Data/hora: 01/06/2024 08:09:02

Provedor de dados: | 5
País: | France
Título: | L'utilisation de modèles écologiques dans la lutte contre l'eutrophisation des eaux côtières françaises
Autores: | Menesguen, Alain.
Data: | 1999-09
Ano: | 1999
Palavras-chave: | Ecological models; Hydrodynamical models; Residence time; Limiting factor; Phytoplankton blooms; Green tides; Coastal eutrophication; Modèles écologiques; Modèles hydrodynamiques; Temps de résidence; Elément limitant; Eau colorée; Marée verte; Eutrophisation côtière.
Resumo: | Increasing anthropogenic nitrogen and phosphorus loadings in some coastal areas have induced during the last twenty years excessive production of algal material, either phytoplanktonic or macrophytic. This so-called eutrophication phenomenon alters the usual structure of ecosystem and can lead to massive kills caused by anoxia in some extreme cases, when almost all the dissolved oxygen in bottom waters has been consumed by organic matter decomposition. Just behind the semi-enclosed lagoons, the most sensible areas are the dilution plumes of main rivers. In the case of French coasts, mediterranean lagoons have been eutrophicated for a long time, whereas the coastal areas of the Bay of Biscay and English Channel have been partially preserved by the strong tidal dispersion ; during the last two decades however, more and more spots of strong eutrophication did appear, caused by phytoplankton blooms (Bay of Seine, Bay of Vilaine and south Brittany) or Ulva mass blooms on beaches (several embayments on northern and western coasts of Brittany). Some questions arise:  1/ Which effects are to be expected from still increasing nitrogen loadings from agricultural sources ?  2/ To which level is it necessary to bring back these loadings if actions are impulsed to recover a good environmental quality in the eutrophicated sites ?  Only mathematical models are able to handle simultaneously the dynamics of all the main processes leading to eutrophication in the coastal zone : horizontal and vertical mixing by currents, erosion-deposition of particles, nutrient uptake by growing algae, remineralization of detrital organique matter...Picked up from recent studies done by the "Coastal Ecology" department at IFREMER/Brest, 3 different case studies are presented, in order to illustrate how ecological models can help understanding the shift in ecosystem structure, as well as building efficient scenarios for eutrophication control:  a/ the Bay of Lannion (western English Channel), which is an open embayment with strong tidal oscillation, but which is invaded every spring and summer by large Ulva accumulations ; public authorities have launched a recovery program, based on quantitative targets for loadings, computing by models.  b/ the eastern Bay of Seine (eastern English Channel), which is strongly enriched by loadings from the Seine river and exhibits frequent dinoflagellate blooms during summer, including some toxic species (Dinophysis sp.)  c/ the Bay of Brest, which can be considered as a naturally well-protected site, thanks to its strong tidal regime, but which is suspected to exhibit a slow increase of the summer dinoflagellate-dominated blooms due to constant lowering of Si/N ratios of marine waters in late spring and summer.
Tipo: | Text
Idioma: | Francês
Identificador: | http://archimer.ifremer.fr/doc/1999/rapport-144.pdf
Relação: | http://archimer.ifremer.fr/doc/00000/144/
Formato: | application/pdf