National nitrogen budget for Germany

Abstract

Emissions of reactive nitrogen (Nr) 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 Nr. 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 Nr 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 Nr a−1. Import of food, feed and materials contributes 745 kt Nr a−1, while biological N fixation converts 308 kt Nr a−1 into organically bound nitrogen. In terms of Nr sinks, the combustion and denoxing of fuels and the refining of crude oil converts 2,594 kt Nr a−1 to N2. In waters, soils, and wastewater treatment plants, denitrification leads to the release of 1,107 kt Nr a−1 as N2. Via the atmosphere and hydrosphere, Germany exports 755 kt Nr a−1 to neighbouring countries and into coastal waters. On balance, Germany releases 1,627 kt Nr 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.