Akademik Veri Yönetim Sistemi
GEOTHERMICS, cilt.138, 2026 (SCI-Expanded, Scopus)
Distinction between the different groundwater flow systems in karstic regions consitutes one of the main objectives of hydrogeological investigations. This paper attempts to demonstrate the combined use of hydrogeology, hydrgeochemistry, and isotope techniques for determination different groundwater flow patterns prevailing in the Orhangazi karstic basin. The Orhangazi area, which developed in relation to the I(center dot)znik graben, is located in the southeastern part of the Armutlu Peninsula, within the borders of Bursa province. The study area coverd by carbonate rock masses of Paleozoic age, where the tectonics is the effective factor controlling karstification. The Nad & imath;r, Kaynarca, Il & imath;p & imath;nar, and Gedelek-P & imath;narbas & cedil;& imath; are important karstic cold water springs that supply water to the town of Orhangazi. The Keramet-Il & imath;ca thermal springs of Orhangazi, at the northern end of Lake Iznik, issues from the NW-SE trending fault systems. Hydrochemical studies were conducted by in situ measurments, sampling and analyses of water samples from five different cites. Evaluation of the available data indicates that three groundwater circulation exist in the basin, namely shallow, intermidiate and deep regional flows. The characteristic values of temperature, electrical conductivity, carbonate alkalinity and logPO2 of the karstic effluents fed by shallow groundwater circulation are 13 degrees C, 412 & micro;S/cm, 3.5 meq/L HCO3- and 10-2 atm, respectively. Higher values, such as 34 degrees C, 980 & micro;S/cm, 9.4 meq/L HCO3- and 10 -1 atm are observed in the springs fed by regional deep groundwater flow. The Tritium data indicate that the springs fed by deep regional groundwater have longer residencetime. Elevated concentrat & imath;ons of Ca2+, Mg2+, and HCO3- are present in all springs, indicating that the dissolution of calcite and dolomite constitues the main water-rock interaction processes. The low SO4 2- concentrations in Orhangazi karstic waters can most likely be attributed to bacterial reduction of SO4 2-in the aquifers. The thermal waters are heated at depth by geothermal gradient caused by the neotectonic activity in the deep and ascend to the surface through fractures and faults by convection. The delta 18O, delta 2H and tritium compositions show that the thermal waters are of meteoric origin. A geothermal reservoir having probable temperature of about 70 degrees is the source of thermal water. The conductive process along with the mixing of deep thermal waters with shallow groundwaters is the main cooling mechanism. A conceptual hydrothermal model of recharge, mixing, and discharge has been proposed for the formation of the waters in the study area