The role of atmospheric deposition in the eutrophication of the North Sea: A model analysis

This study quantifies the relative contribution of atmospheric deposition to total nitrogen in the southern North Sea in a spatial and temporal context. This is done by means of a biogeochemical model analysis using the Delft3D Generic Ecological Model (GEM). Tracer based model results show that atmospheric deposition accounts for 6% of the external nitrogen inputs in the North Sea. This percentage, however, varies strongly per region. For example, in the OSPAR area NLO2 (Oystergrounds and vicinity), 16% of the total nitrogen originates from atmospheric deposition.To test whether atmospheric deposition also affects other eutrophication related variables, comparative model experiments were carried out in which model-based net deposition fluxes of nitrogen are included and excluded, respectively. Model results show that primary production rates are disproportionately affected by atmospheric deposition, which is due to a change in the carbon-to-nitrogen ratio. Furthermore, evaluation of O2 time series at Oystergrounds indicate that in offshore areas that are prone to hypoxia, the atmospheric nitrogen flux may just be a critical contribution to oxygen depletion.

► Tracer based model results show that atmospheric deposition accounts for 6% of the external nitrogen inputs in the North Sea. ► Impact of atmospheric deposition strongly varies per region. ► Primary production rates are affected disproportionately by atmospheric deposition. ► In areas that are prone to hypoxia, the atmospheric nitrogen flux may just be a critical contribution to oxygen depletion.