Bioturbation

see also: Etymology of Bioturbation

The concept of bioturbation indicates the phenomenon of transfer of nutritive or chemical elements by living beings within a compartment of an ecosystem or between various compartments. The word describes also the phenomenon of active mixture of the water or soil horizons by the alive, animal species mainly.

Thus if one has in a Aquarium of the layers of grounds of color and different texture, and that one places there some Vers of ground, by maintaining a humidity optimal for the worms, after a few months the whole of the layers are mixed and the color is homogeneous.

In an aquarium where stable layers of temperature and salinity and different oxygenation, the introduction of Zooplancton microscopic or macroscopic homogenizes the layers very quickly (if the conditions of temperature and salinity allow the mobility of this zooplancton).

The bioturbation, associated with the phenomenon of Bioconcentration contributes to the generalized contamination of the Prédateur S located at the head of the trophic Réseau. The contamination to the poles of the Seal S and Polar bear S shows the effectiveness of the transfers of Pollution by water and the air, like by the animals. Sometimes not only of the distant systems and which seem isolated like the the Baltic or the polar zones are not saved, but quite to the contrary, they have reconcentrent a considerable share of the pollution emitted well far from them, and for 250 years. From there of the animals such as the Cachalot S can transport in their organization, in a few days or weeks of the significant amounts of contaminants thousands of away kilometers where they can for example die and be eaten by Poisson S of deep seas or birds marine, which in their turn will diffuse these contaminants in other parts of the world, via the human consumption if necessary.

Space-time scales

The cycle biogeologic of the elements on planet is not a passive and entropic system. It to some extent “ is actively controlled ” by the Alive one, with its profit. All the species, and more still some of them, certain guilds or associations of species contribute to the circulation of the chemical elements, of the matter, certain forms of stored energy and nutrients. The mobilization is done especially in the ground, the Sédiment S and water, but the transfers can also relate to the air compartment where the insects and the birds at every moment move thousands of tons of matter, sometimes on long distance at each season of migration.

The distance covered by an element, as its speed of transfer strongly vary according to the biogeographic context and the species in question.

Let us take as illustration the case of an element which could be a Nutriment or a Oligoélément (Phosphore, Soufre or Potassium for example), or a toxic metal element, a Radionucléide or a pollutant Organochloré.

- Bactérie S can concentrate it and move it very locally, on a generally micrometric scale.

- Protozoon S or small Invertébrés can move them at a larger distance, generally centimetric or metric.

- digger Mushroom S, or animals such as the ground worm, or the Lapin which digs its burrow can move this element horizontally or vertically, more quickly, either by the dispersion of the ground, or by introducing it and transporting it.

- Certain mammals (whales for example), the fish and migratory birds can transfer it, in a few days with planetary scales.

Thus in Bielorussia, of the Césium coming from the repercussions of Tchernobyl, which would have percolé to 20 cm of depth 20 years after the accident, can be concentrated and brought back surfaces some by a Champignon, eaten by a Limace, consumed by a bird which will be later a few days in Africa where it can be in its turn consumed by the Man or another animal, or to die. In all the cases the element in question will have been moved.

The bioturbation takes much importance when it is done starting from sites rich person in a rare element, or in pollutants and when it utilizes organizations filterers or concentrators, or species of the top of the Food chain, that are for example respectively the Coquillage S filterers or the mushrooms.

Ecological function

Without the bioturbation, many vital elements would end up disappearing in the oceanic funds. Thus the Plankton reconcentre it the Sulfur brought continents by the rains and returns it when he dies in the Atmosphère where the rains will bring it to the emerged grounds.

In the same way one showed as the Saumon S which formerly went up the rivers per tens of million to lay in their native brook before dying there were the most important source of certain vital trace elements (Potassium, Magnésium, Iode that they accumulated in their organization at the time of their growth at sea) for the river, but also for most of the catchment area, thanks to the bioturbation (for example, the Ours, the Lynx which ate salmons in quantity diffused these trace elements via their Excrément S, but also the Insecte S and others species exporting of the organic matter of the river.

Certain species of ground worms (endogés) diffuse materials horizontally, other species (ear-endogés) go up these elements on the surface or hide them, enriching and homogenizing in a continuous way the surface horizon. In moderated zone, the totality of the first twenty centimetres of the ground of a meadow spent several times by the digestive tract of the ground worms.

Recycling of the excrements and of nécromasse

Species such as the Dung-beetle S or the Nécrophage S play an important role for the recycling and the dispersion respectively of the nutrients contained in the Excrément S and of the Nécromasse.

Éco-landscape functions

The bioturbation is opposed to part of the effects of the erosion;

initially while contributing to the phenomenon of humification and stabilization of the grounds,
then because fauna via its food recovers organic matter in the hollows (anticline|anticlines) and in particular in the wetlands, to diffuse it (in the form of excrements and of nécromasse) in the environment.

The animals of any size which nourish themselves in water and the sediments, if they leave this medium and do not die there (ex Têtard which becomes frog or clamping plate, larva of Chironome which emerges) or if they are extracted from it by a predator (fish eaten by a Héron) contribute to slow down the filling of the ponds and the wetlands, in a considerable way. They are million tons which annually are thus exported wetlands. In the whole of the mediums, the trophic Chain (food) extracted and thus transports considerable quantities of organic matter, with a geomorphological impact not measured but some.

Internal bonds

ecology of the landscape

External bonds

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