polmarcom2.jpg (12647 octets) Pollution by the oil slicks

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THE MEMORY OF ERIKA

   The great oil slicks are spectacular and tragicevents, which mark out the history of the maritime transport of hydrocarbons. Several great catastrophes occurred: most significant was that of the head of the well under sailor of Ixtoc One, in the Gulf of Mexico where 600 000 tons of the crude oil flowed in the ocean between June 1979 and February 1980 (either three Amoco Cadiz!!), but there was also in 1967, Torrey Canyon; in 1978 Amoco Cadiz; in 1989,Exxon Valdez and of course Erika in December 1999. They strongly disturbed all fauna and the marine flora.

  We are going to describe the consequences generated by an oil slick and how is carried out the repopulation of the flora.

  Let us take example sadly celebrates of Torrey Canyon oil Libérien. It failed on March 18, 1967 at the beginning of morning on one of Seven Stones, where it poured its 118000 tons of the crude oil Koweïtien.   The tablecloth touched the coasts of Cornouailles and the coasts French in Coast of Armor and Nord Finistère.   The English researchers estimated at 100 000 tons of algae destroyed in a few weeks by the oil slick, Re-colonization was followed during ten years. Imbalances were observed and fluctuations of the populations during the repopulation of the zones " intertidal  ", thus there is a competition between the algae limestones lithothamniées and of small shellfish (chtamales) and of imbalances between the algae wrack and the animals which nourish themselves some. It is necessary to await ten years before finding a new balance.

  naufrage erika.jpg (23770 octets)

The same consequences were observed after the ship wreck of the giant tanker Amoco Cadiz on March 16, 1978 opposite the small port of Portsall, with less than two miles of the western northern coast of Finistère, where it poured there 223 000 tons of light oil and 4000 tons of heavy fuel in a dozen days.   The ecological consequences of this oil slick were catastrophic, a total evaluation of the mortality undergone by the marine species was tried: on a total surface of 220 000 hectares including/understanding 50% of rock substrate, the biomass destroyed by pollution would represent 260 000 tons of fresh weight.  

      In bay of Morlaix, one observed a reduction of 20% of the number of the species, of 80% of the density of the individuals, 40% of the total biomass. Following such a catastrophe, one observes three stages:

- a phase of destruction of the alive species  ;

- then a phase of stabilization of which the duration varies few months at more than one year  ;

- and finally a phase of recolonisation and reorganization of the settlement which extends over one period from 6 to 10 years.

        Under our latitudes, six to seven years are enough to make disappear almost completely the traces from an oil slick. But there are zones where the massive oil arrival in very protected mediums remains polluted later on. Thus 13 years after the failure of Amoco Cadiz, certain marshes and some mudholes had still not found their repopulation of before the catastrophe

  All the dramas which I have just described to you are " accidents ". But the greatest oil slick of all times is not due to an accident but has the human madness: THE WAR.   It occurred in the Persian Gulf Arabo-, in 1991, during the war of Koweït.   The table cloths, caused by the ship wreck of bombarded tankers or the voluntary opening of valves of large tanks (" tactic " developed by the Iraqi military persons in charge) reach several hundred kilometers length. It is estimated that the widespread quantities of hydrocarbons can reach 1 million tons is the equivalent of four times the quantity poured by Amoco Cadiz.   In this not very deep and closed sea which constitutes the Gulf, where water renews one self only every 2 centuries, one can be certain very a long time that the damage will be felt a long time.

ois03.jpg (25644 octets)

So dramatic that is to say the short-term consequences of a pollution by hydrocarbon, there are thus almost no long-term traces.   The study of repopulations made it possible to high light the importance of succession of the various phases allowing the return and there organization of the alive species and the return to a new balance ofthe touched ecosystems. One estimates at 100 000 tons of oil which forwards each day at broad Bretonnes coasts. The French government thus set up in 1978 after the drama of Amoco Cadiz a plan of monitoring " the plan POLMAR " which controls the roads of navigation particularly reinforced in Handle to fight against marine pollution and an experimentation and research, resource centre established in Brest on accidental pollution of water.





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