Ismail Akcay , Suleyman Tugrul, Mustafa Yücel

The coastal ecosystem of the Northeastern (NE) Mediterranean has been affected by nutrient inputs originated from regional rivers and wastewater discharges leading to development of eutrophication. Atmospheric nutrient inputs have also remarkable contribution to marine nutrient pool in the NE Mediterranean, especially in dry periods. Sediment porewater nutrient fluxes into the deep waters are strongly associated with eutrophic and suboxic/anoxic conditions. There was only limited number of studies performed on the porewater and solid- state sediment biogeochemistry in the NE Mediterranean Sea having oxic conditions in the deep waters. In this study, therefore, sediment porewater (PW) nutrient (Si, N, P) and sediment organic matter biogeochemistry were studied. The study results indicated a series of redox reactions (oxic respiration, denitrification, iron reduction) as well as remarkable contribution of porewater diffusive nutrient fluxes to the total nutrient budget in the NE Mediterranean Sea. Lower Si/N and higher N/P molar ratios in the total nutrient inputs are very likely to modify phytoplankton composition and abundance in the phosphorus deficient NE Mediterranean productive shelf waters leading to development of mesotrophic/eutrophic conditions in the NE Mediterranean Sea.