The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean

• Main Authors: Nixon, Scott S.W., Berounsky, Veronica V.M., Pilson, Michael E Q, Ammerman, James J.W., Atkinson, Larry, Billen, Gilles, Boicourt, William W.C., Boynton, Walter W.R., Church, Thomas T.M., Ditoro, Dominic D.M., Elmgren, Ragnar, Garber, Jonathan J.H., Giblin, Anne A.E., Jahnke, Richard R.A., Owens, Nicholas J P, Seitzinger, Sybil
• 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; continential shelf; estuaries; mass balance; nitrogen; North Atlantic; nutrient budget; phosphorus
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/183988; https://dipot.ulb.ac.be/dspace/bitstream/2013/183988/4/c3a38fe0-baa8-4974-8d49-325364870d9c.txt

Five large rivers that discharge on the western North Atlantic continental shelf carry about 45% of the nitrogen (N) and 70% of the phosphorus (P) that others estimate to be the total flux of these elements from the entire North Atlantic watershed, including North, Central and South America, Europe, and Northwest Africa. We estimate that 61 · 10 9 moles y - 1 of N and 20 · 10 9 moles y -1 of P from the large rivers are buried with sediments in their deltas, and that an equal amount of N and P from the large rivers is lost to the shelf through burial of river sediments that are deposited directly on the continental slope. The effective transport of active N and P from land to the shelf through the very large rivers is thus reduced to 292 · 10 9 moles y -1 of N and 13 · 10 9 moles y -1 of P. The remaining riverine fluxes from land must pass through estuaries. An analysis of annual total N and total P budgets for various estuaries around the North Atlantic revealed that the net fractional transport of these nutrients through estuaries to the continental shelf is inversely correlated with the log mean residence time of water in the system. This is consistent with numerous observations of nutrient retention and loss in temperate lakes. Denitrification is the major process responsible for removing N in most estuaries, and the fraction of total N input that is denitrified appears to be directly proportional to the log mean water residence time. In general, we estimate that estuarine processes retain and remove 30-65% of the total N and 10-55% of the total P that would otherwise pass into the coastal ocean. The resulting transport through estuaries to the shelf amounts to 172-335 · 10 9 moles y -1 of N and 11-19 · 10 9 moles y -1 of P. These values are similar to the effective contribution from the large rivers that discharge directly on the shelf. For the North Atlantic shelf as a whole, N fluxes from major rivers and estuaries exceed atmospheric deposition by a factor of 3.5-4.7, but this varies widely among regions ...