Bacia hidrográfica do Rio Amazonas: contribuição para o enquadramento e preservação

Abstract

The present study was conducted in the Amazon River Basin, comprising the states of Amazonas, Roraima, Pará and Rondônia in order to rank the river water types by taking their natural characteristics into account. Two hundred eighty-nine (289), samples were collected from collecting stations placed along the Amazon River and its tributaries, based on class 2 of the CONAMA Resolution No. 357/2005, following the, high, and low water periods from March 2009 to July 2012. The techniques used were potentiometric condutometria, in visible spectrophotometry, mass spectrometry, inductively coupled plasma (ICP) and atomic absorption spectroscopy (A.A). The physical and chemical characteristics of the rivers are heterogeneous, with pH ranging from acid (3.6) to alkaline (7.56), dissolved oxygen from 1.41 mg/L (slightly oxygenated) to 10.00 mg/L (well oxygenated). In the rainy season the water is acidified, with more oxygen and higher levels of turbidity, suspended solids and silica. The waters of the Amazon River basin are bicarbonated and those of Andean origin (main channel of the Amazon River) are calcic. Data was grouped with the aid of descriptive statistics of R, and the natural water type boundaries were determined according to their regional standards. To assess whether there were differences in the types of water within the Amazon basin , we used cluster analysis (HCA), which showed the existence of three regions: a) the one further west that receives the influence of the Andean and pre-Andean rivers with higher electrical conductivity (40.00 to 80.00 μS/cm), pH ranging from slightly acidic to alkaline (values between 6.5 and 7.6) ex. the Amazon River and some tributaries of the right bank; b) the one to the north, influenced by the Guyana Shield, presenting slightly acidic water (pH between 4.6 and 6.5), and conductivity <40.00 μS/cm, such as. the tributaries of the left bank, and c ) a third region that is under the influence of the Brazilian Shield, the water going from slightly acidic to neutral ( pH between 6.0 and 7.0 ), also featuring low ionic charges with conductivity < 40.0 mS / cm, e.g., tributaries of the right bank of the lower Amazon, such as the Tapajós and Xingu. To estimate the natural limits of some variables considered to be critical, such as pH and dissolved oxygen (DO) , we used the median and quartiles ( percentiles, quartiles and deciles), obtaining the following results for each region: rivers of Andean or pre Andean origin presenting pH ranging from 6.03 to 7.23 OD and 2.12 to 6.04 mg / L, while the rivers originating from the Brazilian Shield the pH ranges from 6.16 to 6.94 OD 6.27 and 9.63 mg / L, and rivers that originate in Guyana Shield it showed to be between 4.66 and 6.66, while the outer diameter was between 2.05 and 7.79 mg/L. In addition to the above variables, we also have the natural color, which can reach 170.54 mgPt / L above legislation. Some metals also exceed the limits of Class 2, CONAMA Resolution No. 357/2005, namely: Ba (8.25 mg/L), Cd (0.87 mg/L), Zn (1.40 mg / L), Mn (1.045 mg/L), Al (0.18 mg / L) Ni (0.05 mg/L) Cr (0.17 mg/L) and Cu (0.14 mg/L). The Amazon presents its own regional peculiarities and our big challenge will be to classify, manage and preserve its natural resources along with both large and small watercourses. Considering the Amazon Basin large extent and number of its tributaries, the present study on sub-surface river waters, still shows to be insufficient for determining its regional standards.