Development of the global terrestrial nitrogen model WaterGAP-N

UNEP's Global Environmental Outlook 2000 recognized that nitrogen pollution has become a global problem that does no longer affect only developed countries. Due to the future increase of population and wealth, and the related extension and intensification of agriculture, many areas of the globe will potentially be subject to high nitrate levels in the groundwater and the eutrophication of surface waters (terrestrial and marine).

Nitrogen is an important component of plant, animal and human cells. Therefore, nitrogen fertilizers are often applied to increase crop production. The crop biomass is used as livestock fodder, and both vegetal and livestock products are used in human nutrition. Consequently, N is released to the environment from livestock and human excretions. Thus N is a component of the world’s biomass which can be transferred to soil, water and the atmosphere. N is the major component of the atmosphere, in the form of N2and a number of more reactive trace gases, some of which stem from the burning of fossil fuels or other human activities.

Many different pools of N in atmosphere, biosphere, hydrosphere or soils can be distinguished, and N is transferred by a variety of processes from one pool to another. The transfer often entails a change of the chemical structure. Because of this complexity, the description and quantification of pools, transport and transformation processes on a global scale is difficult and fraught with many uncertainties.

The purpose of the model WaterGAP-N is to get an overview of the present-day global situation of nitrogen input and fate (e.g. the transport of terrestrial N into the oceans), and to derive scenarios of the future that simulate the impact of global change (climate, population, agriculture, waste water treatment, etc.). WaterGAP-N simulates the input and fate of terrestrial nitrogen, including the input from diffuse (industrial fertilizer and manure, biological fixation, and atmospheric deposition) and point sources and the transport of dissolved N and its outgassing by denitrification in the soil and the groundwater as well as in surface waters (rivers, lakes, wetlands). With a spatial resolution of 0.5°, it computes the N loads in each cell as well as the input to the oceans. WaterGAP-N is based on information from the global model of water availability and water use WaterGAP 2.1 (Döll et al. 2003).

Specific research activities:

Keywords: nitrogen, nutrient cycle, eutrophication, water quality, fresh water, groundwater, surface water

Participants: Stefan Siebert,PetraDöll

Cooperating institutions: -

Duration: since 2003 (ongoing)

Funding entity: state funds

Contact: hydrology@em.uni-frankfurt.de