Fatores naturais e antrópicos que interferem na qualidade da água do rio Tocantins, trecho Baião-Mocajuba (PA)

Abstract

The water quality in hydrographic basins can be understood through studies involving physicalchemical, chemical, and biological parameters, taking into account anthropic activities and associated natural processes. The aim of this study was to analyze the behavior of physicalchemical and chemical parameters in different seasonal periods in the hydrographic basin of the Tocantins River, Baião-Mocajuba stretch, to discuss water quality based on the interaction of anthropic factors and natural processes. For this purpose, secondary data were collected, and samples were taken at two points (P1 and P2) during distinct seasonal periods (less rainy and rainy) and at mid-tide cycle (13h). The results were discussed in light of the theory regarding natural and anthropic factors in processes that may interfere with riverine hydrochemistry and water quality. Parameters such as temperature, pH, electrical conductivity, dissolved oxygen, and total dissolved solids were measured in situ, and samples were collected for the determination of chemical parameters (Fe, Mn, Pb, Cu, Cd, Se, Al, As, Ba, B, Co, Cr, Mo, Ni, V, Zn, Sr, Ti, BOD, COD, Cl, F, NO3, NO2, SO4, PO4, total nitrogen, SiO2, NH3, Ca, Mg, Na, K, P, Dissolved Organic Carbon, alkalinity, hardness). The data were analyzed using descriptive statistics, analysis of variance, correlation, and principal component analysis. The results indicate that seasonality is a factor influencing water quality parameter values, except for SO4, H4SiO4, Ba, and Sr. On the other hand, tidal effects are crucial in altering water quality parameters, especially during the less rainy period, but these alterations do not exceed the limits established by CONAMA 357/2005. Principal component analysis identified that Ca, Mg, Ba, Sr, Mn, and hardness accounted for 44.6% of water quality parameters during the less rainy period, while during the rainy period, Mg, K, Ba, hardness, Sr, Ca, Mn, Na, dissolved oxygen, and Al accounted for 47.67%. It is concluded that the Tocantins River hydrographic sub-basin has been impacted anthropogenically due to the construction of the dam and agricultural activities. Future studies are suggested to measure the effects of these activities on the water quality of the Tocantins River.