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Investigation of the recharge and discharge mechanisms of a complex aquifer system by using environmental isotopes and noble gases

Arslan, Şebnem
This study aims to determine the recharge, discharge and the mixing mechanisms of a complex aquifer system located above the Kazan trona ore field using the environmental isotopes of deuterium, oxygen-18, carbon-13 and carbon-14, chlorofluorocarbons (CFC- 11, CFC-12 and CFC-113) and the noble gas isotopes (He, Ne, Ar, Kr and Xe). The groundwater system consists of three different aquifers: shallow, middle and deep. The Akpınar formation lying between deep and middle systems acts as an aquitard. Oxygen-18 and deuterium data showed an isotopic contrast between the shallow and deeper aquifer systems and even between the unconfined and confined parts of the middle and deep aquifers. The Noble gas temperatures indicated the average yearly air temperatures in shallow aquifer system whereas the recharge temperatures came out to be lower than todays in deep groundwater system. This finding is also supported by the dissolved inorganic carbon’s radiocarbon activities being close to the detection limits in the same system. These activities together with the stable isotope data revealed there might be evidence of recharge to the middle and deep aquifer systems under colder climate conditions during the late Pleistocene. CFC concentrations indicated modern recharge to the shallow aquifer system, whereas the concentrations were close to the detection limits therefore CFC’s were unable to date the middle and deep aquifer systems however proved the existence of modern recharge to this system. Mantle-He escape to shallow aquifer system is believed to be along a deep buried fault system located in downgradient areas.