Revista de Gestão Costeira Integrada
Volume 11, Número 2, Junho 2011, Páginas 207-217

DOI: 10.5894/rgci243
* Submissão: 18 Outubro 2010; Avaliação: 7 Novembro 2010; Recepção da versão revista: 11 Fevereiro 2011; Aceitação: 25 Fevereiro 2011; Disponibilização on-line: 1 Abril 2011

Environmental status of water and sediment around submarine outfalls – west coast of Portugal *

Qualidade da água e dos sedimentos na zona circundante de oito emissários submarinos – costa oeste de Portugal

Cristina Santos ^{@, 1}, Alexandra Barreiros ¹, Pilar Pestana ²,
Ana Cardoso ², Alexandre Freire ³

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@ - Autor correspondente / corresponding author: cristina.santos@lneg.pt
1 - Laboratório Nacional de Energia e Geologia. Estrada do Paço do Lumiar, nº 22, 1649-038 Lisboa, Portugal
2 - Instituto Hidrográfico. Rua das Trinas, nº 49, 1200-856 Lisboa, Portugal
3 - Inspecção-Geral do Ambiente e do Ordenamento do Território. Rua de “O Século”, 63, 1249-033 Lisboa, Portugal

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ABSTRACT
The sea along the western coast of Portugal presents hydrodynamic conditions that place it among the most favourable of European coastal waters for dilution and dispersion of waste water. Thus it is an appropriate zone for the location of submarine outfalls. According to the European Union Directives and Portuguese Regulations the waste waters produced by this densely populated coast should be treated, therefore 18 wastewater treatment plants with submarine outfalls were built along the coast.
Between 2002 and 2004, five sampling campaigns were performed in seven outfalls that were selected to participate in water and sediment quality surveys supported by INAG (Portuguese Water Institute), and performed by the Hydrographic Institute of the Portuguese Navy.
The water quality assessment was based on 10 chemical and physical parameters, including heavy metals. The results were compared with reference values and data from the largest flow outfall located at Guia, which has an autonomous monitoring program. In order to evaluate significant differences in water quality between years and sampling sites, statistical analyses were performed.
­­Sediments were evaluated for grain size, heavy metals, PAH, hydrocarbons, chlorinated pesticides and PCB. In order to evaluate the level of pollution of the different areas where the outfalls are located, the concentration factor (CF) (sediment/water elemental concentration ratio) was calculated and compared with the recommended values for the CF of each element.
The water sampling program did not allow identifying a clear seasonal evolutionary pattern. The environmental status of the waters surrounding the outfalls discharges comply, to a great extent, with the reference values proposed by INAG and did not revel high levels of contaminants. Due to the low sorptive capacity of the sediment for contaminants, trace metals, hydrocarbons and PAHs have a low environmental impact.
The values of the concentration factors for metals are below the recommended values.

Keywords: Portugal, submarine outfall, monitoring, receiving waters, sediments.

RESUMO
A costa oeste de Portugal apresenta condições hidrodinâmicas que a colocam entre as zonas mais favoráveis para a diluição e dispersão de águas residuais sendo, por isso, uma região adequada para a localização de emissários submarinos. Dos 18 emissários submarinos construídos ao longo da costa foram seleccionados sete da costa oeste. Cinco campanhas de recolha de amostras foram levadas a cabo entre 2002 e 2004 para participar em pesquisas de qualidade de água e de sedimento suportadas pelo INAG (Instituto da Água) e realizadas pelo Instituto Hidrográfico da Marinha Portuguesa. A avaliação da qualidade das águas baseou-se em parâmetros físicos e químicos, bem como metais pesados. Os resultados foram comparados com valores de referência e com os dados do emissário da Guia que tem um programa de monitorização autónomo. Os sedimentos foram avaliados para parâmetros químicos, metais pesados e granulometria. Para avaliar o nível de poluição das diferentes áreas, o factor de concentração (FC) foi calculado e comparado com os valores recomendados para o FC de cada elemento.

Palavras-chave: Portugal, emissário submarino, monitorização, meio receptor, sedimentos.

 

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