Water chemistry of rivers and streams from the Jaú and Uatumã basins in central Brazilian Amazon

This work reports on the concentration of dissolved ions and identifies water chemistry patterns by the analysis of 79 water samples from rivers and streams in the Jaú and Uatumã basins, Negro and Solimões/Amazon rivers in the Brazilian Amazon central part. This dataset was analyzed by means of a principal component analysis (PCA) followed by a one-way analysis of similarities (ANOSIM) and a Neighbor Joining Cluster analysis of the samples, explaining 50.8% of the limnological data variation, which was strongly influenced by electrical conductivity, alkalinity, Fe total , P total , NH 4 , Fe dissolved , SiO 2 and pH. This analysis showed the formation of five groups such as: 1) Solimões-Amazon River; 2) Jaú basin streams; 3) Padre stream; 4) Jaú and Carabinani rivers (Jaú basin); and 5) Uatumã basin streams, Uatumã and Abacate rivers, and Negro River. These waters showed typical Amazonian characteristics, with the exception of the Jaú River and the Padre stream. The hydrochemical parameters of the former did not correspond to the typical values of Amazonian blackwater rivers. The mean concentrations of color, COD, chloride, NH 4 and dissolved iron of the latter are unusually high if compared with other rivers and streams on the Uatumã basin. However, the K and silica concentrations were exceptionally lower than those of other Uatumã basin streams. The evaluated samples from the Jaú and Uatumã basins could fit within the current classification as Intermediate Type A. Furthermore, the Jaú River, during low water period, could fit within the Intermediate Type B category according to its geochemical features. This chemical characterization is extremely important when it comes to water Brazilian legislation and its adjustments for inclusion of the Amazon region waters. Hence, this paper may contribute to understanding such water chemical patterns, and to water resources management and conservation of these Amazon aquatic ecosystems.