The influence of an exceptional Po River flood on the physical and chemical oceanographic properties of the Adriatic Sea

Physical and chemical characteristics of the Adriatic Sea during 2001 are analyzed to better understand the influence of an exceptional flooding of the Po River (the largest river flowing into the Adriatic Sea) occurred in October 2000. Spatial and temporal distributions of water temperature, salinity, dissolved oxygen and nutrients over the basin are presented. To better understand the impact of river flood during 2001, an analysis of a data-set along a transect during the years 1999-2002 is carried out. Results confirmed that the Po River outflows strongly affect the physical and chemical characteristics of the basin. In particular, during 2001, a sharp decrease in salinity and an increase in nutrient and fluorescence concentrations occurred in the northwestern Adriatic Sea after the 2000 flood event. The amount of nutrients transported during the river flood into the northwestern part of the basin is depleted by phytoplankton uptake until April 2001. All the nutrients were consumed before they could enrich the eastern coast, even though the freshwater input extends towards the Croatian coast. The Po River discharge flowing into the North Adriatic Sea during October-November 2000 (about 5000 m3/s) is twice the mean discharge of the 2-month period (about 2000 m3/s) and diluting the basin sufficiently to influence the North Adriatic Deep Water formation, almost absent in winter 2001. The flood event contributed to modifying the physical and chemical dynamics of the Adriatic Sea and its influence is clearly visible even 5-6 months later.