Water Typology in the Amazon: Close Correlation with the Hydrogeochemistry of River Basins

Abstract

A study on the typology of Amazonian waters was developed in the North Geographic Region of Brazil, considering a set of historical data from 1995 to 2022. The objective was to discuss and point out which environmental parameters are considered preponderant within the classification criteria of Amazonian waters. Historical data on temperature, density, pH, conductivity, oxygen, transparency, light attenuation, turbidity, color, total and dissolved solids, hardness, alkalinity, CaCO3, BOD, COD, main cations and anions, iron, C, N and P fractions, silicate, trace elements (Al, Cu, Zn and Mn) and chlorophyll a were analyzed. The analysis comprised water samples from the National Hydrometeorological Network (Sub-Basins 10 to 19), with a total of 36 basins, including tributaries, lakes and adjacent streams. The historical series was statistically analyzed through the techniques of Cluster, Principal component analysis (PCA), Piper Diagram and image interpolation by the ordinary kriging method. The results indicated a strong seasonal trend, with an evident distinction between the flood and ebb periods. The typology of white, black and clear waters was also evidenced, this last group being an intermediate class to the others, due to the physical-chemical standards. The PCA highlighted the parameters conductivity, pH, calcium, bicarbonate and Dissolved inorganic carbon (DIC) (Factor 1), and turbidity and alkalinity (Factor 2) as preponderant in the water classification. The ionic balance demonstrated that the white waters stood out for the highest concentrations of calcium and magnesium. The results suggest a pattern of calcic waters oscillating towards sodic and carbonated waters, with a subgroup in the northern eastern region of seasonally sodic-chlorinated waters, due to the influence of ocean tides. Image interpolation suggested a predominance of white waters in the western southern zone (Western Amazon) and white waters transitioning to clear waters in the eastern zone (Eastern Amazon). The analysis also showed a predominant strip of black and clear waters in the northern zone, and a strip of white waters in the central Amazon.