Assessment of the hydrogeochemical characteristics of groundwater in two aquifer systems in Çumra Plain, Central Anatolia

Located in a semi-arid climate, Çumra (Konya) plain is one of the most important agricultural regions in Turkey. Groundwater is the major source for agricultural, domestic, and other water-related activities due to the insufficiency of surface water. As groundwater is the only major source of water in this area, it is important to know the effects of geological formations and anthropogenic activities on groundwater chemistry. This study was carried out with the objective of identifying the hydrogeochemical characteristics and processes controlling the groundwater chemistry in Çumra Plain, Central Anatolia, Turkey. The study area is comprised of two main aquifers which are the semi-confined aquifer of the Neogene age and the unconfined aquifer of the Quaternary age. To identify the hydrogeochemical characteristics of groundwater in two aquifer systems and to understand the major factors and mechanisms controlling the groundwater chemistry, graphical plots, mineral saturations, and multivariate statistical analysis of chemical constituents in the groundwater were used. Study results show that groundwater is generally neutral to slightly alkaline in nature with a pH ranging from 6.67 to 8.10, and the dominance of ions is in the order of Ca²⁺ > Mg²⁺ > Na⁺ > K⁺ for the Neogene aquifer and HCO₃ ⁻ > SO₄ ²⁻ > Cl⁻ > NO₃ ⁻; Mg²⁺ > Ca²⁺ > Na⁺ > K⁺ and SO₄ ²⁻ > HCO₃ ⁻ > Cl⁻ > NO₃ ⁻ for the Quaternary aquifer. While the chemical composition of groundwater in the Neogene aquifer is mainly controlled by water–rock interaction including dissolution of carbonates and gypsum, calcite precipitation, and de-dolomitization, the main geochemical processes in the Quaternary aquifer are reverse ion exchange, evaporation, dissolution of carbonates, gypsum and soil salts, calcite precipitation, and silicate weathering. The mechanism controlling groundwater chemistry in the Neogene aquifer is actually regulated by the geogenic processes (water–rock interaction) rather than by anthropogenic activities. However, the mechanism controlling groundwater chemistry in the Quaternary aquifer is regulated by both geogenic processes and anthropogenic activities. In addition, anthropogenic nitrogen pollution in the study area is currently not serious, but evaporation and leaching of soil salts due to anthropogenic activities increase the concentrations of ions in the Quaternary aquifer.