Mechanisms that control the water characteristics of reservoirs in the state of Sergipe, Northeast Brazil

Abstract

The Gibbs diagram was used to identify the processes that potentially control the water chemical characteristics of the main reservoirs in the state of Sergipe, in northeastern Brazil. The water in the Poxim reservoir, initially controlled by atmospheric precipitation, quickly evolved into an ionic composition dominated by Ca²⁺ and HCO₃^-, as a consequence of the predominance of water-rock interaction. Weathering is the main mechanism that controls the water chemistry of the Jacarecica I, Jacarecica II, Macela, Ribeira, and Jabiberi reservoirs, with Na⁺ and HCO₃^- ionic domains, and the Dionísio, Ribeirópolis, Amargosa, and Cumbe reservoirs, with ionic domains. Na⁺ and Cl^-. The current ionic composition of water in the Taboca, Coité, Algodoeiro, Três Barras, Glória, Carira, and Lagoa do Rancho reservoirs is the result of chemical variations caused by successive evaporation processes. With the increase of evaporation, the water was salinizing and progressively changing from Na⁺ >> Ca²⁺ > Mg²⁺ and Cl^- >> HCO₃^-> SO₄^2- in Taboca and Coité, to Na⁺ >> Mg²⁺ > Ca²⁺ and Cl^- >> HCO₃^- > SO₄^2- in Três Barras and Algodoeiro, finally reaching Na⁺ >>> Mg²⁺> Ca²⁺ and Cl^- >>> SO₄^2- > HCO₃^- in Glória, Carira, and Lagoa do Rancho, the most salinized reservoirs. In general, the chemical characteristics of the reservoir waters were controlled by natural processes, such as water-rock interaction and evaporation, except for the Glória, Carira and Lagoa do Rancho reservoirs, where the anthropogenic impact showed a very significant contribution.