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

ABSTRACT

Mineralogy and geochemistry of the total suspended sediment (TSS) from a granite-gneiss watershed in southeast Brazil brought light to geogenic and anthropogenic sources. TSS was sampled in 15 points along the Piabanha watershed in summer (February 2013) and winter (August 2013). The Piabanha watershed (2 × 10³ km²) is located in the mountainous region of Rio de Janeiro, and it is an affluent of the Paraiba do Sul River, the most important river from the Brazilian southeastern coast. TSS mineralogical analyses were performed with X-ray powder diffraction. Geochemical analysis was done with energy dispersive X-ray fluorescence. Quartz, kaolinite and gibbsite were dominant in the TSS mineralogy, followed by feldspar and mica. Granite and gneiss rocks contribution in the TSS have a common mineralogical 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. The good correlation on the Si:Al molar ratio suggested that the source area is intensely weathered. Pollution features (sewage source) were given by significant TSS concentration of Fe₂O₃, MnO, ZnO, CuO, As₂O₃, CaO, Na₂O, P₂O₅ and SO₃.

KEYWORDS:

• Mineralogy
• total suspended sediment
• pollution

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCiD

Carla Semiramis Silveira http://orcid.org/0000-0002-1546-4719

Additional information

Funding

This research was supported by the Rio de Janeiro Research Foundation (FAPERJ) under [Grant E-26/111.387/2014], CNPq (Masters’ research fellowship) and CAPES (Proex).