Perturbations spatio-temporelles anthropiques sur l'ecosysteme marseillais

A chronological analysis of the disturbances caused to a pelagical ecosystem by domestic and industrial outfalls discharged on the surface of the coastal waters is done. Chronological series of various sampled parameters give evidence two fundamental components, a daily one (the trend) and the other one characterized by a periodicity of about 6 h, both linked to the different phases of human activities. Cross spectral analysis applied to salinity and phytoplankton series has pointed out a 50 min delay in the answer of phytoplankton communities to the periodical salinity variations. The use of the spectral principal components analysis allowed a description of the "hydrological" structure of the studied pelagical environment associated with 3 different frequencies and, on the hand, to reveal the leading part played by mixing processes.