Anthropogenic nutrient enrichment is expected to be a significant component of the Cilician Basin nutrient budget. Quantifying submarine groundwater discharge (SGD) impacts in the basin is crucial for establishing an ecosystem-based management scheme for the region. Therefore, we aimed to quantify SGD into the basin for the first time using ²²⁸Ra mass-balance modeling approach. Two seasonal basin-scale research cruises and two seasonal expeditions were conducted in 2022. A Lagrangian particle tracking model was used to predict offshore exchange rates. Finally, we defined a box model of ²²⁸Ra budget.²²⁸Ra activities ranged between 40-174 dpm/m³ in the river and 43-257 dpm/m³ in the groundwater during the wet season. The average activities were 27.0 dpm/m³, 15.6 dpm/m³ and 7.6 dpm/m³ in the basin's surface, intermediate, and deep water, respectively. The preliminary results indicated that the annual SGD water flux might be at least equal to or even up to 44 factor larger than annual riverine fluxes into the basin. The large span in the estimations may be attributed to the lack of a saline end-member in our estimations. The groundwater ²²⁸Ra activities were lower than previously reported, which may be linked to karstic geology. A prior research from a nearby area with similar geology has shown that fresh SGD may account for 30% to 80% of total SGD.  Based on this range, SGD-associated TIN, PO4, and Si fluxes might account for at least 50%, 18% and 86% of riverine nutrient loads, respectively. We conclude that SGD might be a major component of the nutrient budget of the basin.

Primary Presenter: Burak Kuyumcu, Middle East Technical University (kuyumcu.h2o@gmail.com)

Authors:

Burak Kuyumcu, Institute of Marine Sciences, Middle East Technical University, 33731, Erdemli, Türkiye   (kuyumcu.h2o@gmail.com)

Ekin Akoglu, Institute of Marine Sciences, Middle East Technical University, 33731, Erdemli, Türkiye   (ekin@ims.metu.edu.tr)

Serhat Ertuğrul, Institute of Marine Sciences, Middle East Technical University, 33731, Erdemli, Türkiye   (serhatertugrul@gmail.com)

İdil Kaya, Institute of Marine Sciences, Middle East Technical University, 33731, Erdemli, Türkiye. Department of Physics, Middle East Technical University, Ankara, Türkiye   (ilgaz.kaya@metu.edu.tr)

Serdar Bayari, Department of Geological Engineering, Hacettepe University, Ankara, Türkiye  (serdar@hacettepe.edu.tr)

Süleyman Özmen, Nuclear Technology and Radiation Safety, Vocational School of Technical Sciences, Akdeniz University, Antalya, Türkiye. Turkish Accelerator and Radiation Laboratory  (fatihozmen275@gmail.com)

Kanchan Maiti, Department of Oceanography and Coastal Sciences, College of the Coast and Environment, Louisiana State University, Baton Rouge, LA 70803, USA  (kmaiti@lsu.edu)

Koray Özhan, Institute of Marine Sciences, Middle East Technical University, 33731, Erdemli, Türkiye  (koray@ims.metu.edu.tr)

Korhan Özkan, Institute of Marine Sciences, Middle East Technical University  (okorhan@metu.edu.tr)