Spreading of riverine nitrate

Most nutrients (nitrogen and phosphorus) enter the Baltic Sea as river loads. Once inside the Baltic Sea ecosystem, they are transported with the currents. However, when they are taken up by organisms, their spreading pathway can be modified by sinking/sedimentation. To understand how this transport in the food web alters the transport in space, we applied a nutrient-tagging technique to our existing ecosystem model. This allows us to track the nutrients entering from different rivers. The video shows how nitrate from the rivers Odra (red), Vistula (green) and Njemen (blue) spreads in the river plumes before it is taken up by phytoplankton. The highest concentrations can be found in the shallow, near-coastal regions. After the phytoplankton dies, detritus sedimentation leads to denitrification in the sediments, which quickly removes the nitrogen from the ecosystem. Only few riverine nitrate is mixed into the open basins.

The simulation was done using the Modular Ocean Model (MOM3) and the ecosystem model ERGOM. The utilized setup has a grid size of 3 n.m. and 77 vertical layers. Calculations were performed at the HLRN supercomputing center, the project (BEST) was funded by the German Research Foundation (DFG).