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Title: Determinação da origem da matéria orgânica sedimentar através de marcadores moleculares lipídios (álcoois graxos e esteróis) no sistema lagunar de Mandaú - Manguaba, AL.
Keywords: Mundaú Manguaba;  Marcadores moleculares;  Álcoois lineares;  esteróis;  Mundaú Manguaba;  Molecular markers;  Fatty alcohol;  Sterol
Issue Date: 29-Apr-2008
Abstract: Mundaú- Manguaba is a tropical, shallow coastal lagoon system, located at Maceió, the capital of Alagoas, northeast Brazil. This ecosystem suffers anthropogenic impacts originating mainly from urbanization and occupation of its margins, the extensive sugar-cane monoculture and the dispoasal of sludge and industrial waste, which fertilize its waters. The aim of this study is to evaluates the origin and the behaviour of the sedimentary organic matter, and also its degree of faecal contamination. Organic molecular markers (fatty alcohols and sterols), together with physical and organic bulk parameters (grain size, organic matter, C, N, and others) were quantified on sediment samples of the Mundaú and Manguaba lagoons, its fluvial sources (Mundaú, Sumaúma and Paraíba do Meio Rivers), a soil sample and on the channels connecting to the sea. The distribution of those compounds showed that the sedimentary organic matter of the lagoons originates essentially from its phytoplankton primary production. Fluvial sources and river mouths are both influenced by terrigenous materials, with a mix of authoctonous and allochtonous organic compounds. The long chain fatty alcohols served as efficient tools to evaluate the terrestrial influence. In contrast, the sterols were more efficient to determine the amount of faecal contribution close to Maceió´s waste disposal, with coprostanol attaining 4,4 μg/g of dry weight. Moreover, stanol/sterol ratios evidenced the early diagenesis of organic materials, specially those of autochthonous origin. The channel system presented low organic matter contents devoid of significant concentrations of the molecular markers, due to stronger advective exchange within the channels, favouring the predominance of sandy materials, rather than fine grained sediments, the last generally are associated to organic matter.
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