Dystrophisation

The dystrophisation is the extreme state of the Eutrophisation, which results in the death of the animal and vegetable organizations higher.

Process:

In the ponds and ponds:

the Bacterium S Aerobic S and the Algue S pullulate following an excessive biodegradable organic matter contribution, itself generated by an excess of nutrient. The algae accumulate naturally surfaces some where the sunning is most important.
the bacteria (and the zooplancton made up of the animal organizations which in the first time eat them) impoverishment quickly medium out of oxygen dissolved (vases, water), in particular the night when photosynthesis is inactive and that the plants and the other organizations consume dissolved oxygen and expire of CO2.
the rise of the rate of CO2 and nutrients causes a development even more significant of phytoplankton and/or algae of surface, which will make obstacle with the penetration of the sun and UV in water.
the aerobic organizations die in the deepest layers, while releasing from CO2, the CH4, the nitrogen and the phosphorus which still will enrich the medium and will accelerate the process which then will be autoentretenir (part of nitrogen evaporates, but the phospore remains mobilizable in water and maintains the dystrophisation).
the Zooplancton, the organizations mobile (Poisson S, Amphibian S, Invertebrate S) having disappeared, whereas the capacity of the wind to oxygenate and brew the layers of water also decreases, and a hot layer being formed on the surface, the deep water D-are not oxygenated any more (thermocline effect + reduced mixing of water).
After a certain time, only the anaerobic bacteria survive in a black and putrid mud. Fermentation that they maintain there releases from gases such as the hydrogen sulfide, ammonia and methane, unfavourable with higher forms of life.

The contributions of nutrients agricultural or resulting from the increased erosion of the grounds are often clearly in question; but locally, the old immersion of waste, soldiers in particular (immersed Ammunition, explosives containing nitrates) could also be in question or worsen the phenomenon, at sea Baltique in particular, but also on the western frontage of Europe (see central chart of report/ratio OSPAR.

Solutions

To limit or fight the dystrophisation, it is necessary:

to stop the source of nutrients eutrophisants;
to export the plants which pullulate on the surface, by taking care that, by scrubbing, the nutrients which they contain do not return in water.

Mechanical oxygenation or by Bulleur of the medium can accelerate the process of purification, also contributing to the mixture of the layers. the export of the vases can also belong to the process, but it is more expensive.

In the estuaries

the phenomenon can exist in the middle of certain Estuaire S, in the muddy Bouchon which is often touched by eutrophication, which to a certain extent and at certain times is natural. It is for example the case following the river contributions with the autumn or after violent rains with floods. But the proofing and agriculture exacerbated these phenomena.
the phenomenon also exists in different forms in the closed seas and bays where water is renewed little, where occur then planktonique blooms accompanied by conditions of Anoxie. The risk is highest in the zones where the agricultural contributions of nutrients starting from the estuaries or the rains (nitrogenizes dissolved) are excessive.

Dans the extreme cases are formed dead zones being able to reach tens of square kilometers, even much more. UNO identified in the world a hundred of these “Dead Zones” where vast surfaces are sometimes concerned (approximately 22.000 km2 for vastest in 2007). The pullulation of certain primitive species of bacteria or producing plankton of toxins can also exacerbate phenomena of mortality which still worsen the effects of the anoxia.

See too

planktonique Eutrophication
Bloom
dead Zone
Nitrate, Phosphate
Erosion

External bonds

X-ray EHP one line

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