U. Dragosits

Integrating nitrogen fluxes at the European scale

Executive summary Nature of the problem • Environmental problems related to nitrogen concern all economic sectors and impact all media: atmosphere, pedosphere, hydrosphere and anthroposphere. • Therefore, the integration of fluxes allows an overall coverage of problems related to reactive nitrogen (Nr) in the environment, which is not accessible from sectoral approaches or by focusing on specific media. Approaches • This chapter presents a set of high resolution maps showing key elements of the N flux budget across Europe, including N2 and Nr fluxes. • Comparative nitrogen budgets are also presented for a range of European countries, highlighting the most efficient 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 different segments of Europe’s society. Key findings • From c. 18 Tg Nr yr −1 input to agriculture in the EU-27, only about 7 Tg Nr yr− 1 find their way to the consumer or are further processed by industry. • Some 3.7 Tg Nr 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 Nr 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 Nr yr−1. • The largest single sink for Nr appears to be denitrifi cation to N2 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 Nr 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 fill 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 different 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 effective tool to prioritize measures and prevent unwanted side effects.

Modelling the spatial distribution of ammonia emissions in the UK

Ammonia emissions (NH3) are characterised by a high spatial variability at a local scale. When modelling the spatial distribution of NH3 emissions, it is important to provide robust emission estimates, since the model output is used to assess potential environmental impacts, e.g. exceedance of critical loads. The aim of this study was to provide a new, updated spatial NH3 emission inventory for the UK for the year 2000, based on an improved modelling approach and the use of updated input datasets. The AENEID model distributes NH3 emissions from a range of agricultural activities, such as grazing and housing of livestock, storage and spreading of manures, and fertilizer application, at a 1-km grid resolution over the most suitable landcover types. The results of the emission calculation for the year 2000 are analysed and the methodology is compared with a previous spatial emission inventory for 1996.

Parallelisation and application of a multi-layer atmospheric transport model to quantify dispersion and deposition of ammonia over the British Isles

An atmospheric transport model, FRAME (Fine Resolution AMmonia Exchange), has been used to model the spatial pattern of ammonia concentrations and deposition over the British Isles for the first time. The model uses a multi-layer approach with diffusion through 33 layers to describe vertical concentration profiles in the atmosphere explicitly. Together with the necessary description of atmospheric reactions with sulphur and oxidised nitrogen, this imposes a major computational requirement, with the model having a run-time of 8.5 days on a mid-range workstation. Improvement in the model run-time was sought by developing a parallel implementation coded in a data-parallel approach using High Performance Fortran. Running the code on a Cray T3E with 128 processors provided a speedup by a factor of 69. The codes portability, its validation with measurements and new maps of its application to the British Isles, are presented. Good agreement is found with measured NH3 concentrations, while wet de-position is underestimated. In addition to model uncertainties, this may be due to an underestimation of the NH3 emissions input data.

Nitrogen flows and fate in rural landscapes

Nature of the problem Th e transfer of nitrogen by either farm management activities or natural processes (through the atmosphere and the hydrological net• work) can feed into the N cascade and lead to indirect and unexpected reactive nitrogen emissions. Th is transfer can lead to large N deposition rates and impacts to sensitive ecosystems. It can also promote further N • 2 O emission in areas where conditions are more favourable for denitrifi cation. In rural landscapes, the relevant scale is the scale where N is managed by farm activities and where environmental measures are • applied.

Sources, Dispersion and Fate of Atmospheric Ammonia

Publisher Summary This chapter reviews the current state of knowledge on the sources, dispersion and fate of atmospheric ammonia. Ammonia (NH 3 ) is a highly reactive and soluble alkaline gas, which occurs naturally in the atmosphere. It originates from both natural and anthropogenic sources, with the main source being livestock agriculture. Although the processes responsible are considered “ natural, ” the emissions generated from manures can be considered anthropogenic in nature, due to the influence of human management, both regarding the nitrogen input to livestock feed and the spatial concentration in so-called “ emission hot-spots ” due to high-density intensive farming practices. This chapter covers the characteristics, spatial distribution, and temporal trends of emission sources, dispersion, deposition and effects on the environment, at multiple scales from local to global. Modeling and measurement methodologies are discussed, including combinations of these approaches for validation. Finally, it addresses issues of emission abatement and policy strategies, taking account of links with other forms of nitrogen and pollution swapping.