Contribution of anthropogenic inputs in the salinization process of the Dionísio Machado reservoir

Abstract

In this study, the evolution of water salinity in the Dionísio Machado reservoir, located in the city of Lagarto in the state of Sergipe, Brazil, was evaluated based on hydrochemical data and using multivariate statistical analysis. Ten samples of surface water were collected, in the dry and rainy periods from 2013 to 2019, and the following parameters were measured: pH, electrical conductivity (EC), total dissolved solids (TDS), Na⁺, K⁺, Ca^2+, Mg^2+, SO₄^2-, Cl ^- and HCO₃^-. The Principal Components Analysis separated the samples into three groups, depending on their mineral composition (ion concentrations, EC, TDS), with Group I being the samples with TDS < 500 mg L^-1; in Group II samples with TDS > 500 and < 600 mg L^-1 and in Group III samples with TDS >1000 mg L^-1. Water salinity, measured by TDS, varied from 300 mg L^-1 in 2013 to 1574 mg L^-1 in 2019. The Gibbs diagram indicated that evaporation is not the dominant process controlling the ionic composition of water, i.e., the salinity of the reservoir. The results showed that the increasing salinization process of the reservoir is controlled, mainly, by the impact of anthropogenic inputs associated with sewage effluents, urban drainage and industrial effluents.