madigan, Martinko, and Parker. 1997. Brock Biology of Microorganisms. 8th ed. Prentice-Hall, New Jersey. • Stanier, R.Y., Ingraham, J.L., Wheelis, M.L., and Painter, P.R. 1986. The Microbial World. 5th ed. Prentice-Hall, New Jersey. • Strous, M. et al. 2006. A microbial consortium couples anaerobic methane oxidation to denitrification. Nature, 440:918-921. • Price, P.B. 2007. Microbial life in glacial ice and implications for a cold origin of life. FEMS Microbiol. Ecol. 59:217-231. • http://www.newscientist.com/article.ns?id=mg18725124.500 • http://www.meteor.iastate.edu/gcp/studentpapers/1996/atmoschem/brockberg.html • http://www.epa.gov/methane/sources.html • http://www.ghgonline.org/methanesinksoil.htm • http://www.igac.noaa.gov/newsletter/21/methane_sink.php • http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16827 • http://www.grida.no/climate/ipcc_tar/wg1/134.htm#4211

  44. References • http://www.scienceagogo.com/news/20050625005443data_trunc_sys.shtml • http://www.ace.mmu.ac.uk/eae/Global_Warming/Older/Methane.html • http://egov.oregon.gov/ENERGY/RENEW/Biomass/Environment.shtml • http://www.ens-newswire.com/ens/jul2005/2005-07-19-01.asp

More Related