Water quality assessment and hydrogeochemistry of a sedimentary basin in a semi-arid area under increasing exploitation: Insights from multivariate statistical analyses, GIS, and modeling

Abstract

The Paleozoic to Cretaceous sedimentary multi-layered aquifer systems of the sag-Jatobá Basin in semi-arid northeastern Brazil have been studied for quality assessment and screening of the factors controlling the groundwater chemistry evolution. Groundwater samples at 151 sites, maximum depth of 730 m, coupled with hydrological data characterizing the hydro-geological units were used to perform ionic ratios, GIS maps, modeling, and multivariate statistical analyses. The integrated statistical, GIS, and graphical techniques have shown the presence of five groups (i.e., C1 to C5), which increase salinity along the flowpath. C1 to C3 are mainly related to preferential recharge areas under unconfined conditions. The majority of these samples are Na+–HCO3− to Na+–Cl−. C4 samples are more evolved Na+–Cl− to Na+–mixed water roughly following flow path, likely related to areas of an aquifer system under semi-confined conditions. C5 samples have the highest TDS values with a typical Na+–Cl− groundwater type which coupled with the identified lithology reveals a greater degree of confinement. Groundwater chemistry evolution is controlled by climatic, geogenic, hydrologic, and anthropogenic factors mainly governed by evapotranspiration with subsequent cyclic salts dissolution and rock weathering in conjunction with the ion exchange, mixing with saline water, and nitrate contamination. The physical-chemical parameters of ∼85% of groundwater samples are within the World Health Organization (WHO) guidelines for drinking purposes. Conversely, irrigation ion-based indices such as salinity, Kelley Ratio, and Permeability Index showed that most groundwater is not suitable for irrigation if left untreated. The hydrogeochemical investigation contributed to the characterization and understanding of the flow and long-term geochemical evolution of the complex multi-layered aquifer systems of the Jatobá Basin. In this research, some guidelines are being proposed to be followed that may lead to a saving in global water resources while maximizing food production in similar arid to semi-arid areas.