Integrating Nitrogen Fluxes at the European Scale

Abstract

Environmental problems related to nitrogen concern all economic sectors and impact all media: atmosphere, pedosphere, hydrosphere and anthroposphere. Therefore, the integration of fl uxes allows an overall coverage of problems related to reactive nitrogen (N r ) in the environment, which is not accessible from sectoral approaches or by focusing on specifi c media. This chapter presents a set of high resolution maps showing key elements of the N fl ux budget across Europe, including N2 and Nr fluxes. Comparative nitrogen budgets are also presented for a range of European countries, highlighting the most effi cient strategies for mitigating Nr problems at a national scale. A new European Nitrogen Budget (EU-27) is presented on the basis of state-of-the-art Europe-wide models and databases focusing on diff erent segments of Europe’s society. From c . 18 Tg Nr yr−1 input to agriculture in the EU-27, only about 7 Tg N r yr− 1 fi nd their way to the consumer or are further processed by industry. Some 3.7 Tg N r yr −1 is released by the burning of fossil fuels in the EU-27, whereby the contribution of the industry and energy sectors is equal to that of the transport sector. More than 8 Tg N r yr −1 are disposed of to the hydrosphere, while the EU-27 is a net exporter of reactive nitrogen through atmospheric transport of c . 2.3 Tg N r yr−1. The largest single sink for Nr appears to be denitrifi cation to N 2 in European coastal shelf regions (potentially as large as the input of mineral fertilizer, about 11 Tg N yr –1 for the EU-27); however, this sink is also the most uncertain, because of the uncertainty of N r import from the open ocean. Major uncertainties: National nitrogen budgets are diffi cult to compile using a large range of data sources and are currently available only for a limited number of countries. Modelling approaches have been used to fi ll in the data gaps in some of these budgets, but it became obvious during this study that further research is needed in order to collect necessary data and make national nitrogen budgets inter-comparable across Europe. In some countries, due to inconsistent or contradictory information coming from diff erent data sources, closure of the nitrogen budget was not possible. Recommendations: • The large variety of problems associated with the excess of Nr in the European environment, including adverse impacts, requires an integrated nitrogen management approach that would allow for creation and closure of N budgets within European environments. • Development of nitrogen budgets nationwide, their assessment and management could become an eff ective tool to prioritize measures and prevent unwanted side effects.