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|Title:||Nitrogen Flows from European Regional Watersheds to Coastal Marine Waters|
|Authors:||BILLEN Gilles; SILVESTRE Marie; GRIZZETTI Bruna; LEIP Adrian; GARNIER Josette; VOSS M.; HOWARTH ROBERT W.; BOURAOUI Faycal; LEPISTÖ L.; KORTELAINEN Pirkko; JOHNES Penny; CURTIS Chris; HUMBORG Christoph; SMEDBERG Erik; KASTE Øyvind; GANESHRAM R. S.; BEUSEN Arthur; LANCELOT Christiane|
|Publisher:||Cambridge University Press|
|Type:||Articles in periodicals and books|
|Abstract:||Most regional watersheds in Europe constitute deeply 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. A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fixation, fertilizer use and import of food and feed has been carried out. A data base on N, P and Si fluxes delivered at the basin outlets has been assembled. A number of modelling approaches, either based on statistical regression analysis or on 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. Over Europe, NANI represents 3700 kgN/km²/yr (range 0- 8400), i.e. 5 times the background rate of natural N2 fixation. About 78% of NANI is stored or eliminated to the atmosphere before reaching the basin outlet. N delivery to the coastal zone amounts 810 kgN/km²/yr (ranging from 200-4000 according to watersheds), representing about four times the natural background. Large imbalance with respect to silica causes harmful algal blooms. The exact nature of "retention" processes, which potentially represent a major management leverage for reducing N contamination of water resources, is still poorly understood. Coastal marine eutrophication strongly depends on local morphological and hydrographical conditions, as well on estuarine processes, which are also imperfectly known. A 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.|
|JRC Directorate:||Sustainable Resources|
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