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Title: Evolução dos aportes de metais pesados na Lagoa Rodrigues de Freitas, RJ
Other Titles: Heavy metals inputs evolutions in Rodrigo de Freitas Lagoon (RJ)
Keywords: Análise de fluxo;  Poluição;  Sedimento;  Metais pesados;  Lagoa Rodrigues de Freitas (RJ);  Flux analise;  Pollution;  Sediment;  Heavy metal;  Rodrigo de Freitas Lagoon (RJ)
Issue Date: 21-Feb-2006
Abstract: This work discusses the temporal variation of the heavy metals concentrations in a hypertrophic coastal lagoon located in the south zone of Rio de Janeiro municipality. The Rodrigo de Freitas Lagoon watershed includes a highly urbanized area without industrial activities. The only connection with the sea is through a channel built in 1921 with of 835 meters in length and width varying of 10 to 18 meters. Six sediment cores were collected in the lagoon between May and July of 2003. The concentration of the heavy metals (Fe, Al, Mn, Hg, Zn, Pb, Cu, Cd, Cr e Ni) in the sediment was analysed. With the objective of better understanding the behaviour of the metals along the sedimentary column, other complementary parameters were analysed, such as: organic matter and fine fraction contents, concentration of carbon, nitrogen, phosphorous and sulphur in the sediment; and determination of the sedimentation rate through the method of the excess of 210Pb. The sedimentation rate in sediment core T7 was calculated as being of 0.75 cm.year-1, indicating that 60 cm layer was deposited from approximately 1923. Therefore, the alterations in the dynamics of the Lagoon caused by the construction of the channel and the antropic activities were clearly indicated in this work. The results showed significant changes in the perceptual fine fraction and the organic matter fraction content before and after the layer of opening of the channel. The results still showed a gradual increment in the concentration of carbon, phosphorus and sulphur particulated starting from the 60 cm horizon to the surface, indicating an increase in the contribution of these elements for the Lagoon. The analysis of the cores showed a strong alteration in the concentrations of Hg, Cu, Pb, Zn and Cd, from the layer of the opening of the channel, it was verified a decrease of the concentrations of Mn and Ni. These results may indicate a modification of the oxygenation conditions of the lagoon waters in that time. In the more recent sedimentary layers the influence of the urbanization process thought the input of certain metals was observed.
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