DiagnÃstico geoquÃmico e geocronologia do sistema estuarino-lagunar do roteiro Alagoas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The estuarine lagoon system of the Roteiro is located in the central coast of Alagoas, showing the largest continuous area of preserved mangroves of the State of Alagoas. This ecosystem has been heavily impacted by various anthropogenic activities such as urbanization, the cultivation of oysters, the gas production, the manufacture of cement and the cultivation of sugar cane. This work aimed to the diagnosis geochronology and geochemical Estuary Lagoon System of the Roteiro. Was examined the vertical distribution of concentration of some heavy metals (Fe, Mn, Al, Ni, Co, Cd, Pb and Cu) in testimony (up to 1 meter) of sediment dating background. The geochemical analysis of samples of bottom sediment is shown that the elements examined had concentrations characteristic of a non-polluted estuary (Fe: 3.736 to 11.197 mg.kg-1, Mn: 45 to 140 mg.kg-1, Al: 1.635 to 3.255 mg.kg-1, Ni: 3.3 to 8.5 mg.kg-1, Co: 1.02 to 3.3 mg.kg-1, Cd: 0.035 to 0.16 mg.kg-1, Pb : 0.18 to 7.78 mg.kg-1, Cu: 1.6 to 11 mg.kg-1). The enrichment factor, suggesting a lack of pollution were obtained for most elements analyzed with the exception of Fe. The iron had the highest concentration in the outfall system, which suggests pollution possibly correlated to a source close to geogenically system. The geochronological study was based on this determination of 210Pb in sediment samples. The concentrations of heavy metals were determined by the technique of atomic absorption spectrometry coupled with graphite furnace (GFAAS). Through the time the concentrations of the elements Ni-Co-Cu-Cd and Pb showed a decrease that of 30 years ago period that began the process of integration of environmental legislation to protect these environments. It also assessed the interference of the hydrodynamic characteristics of the system in the process of sedimentation in the coastal environment. The results of the geochronological study of the sediments showed a significant increase in the rate of sedimentation of the system. For the testimony 1, the sedimentation rate was 0.42 cm.ano-1, thus defining the 3-cm layer was deposited for about 13 years, the testemony 2 presented a rate of 0.82 cm.ano-1 in 1995, considered the highest among the three testimonies, which reflects a sedimentation accelerated. This point has intense sedimentation, possibly associated with anthropogenic sources geogenically and that may be associated with the cultivation of oysters that occurs at this point. The rate of sedimentation in evidence 3 was 0.35 cm.ano-1 to about 74 years ago. This increase may be linked to the period of occupation of the areas of Atlantic forest and replacing it by the sugar cane in the coastal tableland of the municipalities of Barra de SÃo Miguel and Roteiro (the surrounding area) between the 1970s and 1990s, encouraged by PROALCOOL. The geochemical analysis of concentrations of heavy metals in sediment samples showed that the environmental impacts caused by the system in the last 40 years are considered acceptable when compared with the standards of Canadian references (ISQG and PEL), American (ERM and ERL) and CONAMA

ASSUNTO(S)

estuary lagoon system of the roteiro taxa de sedimentaÃÃo e sistema estuarino lagunar do roteiro sedimentation rate geociÃncias geoquÃmica de metais pesados geologia geochemistry of heavy metals geocronologia 210pb 210pb geochronology

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