Influence of Aveiro Lagoon heavy metal contents in the adjacent continental shelf (Portugal)

I Abrantes,Ja Dias,J Vidinha,F Rocha

doi:10.7773/cm.v31i12.99

I Abrantes, Ja Dias + Show 2 more

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https://doi.org/10.7773/cm.v31i12.99

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Abstract

A chemical analysis of Al, Ca, Fe, Mg, Cu, Pb, Zn, Cr, Co, Ni and Cd was carried out in 22 surface sediment samples of the continental shelf and upper slope between Espinho and Aveiro (Portugal). To reduce the disturbing effects of grain size, all samples were size-normalized by wet sieving (<63 µm). The fine fraction was digested with concentrated acids and analyzed by flame atomic absorption spectrometry. The Al and heavy metal concentrations displayed a similar distribution pattern, decreasing seaward. Exceptions to this general pattern are Ca, Mg and Pb distributions. The Ca contents are related to carbonated biogenic particles that are very abundant in the outer shelf. Multivariate statistical analysis was applied to all data to assess the behaviour and sources of each element analyzed. The results from factor analysis showed that terrigenous supply (from Aveiro Lagoon flow, coastal erosion and littoral drift), grain size (clay) sorting and anthropogenic influences from Aveiro Lagoon are the major factors controlling spatial variations of chemical elements in the continental shelf between Espinho and Aveiro. Unusually high contents of Pb were found in the middle shelf off Furadouro, but we could not determine the possible source of this contamination.

Highlights

This work aims to evaluate the distribution of several elements, in particular the heavy metals, in the fine fraction of the surface sediments and to correlate trace metal content with natural or anthropogenic inputs
The 22 shelf sediment samples analyzed were collected using a Smith-McIntyre grab, during several cruises conducted under the SEPLAT program, promoted by the Portuguese Hydrographic Institute, between 1988 and 1990
The chemical analysis of the sediment samples was carried out following the method proposed by Lecomte and Sondag (1980): 1 g of sediment was digested with a mixture of 3 mL of HCl (37%), 2 mL of HNO3 (65%) and 1 mL of HF (40%)

Summary

Introduction

IntroducciónSeveral studies regarding mineralogical distribution in the fine fractions of the sediments from the Portuguese Atlantic coast and continental platform in relation to circulation/ paleocirculation have been carried out during the last decade (Drago et al, 2002; Machado et al, 1999a, 1999b, 2000, 2001a, 2001b, 2002; Martins et al, 2001a, 2001b, 2002; Oliveira et al, 1998, 2000, 2001, 2002; Vidinha et al, 1998, 2000, 2002). The main topics were and still are: En la última década se han realizado varios trabajos sobre la distribución mineralógica en las fracciones finas de sedimentos de la costa Atlántica y plataforma continental de Portugal en relación con la circulación y paleocirculación (Drago et al, 2002; Machado et al, 1999a, 1999b, 2000, 2001a, 2001b, 2002; Martins et al, 2001a, 2001b, 2002; Oliveira et al, 1998, 2000, 2001, 2002; Vidinha et al, 1998, 2000, 2002). Estudios sobre la composición mineralógica de sedimentos del fondo del mar, de material particulado en suspensión y en núcleos, junto con datos paleontológicos y geoquímicos, para llevar a cabo reconstrucciones paleoclimáticas y paleoambientales, así como análisis de cambios en el nivel del mar, identificar las correlaciones estratigráficas, las fuentes de sedimentos en el pasado y actuales y de contribución terrígena, la dispersión de la contaminación y, finalmente, describir las masas de agua oceánica actuales

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