Author(s):
Fonseca, Rita 
; Patinha, Carla ; Barriga, Fernando ; Morais, Manuela
Date: 2012
Persistent ID: http://hdl.handle.net/10174/7843
Origin: Repositório Científico da Universidade de Évora
Subject(s): aquatic systems management; metals speciation; reservoir sediments; water quality
Description
In tropical climates, the high rainfall and temperature, throughout the annual cycle, allow high
leaching rates of metallic elements from the basin upstream, which accumulate in the reservoirs.
However, the concentration of these elements in natural waters is usually lower than expected, due
to the ease of adsorption and co-precipitation in solid phases. We have studied two tropical dam
reservoirs in Brazil, Três Marias (Minas Gerais) and Tucuruí (Pará), with the aim of understanding the
correlation between physical–chemical parameters of the water column, chemical and mineralogical
characteristics of the accumulated material and the solubility, mobilization and precipitation of
metals in reservoirs. Metals speciation performed in selected samples determined that metallic
micronutrients are preferentially adsorbed or retained through precipitation/co-precipitation onto
fine-size charged crystalline/amorphous Fe-oxides. Under the prevailing reducing and low pH
conditions of the bottom reservoirs, some adsorbed metals (particularly Fe and Mn) are easily
released from their metal bearing-phases and mobilized to the aqueous phase of sediments, which
show high levels of soluble forms of these elements. However, the solubilization process and the
release to the water column are not very extensive, as abundances of metals such as Fe, Mn, Zn and
Cu in water are low, although increasing with depth
