Geoquímica da água preta de rios do município de Apuí, Amazonas

Abstract

The present study evaluated Geochemical aspects of the black waters in the municipally of Apuí, south-east Amazon, with the objective of verifying your chemism, the influence of the hydrological cycle and of the water from rain and subterranean in the chemical composition of the rivers. Ten monthly collections were made between April 2009 and January 2010. The rivers Aripuanã, Jatuarana, Juma, Acari, Camaiú and Sucunduri, two streams were sampled along the BR-230 and a spring. These drainages are grouped in two sub-basins, the Aripuanã and the Canumã-Sucunduri are inserted in the basin of the Madeira River. The results were grouped in four seasonal periods: rainy, transition to dry, dry and transition to rainy. The major ions were determined by ion chromatography, the trace element by ICP-MS and SiO2 by spectrophotometry. The pH, electric conductivity and turbidity were determined by electrochemical methods. The DQO was analyzed by redox titrimetry with KMnO4.The Waters studied can be classified as Silicate and Potassium in all drainages and there is a predominance of cations over anions. The SiO2 is the most abundant constituent during the year. K is the second and predominating in the rainy season, while Ca in the transition to rainy. Among the trace elements, the most concentrated are Fe e Al in the drainages, except in the rainy season, when Zn is the most concentrated. In the spring, NO3, Na e K predominate, but among the trace elements the most concentrated is the Al, followed by Fe, however, in the transition the dry season , Cu is the second more concentrated. In Cluster analysis are observed three large associations were identified: one controlled by electric conductivity, with the major ions; the second is regulated by pH and has as major ion HCO3 e NO3; the last one presents the trace elements Cu, Ni, Co, Pb e Zn. However, each period groups the elements in different ways the that reinforces the heterogeneity of the Chemistry of the water along the hydrological cycle. As for provenience of the elements, Cl, Al, Rb e Pb there is a strong influence of rock, Ca, Mg, SiO2, HCO3, Fe, Zn, Sr e Ba represent the contribution of vegetation and Na, SO4, Cu and Ni are related to rain. In the transition to dry predominates the formation of gibbsite and in the kaolinite dry season (except in the spring). In the local sampled there is affinity with silicate rock of the craton, but there is indicative of carbonate influence on Jatuarana and Sucunduri the that characterizes their affinity with white waters of the Solimões River.