This fig. 4 show us the flow and quantity of Nitrogen in relation from an area of Saclay plateau. Area that is located in a green belt of Île-de-France region and at the crossroad of several administrative entities. The notion of Green Belt was formalized by the institute for development and planning for Île-de-France. The Green Belt is an area between 10 and 30 km from the gates of Paris where all the wooded, agricultural and natural spaces are preserved and developed.