National nitrogen budget for Germany

Emissions of reactive nitrogen (N-r) give rise to a wide range of environmental problems. Nitrogen budgets for various systems and on different scales are an established tool to quantify the sources and fate of N-r. The national nitrogen budget (NNB) for Germany calculates the nitrogen flows for eight pools: Atmosphere, Energy and Fuels, Material and Products in Industry, Humans and Settlements, Agriculture, Forest and Semi-natural Vegetation, Waste, and Hydrosphere, as well as for the transboundary N-flows. In Germany, in total 6,275 kt N-r a(-1) has been introduced into the nitrogen cycle annually (mean 2010 to 2014), of which 43% stem from ammonia synthesis. Domestic extraction and import of nitrogenous fossil fuels (lignite, coal, crude oil) releases another 2,335 kt N-r a(-1). Import of food, feed and materials contributes 745 kt N-r a(-1), while biological N fixation converts 308 kt N-r a(-1) into organically bound nitrogen. In terms of N-r sinks, the combustion and denoxing of fuels and the refining of crude oil converts 2,594 kt N-r a(-1) to N-2. In waters, soils, and wastewater treatment plants, denitrification leads to the release of 1,107 kt N-r a(-1) as N-2. Via the atmosphere and hydrosphere, Germany exports 755 kt N-r a(-1) to neighbouring countries and into coastal waters. On balance, Germany releases 1,627 kt N-r a(-1) annually to the environment. However, the NNB as a whole and the individual pool balances involve substantial uncertainties, which have to be considered when interpreting the results.