Chemometrics of the Environment: Hydrochemical Characterization of Groundwater in Lioua Plain (North Africa) Using Time Series and Multivariate Statistical Analysis

This study aims to analyze the chemical composition of Lioua's groundwater in order to determine the geological processes influencing the composition and origin of its chemical elements. Therefore, chemometrics techniques, such as multivariate statistical analysis (MSA) and time series methods (TSM) are used. Indeed, MSA includes a component analysis (PCA) and a cluster analysis (CA), while autocorrelation analysis (AA), supplemented by a simple spectral density analysis (SDA), is used for the TMS. PCA displays three main factors explaining a total variance (TV) of 85.01 %. Factors 1, 2, and 3 are 68.72%, 11.96%, and 8.89 % of TV, respectively. In the CA, total dissolved solids (TDS) and electrical conductivity (EC) controlled three groups. The elements SO42-, K+, and Ca2+ are closely related to TDS, the elements Na+, Cl-, and Mg2+ are closely related to CE, while HCO3- and NO3- indicate the dissociation of other chemical elements. AA shows a linear interrelationship of EC, Mg2+, Na+, K+, Cl-, and SO42-. However, NO3- and HCO3- indicate uncorrelated characteristics with other parameters. For SDA, the correlograms of Mg2+, Na+, K+, Cl-, and SO42- have a similar trend with EC. Nonetheless, pH, Ca2+, HCO3- and NO3- exhibit multiple peaks related to the presence of several distinct cyclic mechanisms. Using these techniques, the authors were able to draw the following conclusion: the geochemical processes impacting the chemical composition are (i) dissolution of evaporated mineral deposits, (ii) water-rock interaction, and (iii) evaporation process. In addition, the groundwater exhibits two bipolar characteristics, one recorded with negative and positive charges on pH and Ca+ and another recorded only with negative charges on HCO3- and NO3-. On the other hand, SO42-, K+, Ca2+, and TDS are the major predominant elements in the groundwater's chemical composition. Chloride presence mainly increases the electrical conductivity of water. The lithological factor is dominant in the overall mineralization of the Plio Quaternary surface aquifer waters. The origins of HCO3- and NO3- are as follows: HCO3- has a carbonate origin, whereas NO3- has an anthropogenic origin. The salinity was affected by Mg2+, SO42-, Cl-, Na+, K+, and EC. Ca2+, HCO3-, and NO3- result from human activity such as the usage of fertilizers, the carbonate facies outcrops, and domestic sewage.