Southern Portugal: the Tagus and Sado estuaries
Cabeçadas, G.; Brogueira, M.J.; Cabeçadas, L. (2000). Southern Portugal: the Tagus and Sado estuaries, in: Sheppard, C.R.C. (Ed.) Seas at the millennium: an environmental evaluation: 1. Regional chapters: Europe, The Americas and West Africa. pp. 151-165
In: Sheppard, C.R.C. (Ed.) (2000). Seas at the millennium: an environmental evaluation: 1. Regional chapters: Europe, The Americas and West Africa. Pergamon: Amsterdam. ISBN 0-08-043207-7. XXI, 934 pp., meer
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Documenttype: Revisie
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| Auteurs | | Top |
- Cabeçadas, G.
- Brogueira, M.J.
- Cabeçadas, L.
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| Abstract |
The coastal waters of southern Portugal, which include the Tagus and Sado estuaries, are influenced by submarine canyons, headlands and by intense discharges of freshwater (the annual average flow of the Tagus river is about 400 m³ s-1). The area is also affected by intense upwelling processes, and changes in the last 10-15 years in the upwelling pattern off Portugal are thought to be responsible for decreasing recruitment of sardine and horse-mackerel. Spatial phytoplankton variability seems to be controlled, to some extent, by the establishment of a frontal boundary separating the river plume from tidally mixed nearshore waters; the boundary apparently functions as a barrier between two different phytoplankton populations, Thalassiosira spp. and Detonula pumila. Considerable work has been done in the Tagus estuary whose environment has been well characterised, particularly its dynamics related to the river regime and tidal conditions. The latter variables control the turbidity of the estuary and the materials deposited in the inner and outer shelf. Information on the biota of the zone -plankton and marine biological resources including fish, chephalopeds and benthic species- as well as on contamination by bacterial and pollutants, is fairly extensive. The system has a high biodiversity and, in general, is in reasonably good condition. However, in the inner parts of the Tagus estuary there are potential problems with high levels of Hg, Pb, TBTs and some bacterial contamination. The area is under considerable human pressure, being one of the most populated and industrialized regions of Portugal, and thus it receives considerable urban and industrial wastes. In addition to this there is intense maritime traffic and significant tourism in the area, and recent enterprises such as the EXPO Exhibition, the construction of the new bridge and several marinas have each led to specific but usually relatively minor environmental impacts. Dredging in the Tagus and Sado estuaries takes place regularly, and in the Tagus the amount of material removed increased by a additional 2.5 million tons during the construction of the new bridge, but monitoring studies undertaken during these operations apparently revealed no significant effects. In general, contaminants in fish, molluscs and bivalves are below those allowed in organisms for human consumption. The relatively healthy conditions of these Portuguese coastal waters are a result partly of the hydrological and biological characteristics of the system, and also a consequence of recent installation of several waste treatment systems, removal of some industrial complexes from the area, creation of estuarine and marine protected areas and as well as being aided by implementation of environmental and nature conservation legislation. |
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