Swamp Gas
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Marsh gas, also known as swamp gas or bog gas, is a mixture primarily of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
and smaller amounts of
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
,
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, and trace
phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
that is produced naturally within some geographical
marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
es,
swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s, and
bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...
s. The surface of marshes, swamps, and bogs is initially
porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
vegetation that rots to form a crust that prevents
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
from reaching the organic material trapped below. That is the condition that allows
anaerobic digestion Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the ferm ...
and
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
of any
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
or
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
matter, which then produces methane. The trapped methane can escape through any of three main pathways: by the diffusion of methane molecules across an air–water interface, by bubbling out of water in a process known as
ebullition Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. Th ...
, or through plant-mediated transport.


Methane formation

Methane is the primary gas that makes up the product colloquially known as "marsh gas". Much of the biogenic methane produced in nature is derived from either
acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...
cleavage or by the hydrogen reduction of carbon dioxide. Methane can also be produced by
methanogen Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are com ...
s,
archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
that produce methane under
anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
conditions, in a process known as
methanogenesis Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group ...
. Methanogenic genera ''
Methanosarcina ''Methanosarcina'' is a genus of euryarchaeote archaea that produce methane. These single-celled organisms are known as anaerobic methanogens that produce methane using all three metabolic pathways for methanogenesis. They live in diverse envi ...
'' are common in marsh environments. They are both known to stimulate methane production in aquatic muds and use
acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...
,
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
, and
trimethylamine Trimethylamine (TMA) is an organic compound with the formula N(CH3)3. It is a colorless, hygroscopic, and flammable tertiary amine. It is a gas at room temperature but is usually sold as a 40% solution in water. (It is also sold in pressurized ...
as substrates for methane production.


Escape routes

Global wetlands are one of the largest sources of
atmospheric methane Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising. The 20-year glob ...
. This methane, which is produced by the decomposition of organic matter in an
anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
environment, escapes through either
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
, a process that occurs mostly at night, ebullition, or plant-mediated transportation. The diffusive process is controlled by the passage of gas across the air–water interface. The diffusion can be accelerated and intensified by
upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...
, such as the motion from turbulent eddies, and cooling processes. At night, heat is emitted from the water surface by radiation. The colder surface water sinks, pushing the warmer surface water out and forming eddies. These eddies circulate the dissolved methane throughout the water column and increase the methane flux to the atmosphere. This process is called hydrodynamic transport, and it accounts for more than half of nighttime methane fluxes as well as 32% of annual methane emissions from wetland environments. Ebullition, also known as bubbling, is a type of one-way transport of gases from nutrient rich sediments, to the water column, and then to the atmosphere. It is a major mechanism for gas exchange in freshwater and coastal marine ecosystems and is known to peak during the daytime and at warm temperatures. It has been reported that ebullition is responsible for 45% of the annual methane flux for fresh water marshes and that it is more important in the summer months during the daytime and can also be triggered by increased wind. One of the most common species of grass in marsh environments is ''
Spartina ''Spartina'' is a taxon of plants in the grass family, frequently found in coastal salt marshes. Its species are commonly known as cordgrass or cord-grass, and are native to the coasts of the Atlantic Ocean in western and southern Europe, north ...
''. These spartina and other common marsh grasses use a gas transport system found in the stems and roots of the plants. The gas transport system works by
gaseous diffusion Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride (UF6) through semipermeable membranes. This produces a slight separation between the molecules containing uranium-235 (235U) and uranium-2 ...
that occurs through the leaf blades and then moves down into the furthest tips of the plant roots. This transport system is sufficient to supply all of the aerobic respiratory needs of the grass roots and also helps to aerate the surrounding mud.


Environmental impact

Over the past century, more than 50% of the original tidal
salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated ...
habitats in the U.S. have been lost. The majority of this loss can be directly accounted for by human activity. Direct human impacts that negatively impact salt marshes include: dredging, spoil dumping, grid ditching, canal cutting, leveeing, and salt hay farming. Indirect impacts, such as land reclamation projects and dam construction, which usually occur over a longer period of time than the direct impacts, can lead to even more damages that affect tidal flooding at the marsh surface, cause changes to wetland drainage, shoreline retreat, and reduce vertical marsh accretion rates. Changes in
eustatic sea level The eustatic sea level is the distance from the center of the earth to the sea surface. An increase of the eustatic sea level can be generated by decreasing glaciation, increasing spreading rates of the mid-ocean ridges or more mid-oceanic ridges. ...
due to the increase of anthropogenic
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
es and sulfate aerosols in the atmosphere also pose a long-term threat to the stability of various salt marsh habitats across the coastal US.  


See also

*
Anoxic waters Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. Anox ...
*
Firedamp Firedamp is any flammable gas found in coal mines, typically coalbed methane. It is particularly found in areas where the coal is bituminous. The gas accumulates in pockets in the coal and adjacent strata and when they are penetrated the releas ...
, produced naturally in
coal mines Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...
*
Hydric soil Hydric soil is soil which is permanently or seasonally saturated by water, resulting in anaerobic conditions, as found in wetlands. Overview Most soils are aerobic. This is important because plant roots respire (that is, they consume oxygen and ...
*
Landfill gas Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, ...
, produced incidentally where
municipal solid waste Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste, ...
is abandoned. *
Natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
*
Sewer gas Sewer gas is a complex, generally obnoxious smelling mixture of toxic and nontoxic gases produced and collected in sewage systems by the decomposition of organic household or industrial wastes, typical components of sewage. Sewer gases may inclu ...
*
Wetland methane emissions Greenhouse gas emissions from wetlands of concern consist primarily of methane and nitrous oxide emissions. Wetlands are the Methane emissions, largest natural source of atmospheric methane in the world, and therefore remain a major area of concern ...
*
Will-o'-the-wisp In folklore, a will-o'-the-wisp, will-o'-wisp or ''ignis fatuus'' (, plural ''ignes fatui''), is an atmospheric ghost light seen by travellers at night, especially over bogs, swamps or marshes. The phenomenon is known in English folk belief, ...
, mysterious lights that may be ignited by methane


References

{{Authority control Anaerobic digestion Biodegradation Gases Soil mechanics Methane Wetlands