Long-term reanalysis, future scenarios and impacts of nitrogen deposition on northern European ecosystems including the Baltic Sea and the Scandinavian Mountains

Abstract

This study illustrates how a temporally consistent deposition reanalysis can be used 1/ as input data to ecosystem impact assessments, 2/ to understand past trends, and 3/ for validation of decadal to century-scale model scenarios. We have constructed a multi-decadal (1983–2013) reanalysis of nitrogen deposition (N_DEP) to northern Europe, including the Baltic Sea and the Scandinavian Mountains, using a combination of observations and modelling. We expanded the period with an operational annual reanalysis applying chemistry transport modelling, resulting in a fused dataset using the MATCH Sweden system for the period 1983–2021, and compared this to multi-century model scenarios of nitrogen deposition.

Since the 1980s, N_DEP has decreased until early 2010s in northern Europe including the Baltic Sea (by 32 %) and the Scandinavian Mountains (by 19 %). Present N_DEP is on pair with the levels in the 1950s, after peaking in 1980–1990. We project continued decrease in oxidized N_DEP until 2050, but still exceeding the pre-industrial levels. We also project an increase in reduced N_DEP from present to mid-21st century, with stronger signal compared to previous estimates. This results in a weakening of the annual reduction of N_DEP, stabilizing to the levels of the 1940s to 1950s by mid-21st century, resulting in approximately twice as high N_DEP compared to pre-industrial times. The projected N_DEP decrease will likely not be sufficient to avoid future effects on sensitive ecosystems. Thus, there is a need for continued efforts to further decrease nitrogen emissions to the atmosphere for protection of terrestrial and aquatic environments, not the least as ecosystems are under additional pressure of climate change and intensive management. The N_DEP trends and levels in our model scenarios compare well to the reanalysis results (including fused observations).