Ecological quality status of the NE sector of the Guanabara Bay (Brazil): A case of living benthic foraminiferal resilience
2020
Alves Martins, Maria Virgínia | Hohenegger, Johann | Martínez-Colón, Michael | Frontalini, Fabrizio | Bergamashi, Sérgio | Laut, Lazaro | Belart, Pierre | Mahiques, Michel | Pereira, Egberto | Rodrigues, Rene | Terroso, Denise | Miranda, Paulo | Geraldes, Mauro César | Villena, Hélio Heringer | Reis, Tadeu | Socorro, Orangel Antonio Aguilera | Sousa, Silvia Helena de Mello e | Yamashita, Cintia | Rocha, Fernando
The ecological quality status of the NE region of the Guanabara Bay (SE Brazil), one of the most important Brazilian embayments, is evaluated. For this purpose, sediment samples from in the inner of the Guanabara Bay (GB) were collected and analyzed (grain-size, mineralogy, geochemistry and living foraminifera). In this study, it is hypothesized that the potentially toxic elements (PTEs) concentrations, in solution and associated with organic matter (OMPTEs, potential nutrient source), may represent two potential pathways to impact benthic foraminifers. A multiproxy approach applied to complex statistical analyses and ecological indexes shows that the study area is, in general, eutrophic (with high organic matter and low oxygen content), polluted by PTEs and oil. As a consequence, foraminifera are not abundant and their assemblages are poorly diversified and dominated by some stress-tolerant species (i.e., Ammonia tepida, Quinqueloculina seminula, Cribroelphidium excavatum). The results allow us to identify a set of species sensitive to eutrophication and OMPTEs. Factors such as the increase of organic matter contents and OMPTEs and, in particular of Zn, Cd and Pb, the oxygen depletion and the presence of oil, altogether contribute to a marked reduction in the abundance and diversity of foraminifera. Ammonia-Elphidium Index and the Foram Stress Index confirm that the NE zone of GB is, in general, “heavily polluted”, with “poor ecological quality status” and experiences suboxic to anoxic conditions. In light of it, special attention from public authorities and policymakers is required in order to take immediate actions to enable its environmental recovery.
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