Nutrient cycling and N₂O emissions in a changing climate: the subsurface water system role

This study has quantified the subsurface (groundwater, soil, sediment) water system role for hydrological nitrogen (N) and phosphorus (P) loading to the coast and agricultural N₂O emissions to the atmosphere in a changing climate. Results for different climate and hydrological model scenarios in the Swedish Norrström drainage basin show that the subsurface water system may largely control a long-term increase in the coastal nutrient loading, in particular for P, irrespectively of the realized future climate change scenario and our uncertainty about it and its water flow effects. The results also indicate an important subsurface water system role for current atmospheric N₂O emissions from agriculture, and an even greater role for future ones. The current N₂O–N emissions from agriculture are quantified to be about 0.05 g m⁻² yr⁻¹ over the basin surface area, or 3% of the direct N mass application on the agricultural land. These results are consistent with recent global emission estimates, and show how the latter can be reconciled with previous, considerably smaller subsystem emission estimates made by the IPCC (Intergovernmental Panel on Climate Change).