Chemical characterization and relevant geochemical aspects of suspended organic matter on the Amazon river delta

• Main Authors: Maamar El-Robrini, Waterloo Napoleão de Lima, Simone Baía Pereira
• Format: Article
• Language: English
• Published: Museu Paraense Emílio Goeldi 2006-04-01
• Series: Boletim do Museu Paraense Emílio Goeldi. Ciências Naturais
• Subjects: Geochemistry; Sediments; Organic matter; Humic material; Mouth of the Amazon river
• Online Access: http://www.museu-goeldi.br/editora/bn/artigos/cnv1n1_2006/caracterizacao%28pereira%29.pdf

Characteristics of geoenvironment of the Amazon river have been described by several researchers, where the appreciable extension of its drainage basin, the influence of the forest, erosion, seasonality, the considerable pluviometric index, the material transported in suspension and the notable discharge flown by the Atlantic ocean have been emphasized. This study, accomplished in Alive Resources of the exclusive Economic Zone Program (REVIZEE) ambit, in sediments samples collected in coastal waters of the Atlantic ocean under influence of the Amazon river, during the 2nd scientific cruise of the North Operation II, on ship-board Antares oceanographic, proceeds chemical characterization and it discusses important geochemistry aspects of the organic matter from bottom sediments and in suspension in the mouth of the great river. It was observed that the high concentrations of the suspended matter (maxim in 2300 mg.L-1) are met in collection points close to the coast, tending to zero off shore. The variation of the content of the organic matter associated to that suspended matter is relatively restricted (minimal in 1,91% and maximum in 3,53%). The identification of the chemical nature of the organic matter indicates the occurrence of humic material, probably associated to the drainage of characteristic amazon soils, as the podzols and the latosols, material transported by Amazon River as far as coastal waters. The chemical characterization of the humic material identified groups methylene (directly related with aliphatic hydrocarbons), of groups C=O (of carboxylate and/or ketones) and of bands owed the associated clayminerals. The content of organic matter was always shown below 3,6%, exhibiting reason values C/N varying from 9,64 (suspended matter) to 68,3 (bottom sediments), in agreement with the largest or smaller influence of nitrogen organic compounds and/or largest or smaller period of maturation of the organic material. In samples presenting higher reasons C/N; an origin should be waited in that dominate products of the decomposition of cellulose and/or which are associated to a period of more recent maturation. The content of present phosphate in the sediment, varying from 0,06% to 0,78% (expressed in mg.L-1 of P), suggests marine influences of the ambient (perhaps involving contributions of P biogenic), through the resuspension of sediments, being common in estuarines environments.