This study aims to analyze the concentrations and variations of cations (Na+, Mg2+, K+, Ca2+)
and trace elements (Li+, Sr2+, Rb+, Ba2+, U) in the waters of the Amazon River, near the city of
Óbidos during the years of 2012 and 2013. The sampling points cover 69% of the entire basin,
around 4.67 million km2 upstream. In order to cover all the heterogeneity of the river and its
tributaries, the samples were collected in a transect of the river, in 3 different points and equally
spaced at a depth of 0.5 meters, monthly. Chemical analyzes of the samples were performed
using Plasma Source Mass Spectrometry (ICP-MS). The results showed that during the study
period there was an abundance of Ca2+ cation following an order of predominance
Ca2+>Na+>Mg2+>K+. All cation concentrations varied according to the flood pulse of the river,
presenting, for the most part, peaks of concentration in the flood periods and lower
concentrations for the river ebb period. The trace elements followed, for the most part, the
tendency of the cations, presenting their highest and lowest values in the transitory periods of
the river, between the flood and the dry season. Its order of predominance was for
Sr2+>Ba2+>Li+>Rb+>U. The phases of the hydrograph (Flood, Full, Ebb and Dry) showed
significant differences for the concentrations of the studied compounds showing that there are
intra-annual variation in element concentrations in the river, but the same result was not
significant for the variation between the years of study maintaining a stability of the interannual
concentration. Therefore, the seasonality present in the Amazon River alters the concentration
of compounds making it important to understand the dynamics of these ions and modeling the
flow of these elements to the river.
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