Freshwater and Matter Inputs in the Aegean Coastal System

Largely using monitored data, we estimated water and nutrient fluxes to the Aegean Sea for two time periods, a past period (from 1980 to 1994 regarding discharge and 1980–1994 or broadly 1995–2000 regarding nutrients) and a recent period (between 2012 and 2015 for both, discharge and nutrients). The total water fluxes entering the Aegean were estimated to 481.4 km3/year, of which 62.3% were derived from the Black Sea via the Dardanelles straits, 26.8% by direct precipitation, 10.4% by the Balkan and Asian Minor rivers, and 2.2% by submarine springs. Regarding nutrients, considering only the Balkan rivers (in lack of data from Turkish rivers), the total fluxes of DIN (dissolved inorganic nitrogen) were 268.5 and of P-PO4 7.17 kt/year. The main DIN sources were the Black Sea inputs (48.4%) and precipitation (38.4%), whereas for phosphorus the rivers were the main contributors (46%). Considering this result, combined with the anticipated dramatic increase of hydropower production, there are concerns of enhanced future P limitation regarding marine photosynthesis as a result of more efficient phosphorus retention in reservoirs. Since silica is also massively retained within reservoirs, changes in riverine Si:N:P stoichiometry are expected to affect phytoplankton composition. Natural sediment fluxes were estimated to 61.8 Mt/year; however, sediment flux assessment includes large uncertainties. Retention of excessive sediment amounts within reservoirs, combined with a sea level rise, is expected to induce significant land losses in coastal areas. Finally, the Aegean Sea is still under threat regarding organic pollution, while there is a need for toxic pollutants monitoring and control in the circum-Aegean area to safeguard this spectacular environment for future generations.