The Puraquequara River and its right-bank's tributary, the Água Branca stream, are located in the outskirts of the Manaus urbanized area and their basin is still harbored by the primary rain forest cover. They exhibit 'terra firme' geologic, pedologic and climatological characteristics pertaining to the Amazonian region. Samples for this research were collected in November 1998 (dry season) and April 1999 (rainy season). Water temperature, pH, turbidity, conductivity, alkalinity, hardness, COD, Ca2+, Mg2+, Na+ e K+, SiO2, NO3-, NO2-, PO4(3-), SO4(2-), Cl-, NH4+ and Fe were analysed. The water is acid (3.8 to 4.1) turning into less acid in the dry season. The alkalinity and turbidity are higher in the dry season whereas conductivity, hardness and COD are higher in the rainy season. SiO2 and Cl- are the main anionic elements where the former's contribution is higher in the Puraquequara and lower in the Água Branca while the latter shows inverse contribution. Na+, Fe, and NH4+ are the main cations with their higher contribution in the dry season. NH4+ is the only cation that tends to increase its contribution downstream in the wet season. K+ contents is higher than that of Mg+ and Ca2+ yet Na+ is the highest. The higher than 0.2 mg/L and 0.5 mg/L amounts of NH4+ and NO3- respectively, are traces of water contamination. These characteristics define these waters as very diluted with anions predominating over cations and correlated to the black water of the region.
Natural waters; Amazonian river; black water; physical and chemical parameters
