Sedimentation from suspension and sediment accumulation rate in the River Vistula prodelta, Gulf of Gdańsk (Baltic Sea)*

The River Vistula is one of the largest suppliers of fresh water and terrigenous matter to the Baltic Sea. The impact of this river on the Baltic coastal system and the fate of the sediment delivered to the Gulf of Gdańsk are not well understood. Spatial transport patterns, as well as the settling, deposition and accumulation of the sediments were studied at the Vistula prodelta in different seasons from January 2012 to January 2013. The concentration of suspended matter in the water column was measured with optical methods, the sedimentation rate was determined with sediment traps, and the sediment accumulation rate was estimated using 210Pb dating. Our data shows that the annual supply of sediment to the sediment-water interface exceeds the annual rate of sediment accumulation in the outer Vistula prodelta by a factor of three. Sediment trapping during rough weather showed that significant sediment redeposition was taking place, even at depths of 55 m. The dynamic sedimentary processes occurring in the Vistula prodelta mean that that more than two-thirds of the sediment mass can be remobilized and then redeposited in deeper parts of the Gdańsk Basin.