Regional nitrogen budgets and riverine N & P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences

• Main Authors: Howarth, Robert, Billen, Gilles, Swaney, Dennis, Townsend, Andrea, Jaworski, N., Lajtha, Kate, Downing, John, Elmgren, Ragnar, Caraco, Nina, Jordan, Teresa, Berendse, F., Freney, Jean, Kudeyarov, V., Murdoch, Peter, Zhu, Zhao-Liang
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1996
• Subjects: Géologie et minéralogie; Technologie de l'environnement; contrôle de la pollution; Traitement des eaux résiduaires; Traitement de potabilisation de l'eau; Anthropogenic; Atmospheric deposition; Eutrophication; Fertilizer; N:P ratio; Nitrogen; Nitrogen budget; Nitrogen fixation; Phosphorus; Pristine; Rivers; Temperate; Tropical; North Atlantic
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/165884; https://dipot.ulb.ac.be/dspace/bitstream/2013/165884/4/a331bbca-f806-45f0-aee0-b8ee84bcc9c1.txt

We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also large, contributing 3.3 Tg yr -1 out of a total for the entire North Atlantic region of 13.1 Tg yr -1. On a per area basis, however, the largest nitrogen fluxes are found in the highly disturbed watersheds around the North Sea, in northwestern Europe, and in the northeastern U.S. all of which have riverine nitrogen fluxes greater than 1,000 kg N km -2 yr -1. Non-point sources of nitrogen dominate riverine fluxes to the coast in all regions. River fluxes of total nitrogen from the temperate regions of the North Atlantic basin are correlated with population density, as has been observed previously for fluxes of nitrate in the world's major rivers. However, more striking is a strong linear correlation between river fluxes of total nitrogen and the sum of anthropogenically-derived nitrogen inputs to the temperate regions (fertilizer application, human-induced increases in atmospheric deposition of oxidized forms of nitrogen, fixation by leguminous crops, and the import/export of nitrogen in agricultural products). On average, regional nitrogen fluxes in rivers are only 25% of these anthropogenically derived nitrogen inputs. Denitrification in wetlands and aquatic ecosystems is probably the dominant sink, with storage in forests perhaps also of importance. Storage of nitrogen to groundwater, although of importance in some localities, is a very small sink for nitrogen input in all regions. Agricultural sources of nitrogen dominate inputs in many region, particularly the Mississippi basin and the North Sea drainages. Deposition of oxidized nitrogen, primarily of industrial origin, is the major control over fiver nitrogen export in ...