Global-scale scenarios and modelling as tools for managing large-scale nitrogen pollution
UNEP's GEO Yearbook 2003 (UNEP, 2004) characterizes problems related to reactive nitrogen (nitrogen overloads in some areas and nitrogen deficiencies in other areas of the globe) as an emerging global environmental issue. Global modelling and scenario analysis may help to investigate linkages and feedbacks between global change and water pollution, and to identify appropriate management options. To get an overview of the present-day global situation of nitrogen input and fate and to derive scenarios of the future that simulate the impact of global change (climate, population, agriculture, waste water treatment, etc.), the global model WaterGAP-N is being developed. WaterGAP-N will simulate 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 loss by denitrification in soil and groundwater as well as in surface waters (rivers, lakes, wetlands). With a spatial resolution of 0.5°, the model computes the N loads in each cell as well as the input to the oceans. Here we present first results of WaterGAP-N and show how the model will be used to derive management options for large-scale nitrogen pollution on the background of the SRES scenarios of the Intergovernmental Panel on Climate Change (IPCC).