Author(s):
Nunes, Marcelo Lopes 
Date: 2007
Persistent ID: http://hdl.handle.net/10773/2747
Origin: RIA - Repositório Institucional da Universidade de Aveiro
Subject(s): Geociências; Qualidade do ambiente; Qualidade do ambiente; Diatomáceas; Sedimentos fluviais
Description
O estudo geoquímico e biológico realizado na bacia hidrográfica do rio Caima
permitiu a identificação e a avaliação dos impactos ambientais nesta bacia
hidrográfica com particular ênfase nas áreas envolventes de antigas áreas
mineiras. Nestas áreas foram detectadas concentrações elevadas em Pb, Zn,
Cd, Cu e Fe nos sedimentos de corrente e em Pb e Zn nas águas de superfície
(especialmente no período do Outono). Uma avaliação completa da qualidade
do meio aquático foi estabelecida a partir da associação de índices
geoquímicos (Índice de Contaminação-IC) com índices biológicos (Índice de
Poluossensibilidade Específica-IPS e o Índice Biológico Diatómico-IBD).
ABSTRACT: The main purpose of the geochemical and biological study was the
identification and assessment of the possible environmental impacts in the
hydrographical basin of Caima and Mau rivers, with special emphasis on the
areas surrounding old mines of Pb, Cd and Zn. Data from stream sediment
samples (minus 80 mesh fraction) were used to undertake a preliminary
delimitation of the extent of contamination from Coval da Mó, Palhal and Braçal
mines.
The chemical data, particularly Pb, Cd and Zn concentrations, reveal that
significant environmental contamination occurs in the vicinity of the abandoned
mines. The presence of tailing deposits is identified as the main source of Pb,
Cd and Zn in the area. Extremely high Pb (3303 mg kg-1) and Cd (18.5 mg kg-1)
concentrations were observed in stream sediments collected in the Corga do
Coval da Mó and Mau streams as a result of the surface runoff. A decreasing
metal gradient was observed from Corga do Coval da Mó stream down to the
Caima river.
In order to study the effects of anthropogenic contaminants and other
environmental variables on the taxonomic composition, structure and
morphological changes of benthic diatom communities within a former mining
area (Coval da Mó), 20 sites were selected in the Caima and Mau river basins.
At the mining area, in the Corga do Coval da Mó stream, diatoms were
extremely rare. Two km downstream low abundance and diversity of diatom
taxa indicated a stressed environment. There, especially, Fragilaria capucina
var. rumpens but also Fragilaria crotonensis and Achnanthidium minutissimum
showed abnormal valves which may be related to the high levels of metals in
this area. Six km downstream in Fílvida mainstream, an increase in species
richness and diversity was registered while the relative percentage of
teratologies was lower. Available data on water chemistry suggest that the
diatom community patterns are mostly justified by the metal contamination,
because nutrients and organic matter revealed low concentrations, and
acidification did not occur.
The levels obtained for heavy metal concentration in sediments (in particular
Pb, Zn, Cd, Cu and Fe) and those obtained for superficial waters (Pb and Zn
only in autumn), showed the existence of contamination in the surroundings of
industrial and abandoned mining areas. A more reliable interpretation of the
collected data and a more complete assessment of the water quality were
made possible by the association of geochemical indices (CI – Contamination
Index) and biological indices SPI - Specific Pollution Sensitivity and BDI –
Biological Diatom Index). Doutoramento em Geociências
Document Type
Doctoral Thesis
Language
Portuguese
Advisor(s)
Silva, Eduardo Anselmo Ferreira da; Almeida, Salomé Fernandes Pinheiro de
