Estudos geoquímicos e bioecológicos dos foraminíferos bentônicos da Ria de Aveiro, Portugal

Abstract

Ria de Aveiro is a coastal lagoon located in an area on the north-western coast of Portugal which is heavily impacted by human action. Despite the measures adopted, several industries in the region are still responsible for the discharge of effluents in the lagoon. In order to characterize the environmental quality of the sediment and its effects on the population of benthic foraminifera, the following analyzes were carried out: physical and chemical parameters, grain size, mineralogical (pyrite content), geochemical (Al concentrations, As, Cd, Cr, Cu, Pb, S and Zn) and biochemical: total organic carbon (TOC), carbohydrates (CHO), lipids (LIP), proteins (PTN) and total biopolymers (TBP), and ecotoxicological analyzes of shells at 53 sample stations. The pollution load index (PLI) was used to identify the areas which were most polluted by metals that are considered as toxic (As, Cd, Cr, Cu, Pb and Zn). The concentration of biopolymers resulted in the classification of Ria de Aveiro as being a meso-oligotrophic to an eutrophic environment. The concentrations of TOC, TBT, LIP, PTN and CHO, as well as the concentration of trace elements reached maximum levels in locations of low hydrodynamics and highly populated areas. Eutrophic areas located to the north of Canal de Ovar, Largo da Coroa (higher concentrations of Zn), Largo Laranjo (high concentrations of As), Cidade de Aveiro (higher values of Pb and Cu) and port areas (increase of Cu). The species of foraminifera which is dominant and constant in all studied locations were Ammonia tepida and Haynesina germanica. The results presented do not discriminate against groups based on the quality of organic matter (biopolymers), since these are mainly associated with the amount of TOC. However, in the more eutrophic sites, where the highest levels of toxic trace elements are recorded, the foraminifera associations are made, especially by opportunistic species such as A. tepida, Ammonia parkinsoniana and Cribroelphidium excavatum. These species appear to be tolerant of other environmental variables that cause stress, such as low oxygenation of sediment and significant variations in salinity. In the most affected areas, the density of foraminifera drops and there is a reduction in its diversity. For ecotoxicological analyzes, concentration of metals in the shell, the chosen species was A. tepida for its potential of biomonitoring. Analyses indicated accumulation of trace elements on their foreheads. Thus, it can be seen that the hydrodynamics associated with the type of food are the factors that promote bioaccumulation and the effect of biomagnification. The presence of anomalies on the foreheads was not always linked to metal pollution. This study also demonstrated that there is no direct proportion to concentration levels of heavy metals in sediments at the concentrations found in the shells of foraminifera. The analysis of concentration of heavy metals in the shells of foraminiferal assemblages showed to be useful in the characterization and environmental monitoring