• Nitrogen flows from European regional watersheds
Auteur:Billen, Gilles; silvestre, Marie; Grizzetti, Bruna; Leip, Adrian; Garnier, Josette; Voss, Maren; Howarth, Robert; Bouraoui, Fayçal; Lepistö, Ahti; Kortelainen, Pirkko; Johnes, Penny; Curtis, Chris; Humborg, Christoph; Smedberg, Erik; Kaste, Øyvind; Ganeshram, Raja; Beusen, Arthur; Lancelot, Christiane
Editeur scientifique:Sutton, Mark A.; Howard, Clare M.; Erisman, Jan Willem; Billen, Gilles; Grennfelt, Peringue; van Grinsven, Hans; Grizzetti, Bruna
Informations sur la publication:The European Nitrogen Assessment, Sources, Effects and Policy Perspectives, Cambridge University Press, Ed. 1, page (271-297)
Statut de publication:Publié, 2011-04-01
Sujet CREF:Environnement et pollution
Note générale:Nature of the problem • Most regional watersheds in Europe constitute managed human territories importing large amounts of new reactive nitrogen. • As a consequence, groundwater, surface freshwater and coastal seawater are undergoing severe nitrogen contamination and/or eutrophication problems. Approaches • A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fi xation, fertiliser use and import of food and feed has been carried out for all European watersheds. A database on N, P and Si fl uxes delivered at the basin outlets has been assembled. • A number of modelling approaches based on either statistical regression analysis or mechanistic description of the processes involved in nitrogen transfer and transformations have been developed for relating N inputs to watersheds to outputs into coastal marine ecosystems. Key fi ndings/state of knowledge • Th roughout Europe, NANI represents 3700 kgN/km2/yr (range, 0–8400 depending on the watershed), i.e. fi ve times the background rate of natural N 2 fi xation. • A mean of approximately 78% of NANI does not reach the basin outlet, but instead is stored (in soils, sediments or ground water) or eliminated to the atmosphere as reactive N forms or as N 2 . • N delivery to the European marine coastal zone totals 810 kgN/km2/yr (range, 200–4000 depending on the watershed), about four times the natural background. In areas of limited availability of silica, these inputs cause harmful algal blooms. Major uncertainties/challenges • Th e exact dimension of anthropogenic N inputs to watersheds is still imperfectly known and requires pursuing monitoring programmes and data integration at the international level. • Th e exact nature of ‘retention’ processes, which potentially represent a major management lever for reducing N contamination of water resources, is still poorly understood. • Coastal marine eutrophication depends to a large degree on local morphological and hydrographic conditions as well as on estuarine processes, which are also imperfectly known. Recommendations • Better control and management of the nitrogen cascade at the watershed scale is required to reduce N contamination of ground- and surface water, as well as coastal eutrophication. • In spite of the potential of these management measures, there is no choice at the European scale but to reduce the primary inputs of reactive nitrogen to watersheds, through changes in agriculture, human diet and other N fl ows related to human activity.
Chapter 13:
Note edition:1