Decomposition

The process is a part of the nutrient cycle and is essential for recycling the finite matter that occupies physical space in the biosphere.

These processes release compounds such as cadaverine and putrescine, that are the chief source of the unmistakably putrid odor of decaying animal tissue.

[2] Prime decomposers are bacteria or fungi, though larger scavengers also play an important role in decomposition if the body is accessible to insects, mites and other animals.

The most important arthropods that are involved in the process include carrion beetles, mites,[4][5] the flesh-flies (Sarcophagidae) and blow-flies (Calliphoridae), such as the green bottle flies seen in the summer.

In North America, the most important non-insect animals that are typically involved in the process include mammal and bird scavengers, such as coyotes, dogs, wolves, foxes, rats, crows and vultures.

Aquatic and marine environments have break-down agents that include bacteria, fish, crustaceans, fly larvae[7] and other carrion scavengers.

From the moment of death, the body begins cooling or warming to match the temperature of the ambient environment, during a stage called algor mortis.

Shortly after death, within three to six hours, the muscular tissues become rigid and incapable of relaxing, during a stage called rigor mortis.

[13] The small amount of oxygen remaining in the body is quickly depleted by cellular metabolism and aerobic microbes naturally present in respiratory and gastrointestinal tracts, creating an ideal environment for the proliferation of anaerobic organisms.

In this stage, anaerobic metabolism takes place, leading to the accumulation of gases, such as hydrogen sulfide, carbon dioxide, methane and nitrogen.

The accumulation of gases within the bodily cavity causes the distention of the abdomen and gives a cadaver its overall bloated appearance.

[16] As the pressure of the gases within the body increases, fluids are forced to escape from natural orifices, such as the nose, mouth and anus, and enter the surrounding environment.

[14] Ruptures in the skin allow oxygen to re-enter the body and provide more surface area for the development of fly larvae and the activity of aerobic microorganisms.

The resurgence of plant growth is a positive sign, but it may take several years for the ecosystem to fully recover and return to its pre-disturbance state.

A basic guide for the effect of environment on decomposition is given as Casper's Law (or Ratio): if all other factors are equal, then, when there is free access of air a body decomposes twice as fast as if immersed in water and eight times faster than if buried in the earth.

On the surface in tropical areas, invertebrates alone can easily reduce a fully fleshed corpse to clean bones in under two weeks.

[28] This is one reason given for the lack of human remains found in the wreckage of the Titanic, even in parts of the ship considered inaccessible to scavengers.

[31] In extremely dry or cold conditions, the normal process of decomposition is halted – by either lack of moisture or temperature controls on bacterial and enzymatic action – causing the body to be preserved as a mummy.

They lack the internal microbial flora that produces much of decomposition[33] and quite commonly mummify if kept in even moderately dry conditions.

This process of putrefaction has a bad odor accompanied by it due to the hydrogen sulfide and organic matter containing sulfur.

Even when a body is decomposed, embalming treatment can still be achieved (the arterial system decays more slowly) but would not restore a natural appearance without extensive reconstruction and cosmetic work, and is largely used to control the foul odors due to decomposition.

[50] Another early process is physical breakup or fragmentation of the plant material into smaller pieces, providing greater surface area for colonization and attack by decomposers.

[56] Because of this nutritional enrichment, the fauna of saproxylic insects may develop and, in turn, affect dead wood, contributing to decomposition and nutrient cycling in the forest floor.

[57] Lignin is one such remaining product of decomposing plants with a very complex chemical structure, causing the rate of microbial breakdown to slow.

[58] In most grassland ecosystems, natural damage from fire, detritivores that feed on decaying matter, termites, grazing mammals, and the physical movement of animals through the grass are the primary agents of breakdown and nutrient cycling, while bacteria and fungi play the main roles in further decomposition.

[62] Decomposition rates and speed may differ or vary due to abiotic factors such as moisture level, temperature, and soil type.

[63] The rate of decomposition is governed by three sets of factors: the physical environment (temperature, moisture and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself.

[64] Soils which are rich in clay minerals tend to have lower decomposition rates, and thus, higher levels of organic matter.

The more labile compounds decompose quickly, leaving an increasing proportion of recalcitrant material called humus.

Microbial cell walls also contain recalcitrant materials like chitin, and these also accumulate as the microbes die, further reducing the quality of older soil organic matter.