Water chemistry of rivers and streams from the Jau and Uatuma 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 Jau and Uatuma basins, Negro and Solimoes/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, NH4, Fe-dissolved, SiO2 and pH. This analysis showed the formation of five groups such as: 1) Solimoes-Amazon River; 2) Jau basin streams; 3) Padre stream; 4) Jau and Carabinani rivers (Jau basin); and 5) Uatuma basin streams, Uatuma and Abacate rivers, and Negro River. These waters showed typical Amazonian characteristics, with the exception of the Jau 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, NH4 and dissolved iron of the latter are unusually high if compared with other rivers and streams on the Uatuma basin. However, the K and silica concentrations were exceptionally lower than those of other Uatuma basin streams. The evaluated samples from the Jau and Uatuma basins could fit within the current classification as Intermediate Type A. Furthermore, the Jau 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.

Automated summary

This study investigates the concentration of dissolved ions and water chemistry patterns in rivers and streams of the Brazilian Amazon central part. The analysis reveals distinct groups based on the composition of dissolved ions, highlighting the atypical characteristics of the Jau River and the Padre stream. The findings contribute to understanding water chemical patterns and have implications for water resources management and conservation in the Amazon aquatic ecosystems.