Abstract
anthropic influence, and the effects of the contamination on benthic foraminifera. The initial approach for measuring pollution was done through the load pollution index (LPI), based on As, Cd, Cr, Cu, Ni, Pb and Zn concentrations, and determined by total digestion of the sediments (TDS). This information was complemented by conducting a metal fractionation technique (sequential chemical extraction - SCE) in some of the most contaminated samples in order to define the relevance of different metal bearingphases (exchangeable cations adsorbed by clay and co-precipitated with carbonates, absorbed by organic matter and retained in the mineralogical phase) and to evaluate the toxic heavy metal availability. Multivariable statistical analyses were carried out taking into consideration the geochemical results, as well as the biotic (percentage of species/groups of species; foraminifer abundance and diversity) and abiotic variables, such as sediment content in mud, total organic carbon (TOC) and Eh. SCE results show that most of the element concentration in the sediments is retained in the resistant mineralogical phase. However, the higher bioavailability of some toxic elements, such as As, Cd, Cu, Hg, Ni, Pb and Zn, found in Laranjo Bay, Aveiro City, Aveiro Harbours and Espinheiro Channel, have a generic negative impact on benthic foraminifera of the Aveiro lagoon. Differential sensitivity of benthic foraminifera to high concentrations of heavy metals may exist. Quinqueloculina seminulum, for instance, seems to be more tolerant to higher bioavailable concentrations of Pb and Cu than Ammonia tepida or Haynesina germanica. Both species were previously considered to be the most heavy metal-tolerant foraminifer species. This study confirmed the use of benthic foraminifera as an important tool for the evaluation of the environmental quality of an ecosystem and for monitoring and restoring it.
Highlights
In the past decades, the degradation of aquatic environments has become a topic of increasing concern among the public
Contrary to the opinion of Rao and Rao (1979), miliolids in Ria de Aveiro, represented mostly by Q. seminulum, may be more tolerant to higher bioavailable concentrations of Cu and Pb than A. tepida, H. germanica and Elphidium spp
Measurement of the sedimentary total concentrations of toxic elements is useful as a general index of contamination, but may provide inadequate or little information about their availability, mobility or toxicity for the living beings
Summary
The degradation of aquatic environments has become a topic of increasing concern among the public. The main vulnerable areas of the lagoon, from a water quality point of view, seem to be the far end of the main channels, where a low dissolved oxygen concentration is observed (Lopes et al, 2005) and where eutrophication can occur (Lopes and Silva, 2006). These areas are affected by chemical contaminants related to anthropic actions. In Estarreja Channel, for example, industrial and urban effluents have been discharged, for several years, by the industrial plant north of the village of Estarreja, the so-called ‘Complexo Químico de Estarreja’ (e.g., Pereira et al, 2009, 2006, 2005, 1998a, b, 1995; Válega et al, 2008; Coelho et al., 2006, 2005; Ramalhosa et al, 2006; Monterroso et al, 2003; Abreu et al, 2000)
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