Net anthropogenic N and P inputs (NANI/NAPI) to the Baltic Sea drainage basin peaked in the 1970s and 1980s and have since then stabilized on lower levels. Of the cumulative 1900 – 2018 inputs, only 15% of NANI and 6% of NAPI have left the drainage basin as waterborne loads to the Baltic Sea. To clarify the fate of the remaining inputs, we have constructed a dynamic model that routes NANI and NAPI either via rapid transfer or through mobile terrestrial and aquatic storage pools into the Baltic Sea, with losses to terrestrial and aquatic sinks in proportion to the storage pools. We have disaggregated the Baltic Sea catchment into seven regions and calibrated our model to reproduce riverine loads of N and P in each subregion. Fluxes from the mobile terrestrial storage pool dominated anthropogenic riverine N and P loads in the southern part of Baltic Sea, whereas rapid transfers were equally important in the northern boreal basins. In total, 67% of the 1900 – 2018 NANI inputs and 82% of NAPI were lost to terrestrial and aquatic sinks, and only 12% of both NANI and NAPI were still retained in mobile pools in 2018. Residence times in the mobile storage pools were 5 – 7 years for N and 10 – 22 years for P in the southern part of the Baltic Sea; but longer in the boreal basins with larger rapid losses. In 2018, mobile storage pools were close to steady-state given present inputs, but mobile P pools would continue their decline and cause a further decrease in riverine P loads.

Primary Presenter: Bärbel Müller-Karulis, Stockholm University (barbel.muller-karulis@su.se)

Authors:

Michelle McCrackin, Stockholm University  (michelle.mccrackin@su.se)

Benoit Dessirier, Stockholm University  (benoit.dessirier@su.se)

Bo Gustafsson, Stockholm University  (bo.gustafsson@su.se)

Christoph Humborg, Stockholm University  (christoph.humborg@su.se)