Natural organic matter

Natural organic matter (NOM) is broken down organic matter that comes from plants and animals in the environment. NOM is a collective term, assigned to the realm of all of this broken down organic matter. Basic structures are created from cellulose, tannin, cutin, and lignin, 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 Earth.

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 molecule 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 ecosystem. After degrading and reacting, it can then move into soil and mainstream water 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 buffer, 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 rain.

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 matter and 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, groundwater) to move throughout the environment. This action of movement creates a cycle. Things decompose into NOM, travel through waterflow 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 Earth. 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 metal ions by binding to them. Once bound, the minerals and metal ions are less likely to move through the dirt when natural events like rain occur. Agriculture 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 dirt 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 biofouling, 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 chlorination, 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 journal showed proof that water with natural organic matter could be disinfected with ozone-initiated radical reactions. The ozone(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 electronegativity. 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 (entropy). 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.

Oxygen in Water Estimate on the Surface
We can essentially prove this by looking at this numerically. Remember that the surface of the Earth is 70% water. We can take the average Earth radius to be 6,367 meters. Using the surface area equation (SA=4(pi)(r^2)), we find that the surface area of Earth is roughly 5.094*10^8 meters squared. Than, multiply that number by 0.70 (percent of the earth that is water). This gives 3.566*10^8 meters squared of water. To include the volume element, multiply this number by the average depth of the ocean, which is 3,790 meters. This gives us an average volume of the water on the surface of 1.3515*10^12 meters cubed. We then need to convert this number to centimeters cubed because one centimeter cubed equals one mililiter. Multiply our number by 100^3 centimeters cubed, which equals 1^3 meter cubed. This gives us 1.3515*10^18 centimeters cubed, or 1.3515*10^18 mililiters. Then, we can use the density of water (roughly 1g/mL) to convert to grams, giving us 1.3515*10^18 grams of water. 18.02 grams of water is the mass for one mole of water. We divide our number by 18.02 grams per mole to give us the moles of water. The number now is 7.50*10^16 moles of water. Each mole of water has one mole of oxygen and two moles of hydrogen. So our number will stay the same as we multiply by one to convert it into moles of oxygen. That one mole of oxygen has 6.02x10^23 oxygen molecules. So we multiply our number by 6.02*10^23 molecules to get 4.517*10^40 oxygen molecules in the water on the surface of the planet. Please note this is an estimate taken from average data.

This is an astronomically huge number that nobody can even fathom. If you wanted to count to this number and you counted one number per second, it would take you 1.43*10^33 years to count to this number. In compasion, Earth has only been around for 4.55*10^9 years. This means that 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 crystallography. That method is standard to 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
 * 35-45% Oxygen
 * 3-5% Hydrogen
 * 1-4% Nitrogen

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 carbon 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.