Impact des boues résiduaires d'assainessement sur le plateau continental de Barcelone

Special issue Proceedings of the International Colloquium on the environment of epicontinental seas, 20-22 March 1990, Lille.-- 8 pages, 5 figures, 2 tables[EN] Sewage sludge from the Barcelona-Besós wastewater treatment plant has been discharged to the middle continental shelf off Barcelona through a pipeline 4 km in length since 1979. Around the mouth of the pipeline a waste deposit has settIed in the transition area between the muddy prodeltaic sediment and the sandy relict sediment of the outer part of the shelf, covering an area of 1 km2 to a maximum thickness of about 2.5 m. The waste material is finer and has much higher concentrations of Pb, Cr, Cu, Cd and Ni than the natural sediments which have accumulated previously at this area. In the middle shelf the dynamic processes are less energetic than in the littoral area. Thus, part of the solid waste is deposited near the mouth of the pipeline and the resulting waste deposit is not significantly affected by the action of bottom currents. However, it is affected by human activities such as trawl fishing. A fraction of the particles discharged through the pipeline rises to the surface water and can generate a column of suspended waste rising from the mouth of the pipeline to the surface. These particles concentrate at the surface levels of the water column, forming a patch of several hundred square metres of very turbid water. Dispersion of the partic1es depends on hydrographic and dynamic processes. The concentration of Cr, Cu, Cd and Ni in the suspended waste is higher than that detected in the waste deposit and the Pb concentration in the suspended waste is slightly lower than in the surface of the waste deposit[FR] Depuis 1979, la boue résiduaire de la station d'épuration des caux usées de Barcelone-Besós est déchargée sur le plateau continental de Barcelone par un émissaire sous-marin de 4 km de longueur. Au débouché de l'émissaire s'est accumulé un dépôt dans la zone de transition entre les sédiments vaseux prodeltaïques et les sédiments sablonneux de la partie extérieure du plateau continental. [...