National Nitrogen Budgets - A Systematic Approach to Combine and Evaluate Multiple Information on Environmentally Relevant Nitrogen Compounds

As environmental policies are largely structured according to individual problem areas, while nitrogen compounds involved in the "nitrogen cascade" affect all of them, potiential synergies of measures are often ignored or undervalued. Under the UN Economic Commission for Europe, this situation is about to be changed with guidance developed to create National Nitrogen Budgets (NNBs). NNBs systematically combine information on nitrogen flows in and between different environmental media, with different problems associated and from different physical sources while exploiting different information sources. Structured NNBs, in eight individual environmental "pools" and their sub-pools, use the principle of material conservation on the level of the total of nitrogen compounds - fixing nitrogen from the elemental form is considered a source, denitrification a sink of reactive nitrogen. Using stocks and flows on the respective pools, missing information on flows can be appended, and discrepancies identified where further improvements are needed to our understanding of the anthropogenic impacts on the nitrogen cycle. In agreement with the availability of statistical information, data are compiled on an annual basis by individual country - first of all aiming for application in countries with a robust statistical information system like the countries of the European Union, but targeting generally on the UN-ECE region (Europe, Caucasus and Central Asia). The systematic collection of the results of NNBs, their implementation in a database and their harmonization with other data collection activities performed by national authorities for the fulfillment of international environmental agreements have been further underlying elements in creating the guidance. Examples from pioneering studies implementing the guidance demonstrate, first of all, the potentials of benchmarking between different countries, different years or different source sectors. Owing to the discrepancies observed between independent datasets the need to further improve our understanding of the fate of reactive nitrogen compounds becomes evident.