Projected change in atmospheric nitrogen deposition to the Baltic Sea towards 2020

Abstract

The ecological status of the Baltic Sea has for many years been affected by the high input of both waterborne and airborne nutrients. The focus is here on the airborne input of nitrogen (N) and the projected changes in this input, assuming the new National Emission Ceilings directive (NEC-II), currently under negotiation in the EU, is fulfilled towards the year 2020. The Danish Eulerian Hemispheric Model (DEHM) has been used to estimate the development in N deposition based on present day meteorology combined with present day (2007) or future (2020) anthropogenic emissions. By using a so called tagging method in the DEHM model, the contribution from ship traffic and from each of the nine countries with coastlines to the Baltic Sea has been assessed. The annual deposition to the Baltic Sea is estimated to be 203 k tonnes N for the present day scenario (2007) and 165 k tonnes N in the 2020 scenario, giving a projected reduction of 38 k tonnes N in the annual load in 2020. This equals a decline in N deposition of 19 %. The results from 20 model runs using the tagging method show that of the total N deposition in 2007, 52 % came from emissions within the bordering countries. By 2020 this is projected to decrease to 48 %. For some countries the projected decrease in N deposition arising from the implementation of the NEC-II directive will be a considerable part of the reductions agreed on in the provisional reduction targets of the Baltic Sea Action Plan. This underlines the importance of including projections like the current in future updates of the Baltic Sea Action Plan.