Geochemistry of river suspended sediments in tropical watersheds: anthropogenic and granite-gneiss sources, SE Brazil

Resumo

The Piabanha watershed (2 x 103 km2) is located in the mountainous region of Rio de Janeiro, Brazil and it is an affluent of the Paraiba do Sul River, the most important river from the Brazilian southeastern coast.The total suspended sediment (TSS)  mineralogical analyses were performed with XRD. Geochemical analysis was done with EDXRF for SiO2, TiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, P2O5, SO3, BaO, ZnO, CuO, ZrO 2, SrO, Y2O3, Ga2O3, As2O3, Nb2O5, Rb2O, Cr2O3, SnO2 and Br. Quartz, kaolinite and gibbsite were the dominant in the TSS mineralogy, followed by feldspar and mica.The TSS geogenic source contrasted with pollution source from sewage. Granite and gneiss rocks contribution in the TSS of Piabanha watershed show a commonmineralogical and geochemical source. But the alluvial deposits from river banks might have been responsible for the differences between summer and winter samples.The major features in TSS from geogenic sources were SiO2, Al2O3, MgO, Ga2O3, Nb2O5, Rb2O, K2O, SrO, ZrO2 and TiO2. They showed a good correlation on the Si:Al molar ratio, and suggested that the source area is intensely weathered. Pollution features were given by significant TSS concentration of Fe2O3, MnO, ZnO, CuO, As2O3, CaO, Na2O, P2O5 and SO3 associated to sewage source.