Investigation of over-exploited groundwater in Çumra Plain (Konya-Turkey) with environmental isotopes

Abstract

The groundwater in the Çumra plain, a semi-arid climate region, is intensively exploited for human needs due to especially agricultural and demographic development. In the study area, there are two main aquifers which are the semi-confined Neogene aquifer and the unconfined Quaternary aquifer. This paper presents isotopic characteristics of groundwater of the over-exploited two aquifer systems in the Çumra Plain of Konya. ?18O and ?D contents of the Neogene aquifer samples respectively range from -9.89‰ to -6.76‰ and -68.30‰ to -47.50‰ in dry season and range from -10.32‰ to -7.61‰ and -68.63‰ to -53.11‰ in wet season. ?18O and ?D contents of the Quaternary aquifer samples respectively range from -8.43‰ to -5.53‰ and -58.67‰ to -45.61‰ in dry season and range from - 8.77‰ to -5.89‰ and -60.18‰ to -46.45‰ in wet season. The ?18O and ?D contents of groundwater samples in two aquifers indicate a meteoric origin. The average lower Oxygen-18 values of the Neogene aquifer samples indicate recharge from higher elevations while more enriched Oxygen-18 values of the Quaternary aquifer samples show recharged from lower elevation. The groundwater of the Quaternary aquifer was more affected by the evaporation eventuated during or after recharge. Besides, positive correlation of ?18O with both Cl and total dissolved solids (TDS) in the Quaternary aquifer samples reveals that the evaporation caused salinity increases of the Quaternary aquifer samples. Tritium contents of the Neogene aquifer samples vary from 0.22 to 2.15TU in dry season and from 0.85 to 2.64TU in wet season, while tritium contents of the Quaternary aquifer samples vary from 1.18 to 4.37TU and from 1.52 to 5.48TU in dry and wet seasons, respectively. Accordingly, the samples of the Neogene aquifer reflect relatively higher residence time. Besides, the Neogene aquifer is under the influence of relatively recent precipitation, but recent precipitation has contributed more to the Quaternary aquifer.