Hydrogeochemical evaluation of thermal, mineral and cold waters between Bursa city and Mount Uludağ in the South Marmara region of Turkey

Abstract

The province of Bursa is located at the juxtaposition of the West Anatolian extensional zone and the middle and southern branches of the North Anatolian Fault in Turkey. Mount Uludağ, which has the highest elevation in Western Anatolia, is also located in the region. The Uludağ Massif, whose age is Oligocene, is a leucogranite pluton where numerous thermal, mineral and cold spring water discharges have been observed. These waters are extensively investigated for the first time in this study. Thermal waters discharge in the center of the city of Bursa, north of the Uludağ Pluton, and are utilized for balneology and spa purposes in hotels, while mineral waters discharge along a narrow tectonic valley southwest of the Pluton. Mineral waters are bottled and marketed by a few companies in the region. Cold spring waters discharge at different altitudes from Uludağ to the Bursa Plain. Temperatures of thermal waters vary between 37 and 80°C in the area of study. Thermal spring waters have been observed of two different compositions due to varying aquifer types: the Çekirge region thermal waters are characterized by Ca–HCO3 type water, while the Kükürtlü region thermal waters, are represented by Na–HCO3 type water, and have the highest temperatures due to deeper zone interaction in the reservoir. Both mineral and cold spring waters are characterized by Ca–HCO3 type water. In the study area, electrical conductivity values vary from 556 to 1352μS/cm in thermal waters, while cold water values change between 37 and 472μS/cm, and mineral and brackish waters values vary from 1402 to 4500μS/cm. Investigation of water–rock interaction effects shows different values for thermal and mineral waters. The δ18O values of thermal waters in the region are between −10.09 and −10.87‰, whereas the δ18O values of mineral waters are between −7.14 and −8.81‰. Isotopic signatures of all springs suggest a local meteoric origin of the feed waters from higher levels of the Uludağ Pluton. In the study area, the most effective water–rock interaction can be observed in mineral waters. An additional important process is cold water mixing; creating low thermal water temperatures in the study area. Thermal waters in the region show a close relationship with surface water and this effect can be clearly monitored by physical, chemical and isotope analyses during rainy seasons.