Variação intra e interanual de cátions dissolvidos e elementos traço no canal princi pal do Rio Amazonas, Óbidos - Pará

Abstract

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.