Natural organic matter (NOM) is broken down organic matter that comes from plants and animals in the
environmentThe natural environment, commonly referred to simply as the environment, is a term that encompasses all living and non-living things occurring naturally on Earth or some region thereof....
. NOM is a collective term, assigned to the realm of all of this broken down organic matter. Basic structures are created from
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
,
tanninTannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit or red wine...
,
cutinCutin is one of two waxy polymers that are the main components of the plant cuticle which covers all aerial surfaces of plants. The other major cuticle polymer, which is much more readily preserved in the fossil record, is cutan...
, and
ligninLignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
, along with other various proteins, lipids, and sugars. NOM is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet. These two processes help to ensure the continuance of life on
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
.
How NOM is created
All living and growing matter on this planet contains organic components. Different types of matter include humans, animals, plants, and microorganisms. After the living matter dies, it decomposes. The organic matter from them and their excretions is broken down through an unknown reactive process into natural organic matter. Larger molecules of NOM can be formed from the polymerization of different parts of already broken down matter. The relative size, shape, and composition of a
moleculeA molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...
of NOM is very random. "NOM can vary greatly, depending on its origin, transformation mode, age, and existing environment, thus its bio-physico-chemical functions and properties vary with different environments."
Natural ecosystem functions
Natural organic matter is present throughout the
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
. After degrading and reacting, it can then move into
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
and mainstream
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
via waterflow. NOM forms molecules that contain nutrients as it passes through soil and water. It provides nutrition to living plant and animal species. NOM acts as a
bufferA buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of acid or base is added to it. Buffer solutions are used as a means...
, when in aqueous solution, to maintain a less acidic pH in the environment. Little is known why this occurs but research shows the buffer acting component to be crucial to wean away the effects of
acid rainAcid rain is rain or any other form of precipitation that is unusually acidic, i.e. elevated levels of hydrogen ions . It has harmful effects on plants, aquatic animals, and infrastructure. Acid rain is mostly caused by emissions of compounds of sulfur, nitrogen, and carbon which react with the...
.
Source cycle
A majority of NOM not already in the soil comes from groundwater, which is water under the surface of the earth. When the groundwater saturates the soil or sediment around it, NOM can freely move between the phases. But, the groundwater has its own sources of natural organic matter too:
- "organic matter deposits such as kerogen and coal
- soil and sediment organic matter
- organic matter infiltrating into the subsurface from rivers, lakes, and marine systems"
Note that one source of groundwater is
soil organic matterOrganic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds. The definition of organic matter varies upon the subject it is being used for....
and
sedimentary organic matterSedimentary organic matter includes the carbonaceous component of sediments and sedimentary rocks. The organic matter is usually a component of sedimentary material even if it is present in low abundance . Petroleum and natural gas are particular examples of sedimentary organic matter...
. The major method of movement into soil is from groundwater, but NOM from soil moves into groundwater as well. Most of the NOM in lakes, rivers, and surfaced water areas comes from deteriorated material in the water and surrounding shores. However, NOM can pass into or out of water to soil and sediment in the same respect as with the soil.
Importance of the cycle
Natural organic matter uses all these different phases (soil, sediment, water,and groundwater) to move throughout the environment. This action of movement creates a cycle. Things decompose into NOM, travel through water flow or soil, and then are free to spread through the phases. If it were not for this cycle, important nutrients such as minerals, vitamins, and metals would not be as easily spread throughout the surface of the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
. Furthermore, this shows there are no independent processes in the environment, which means everything is connected in some regard. Physical, biological, and chemical systems work together to create natural processes.
NOM in soil
Natural organic matter acts much like a fertilizer, but it does not provide the nutrients. It allows them to stay near the top of the soil. When in soil, the natural organic matter helps to enrich it with minerals and
metalA metal is a chemical element that is a good conductor of both electricity and heat, forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions...
ions by binding to them. Once bound, the minerals and metal ions are less likely to move through the soil when natural events like
rainRain is liquid precipitation, as opposed to other kinds of precipitation such as snow, hail and sleet. On Earth, it is the condensation of atmospheric water vapor into drops heavy enough to fall, often making it to the surface...
occur.
AgricultureAgriculture is the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of human civilization, with the husbandry of domesticated animals and plants creating food surpluses that enabled the development of more densely populated and...
is greatly affected, because NOM also improves structure and water retention for the soil. Then, the stationary material is more applicable to crops and plant life growing in the ground.
New compounds
There are also reactions that occur with NOM and other material in the soil to create compounds never seen before. Unfortunately, it is very difficult to characterize these because so little is known about natural organic matter in the first place. Research is currently being done to figure out more about these new compounds and how many of them are being formed.
Water purification
The same capability of natural organic matter that helped with water retention in soil creates problems for current water purification methods. In water, NOM can still bind to metal ions and minerals. These bound molecules are not necessarily stopped by the purification process, but do not cause harm to any humans, animals, or plants. However, because of the high level of reactivity of natural organic matter, byproducts that do not contain nutrients can be made. These byproducts are much larger and can induce
biofoulingBiofouling or biological fouling is the undesirable accumulation of microorganisms, plants, algae, and/or animals on wetted structures.-Impact:...
, which essentially breaks down water filtration systems in water purification facilities. The larger molecules clog the water purification filters intended to keep material like that out of drinking water. The fact that these byproducts are removed through purification is very good news, but having to replace filters constantly to maintain effectiveness is costly for water treatment businesses. This byproduct problem could be treated by the disinfection technique known as
chlorinationChlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
, which often breaks down residual material clogging systems, but research has shown that the natural organic matter also forms byproducts with this method.
Potential solutions
A large breakthrough could be underway after a paper published in the
Applied and Environmental Microbiology journalApplied and Environmental Microbiology is an academic journal published by the American Society for Microbiology. The title is commonly abbreviated AEM and the ISSN is 0099-2240 for the print version, and 1098-5336 for the electronic version....
showed proof that water with natural organic matter could be disinfected with ozone-initiated radical reactions. The
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
(three oxygens) has very strong oxidation characteristics. It can form hydroxyl radicals (OH) when it decomposes, which will react with the natural organic matter to shut down the problem of biofouling. The article did this on a very small scale of water and natural organic matter, so further research is being done to scale up the reaction. This journal article does show that solutions are on the horizon to prevent our water purification systems from being broken down by NOM.
False positives
Many water quality groups, such as the North Carolina State University Water Quality Group, believe that having too much natural organic material will cause deoxygenation and essentially remove oxygen from the water. Although organic material, which consists of many hydrocarbon and cyclic carbon chains, is susceptible to attack by oxygen, it would be sterically unfavorable to attach oxygens to every single carbon. Basically, molecules do not enjoy other molecules being too close to them when they have the same
electronegativityElectronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus...
. Most of this is because of electrostatic charge, which says that opposite charges are attracted and like charges are repelled. If you have oxygens (with a negative charge in theory) bonded to carbons next to each other, they will want to be as far away from each other as possible. Also, a larger molecule like oxygen (relative to carbon) does not want to attach to a carbon that already has oxygens on it when it could attach to a carbon without oxygens on it.
Of course, there are exceptions, such as varying the temperature at which these reactions occur. As the temperature becomes much higher, there is a better chance that an unfavorable reaction will occur because molecules move around faster increasing the randomness of the system (
entropyEntropy is a concept of information maintaining great importance in physics, chemistry, and information theory...
). Yet, as we consider the cold water in the natural environment, it is logical to see that all the oxygen in the water will not be consumed by NOM.
Estimate of oxygen in surface water
This can be proved numerically. The approximate volume of liquid water on the Earth is 1.333*10^9 km³, or 1.333*10^24 milliliters. Since the density of water is roughly 1g/mL, this is 1.333*10^24 grams of water. Dividing this number by 18.02 grams per mole gives 7.399*10^22 moles of water. Each mole of water has one
moleThe mole is a unit of amount of substance: it is an SI base unit, and one of the few units used to measure this physical quantity. The name "mole" was coined in German by Wilhelm Ostwald in 1893, although the related concept of equivalent mass had been in use at least a century earlier...
of oxygen and each mole of oxygen has 6.022x10^23 oxygen molecules. Multiplying 7.399*10^22 moles by 6.022*10^23 molecules/mole gives 4.456*10^46 oxygen molecules in the liquid water on the surface of the planet. (Please note this is an estimate taken from average data.)
NOM is not going to use up all the oxygen on the earth and remove water.
Chemical composition
Very little is currently known about natural organic material. Scientists are unable to crystallize it. This is important because once you can crystallize the material, it can be isolated and studied with
x-ray crystallographyX-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture...
. This method is standard for determining unknown compounds. NOM has not been characterized either and no unique structure is known. The best way to characterize NOM is by discovering chemical, physical, and thermodynamic properties of the matter. Analytical techniques are currently being discovered to allow this to happen. The only information scientists have is that NOM is heterogeneous and very complex. Generally, NOM, in terms of weight, is:
- 45-55% Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
- 35-45% Oxygen
Oxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
- 3-5% Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
- 1-4% Nitrogen
Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
The molecular weights of these compounds can vary drastically, depending on if they repolymerize or not, from 200-20,000 amu(4). It is also important to know that 10-35% of the
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
present forms aromatic rings. These rings are very stable due to resonance stabilization, so they are difficult to break down. The aromatic rings are also susceptible to electrophilic and nucleophilic attack from other electron-donating or electron-accepting material, which explains the possible polymerization to create larger molecules of NOM.
See also
- Biomass (ecology)
Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...
- International Humic Substances Society
The International Humic Substances Society is a scientific society that seeks to advance knowledge and research of natural organic matter in soil and water...
- Organic Chemistry
Organic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
- Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
- Sedimentary organic matter
Sedimentary organic matter includes the carbonaceous component of sediments and sedimentary rocks. The organic matter is usually a component of sedimentary material even if it is present in low abundance . Petroleum and natural gas are particular examples of sedimentary organic matter...
- Soil organic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds. The definition of organic matter varies upon the subject it is being used for....
External links