Future trends in worldwide river nitrogen transport and related nitrous oxide emissions: a scenario analysis

We analyze possible future trends in dissolved inorganic nitrogen (DIN) export by world rivers and associated emissions of nitrous oxide (N2O). Our scenarios either assume that current trends continue or that nitrogen (N) inputs to aquatic systems are reduced as a result of changes in agriculture practices and fuel combustion technologies. The results indicate that moderate changes in the human diet in North America and Europe, reducing worldwide fertilizer use by only 16%, relative to Business-as-Usual (BAU) levels, may reduce DIN export rates to the North Atlantic and European Seas by about one third and associated N2O emissions by 36 to 77%. We furthermore calculate that relatively large reductions in NOy deposition rates in Europe (of about 80%) may reduce DIN export by rivers by a moderate 8% or less, relative to BAU levels. The potential effect of reduced NOy deposition on riverine DIN export is moderate, because most N in European rivers stems from agriculture, and not from fuel combustion. Nevertheless, the calculated 9% reduction (relative to BAU) in DIN inputs to the North Sea as a potential side effect of air pollution control may help achieve the international policy targets for reduced N inputs to the North Sea.