Modeling global nutrient export from watersheds

We describe how global models can be used to analyze past and future trends in nutrient export from watersheds and how such models can be used to analyze causes and effects of coastal eutrophication. Future nutrient inputs to coastal waters may be higher than today, and nutrient ratios may depart from Redfield ratios, but not in all world regions. We discuss the strengths and weaknesses of available nutrient export models. We argue that future global nutrient export models are preferably dynamic, distributed and mechanistic. There is a need for agricultural and sanitation policies aimed at reducing coastal eutrophication. More measurements of nutrients in rivers are needed, especially in the tropics.