Processos dominantes quanto à salinização de reservatórios em período de estiagem prolongada: o caso do Banabuiú

Abstract

The climatic and lithological conditions of the semi-arid northeast of Brazil are responsible for the intermittence of the surface water bodies and to guarantee the water supply it is necessary to store water. In this context, salinization causes deterioration of the water quality in the reservoirs and harms several uses, mainly in the agriculture. The dynamics of salts is influenced by several factors. In order to analyze them, the aim was to associate the tools of hydrochemistry and the quality indexes of agriculture to designate the processes responsible for the changes. This study aimed to determine the dominant processes in the salinization of the large reservoir Banabuiú and the effects on water quality for agriculture during prolonged drought when evaluating the period from 2005 to 2018. For this, it used linear correlations, precipitation data, Ionic Ratios, Chloro-alkaline Indices, Gibbs Diagram, Langelier Saturation Index, Residual Sodium Carbonate, Sodium Adsorption Ratio, USSL Diagram, and Piper Diagram. During prolonged drought, the predominance of the cationic and anionic hierarchies, Na+ > Mg2+ > Ca2+ > K+ and HCO3- > Cl- > SO42- > CO32- > NO3- was observed. Accumulation of calcium, potassium and magnesium was observed. The dominant salinization mechanism identified was weathering with the concentrating effect of climatic factors. Other active secondary processes were verified: reverse ionic exchanges, influence of dolomitic terrains, among others. The waters of the reservoir do not present a risk of sodification, they presented predominantly average risk of salinization and reached a high risk of salinization. These results indicate the origin of the ions and the influence of the drought in the ionic composition of the Banabuiú reservoir.